Category Archives: Emergency Room

Somebody call the Doctor! “Emergency Room” posts document repairs done on the Mimmotronics repair bench. We’ll start at the root of the problem, weave our way through the jungles of the troubleshooting process, and arrive at the other side with our guitars singing straight through the resurrected pedal. Think of Sherlock Holmes…only applied to guitar pedal repair!

Emergency Room #12: The Silent ZenDrive

Espoused by guitarists like Robben Ford, Sonny Landreth, and Nalle Colt, the ZenDrive by Hermida Audio continues to live up to overdrive connoisseurs. This particular overdrive is an NE5532 Op Amp based drive, and the one ending up on the bench today suffered from an op amp gone awry.

ZenDrive Gut Shot featuring the NE5532 op amp, the heart of the ZenDrive circuit.

ZenDrive Gut Shot featuring the NE5532 op amp, the heart of the ZenDrive circuit.

The original complaint was that no output could be heard when engaging the effect, but when bypassed all was well. On opening the backplate and removing the circuit board I was surprised that the op amp used in this unit was seated in an IC socket. This made the repair much easier (thanks Hermida Audio!). I removed the op amp, breadboarded it within a simple buffer circuit and, sure enough, the op amp’s I/O terminals were stuck at the rails. Replacement with another NE5532 fixed the issue.


This fix was done for Buffalo-based guitarist Matt Fantini of Space Junk. Check them out at Funk n’ Waffles Rochester on January 10th with special guests SKYwalker!

Emergency Room #11: Furman HDS-6 Headphone Distribution System

This round of Emergency Room features the 6-channel Furman HDS-6 Headphone Distribution System after a mild power surge incapacitated 5 of the 6 channels. This unit is pretty neat, it utilizes Cat 5 cabling to distribute power and channel signals to remote units (HR-6’s) which are used in the studio booth by the recording artist for monitoring the other tracks through a pair of headphones. The HR-6 can be daisy-chained with other HR-6 units, enabling recording artists the ability to locally monitor tracks while recording.

Figure 1: Showing the HR-6 Headphone Remote unit connected to the HDS-6 main board for a test-run.

I opened up the chassis and, after some visual inspection, saw one of the capacitors had blown. I replaced the cap and powered the unit back up; no good. Other than that there was an odd white discoloration of the main board around one other capacitor. It didn’t seem to be an issue, but I replaced the cap it was surrounding for good measure. There was no schematic to go by, so I traced out one of the channels and drafted it for reference (shown below). I have a more detailed schematic written out, if needed don’t hesitate on sending me a message.

Figure 2: Mock-schematic detailing the HDS-6s signal path.

This revealed two op amps utilized in the signal path. This unit has six identical channels, so the circuit above is duplicated 5 times with only the component names varying, making it easy to troubleshoot the rest of the unit.

I injected an audio signal into each of the channels and probed the signal paths. This revealed that, for almost every channel, the second op amp in the signal path wasn’t functioning. This was confirmed when measuring the DC voltages on each op amp chip. The figure below shows the voltage measurements for the three dual op amp chips U101, U201 and U301:

Figure 3: Showing all three defective op amp values. These should all be biased to 0V!

I had a couple TL082s on-hand, and replacing them fixed the issue. The TL082 has an input noise voltage of 16nV/√Hz, but if available, replacement with something with a lower input noise voltage like an NE5532 is recommended since these particular op amps are in the signal path.

Figure 4: One of the newly installed op amp ICs.

Thanks for visiting! If you have a piece of gear needing repair contact me here and please follow Mimmotronics on Instagram and Facebook. This fix was done for DMS Productions located in Ransomville, NY!

Emergency Room #10: Juno-106 Acetone Treatment

“The essence of the beautiful is unity in variety.”

– Felix Mendelssohn –

Where there is art, there is beauty. And according to Felix, where there is beauty, there is variety. The audio electronics world is no exception. There are multitudes of audio effects out on the market, and the common differences they exhibit renders their design an art form all its own. This blog generally deals with audio effects equipment, but the diverse nature of the audio world prevents me from dealing solely with guitar effects repairs. Today we turn our attention to a popular synthesizer from 1984, the Roland Juno-106 Analog Polyphonic Synthesizer.

This thing is a BEAST! But these days, there’s a common problem that owners of these synths should look out for: the failure of the Roland AR80017 Voice Chips. Apparently this is a super common problem with these units, and if you’re here reading this you’re probably suspecting the voice chips to be the reason for your faulty Juno.

In order to isolate the problem to the voice chips you’ll have to utilize the Juno’s built-in troubleshooting method described in EXPLORING AUDIO’s YouTube video, “ROLAND JUNO 106 : VOICE CHIP ISSUES.” You can also find the procedure on page 18 in the Juno’s service manual, found here.

 

Once the problem is isolated to the Juno’s voice chips the procedure described by Jeroen Allaert of Analogue Rensaissance can be used to remove them. Allaert has done some remarkable work on the AR80017A voice chip; he’s even re-engineered a replica of it which can be purchased from his website. Another replica chip can be bought through ModularAddict.com as well. So even if the following procedure doesn’t do the trick, there are replacements available.

Once the chips are removed you can start the dissolving process! Fill a glass container with acetone (100% is best) and submerge the chips. Let that sit for 24-48 hours and check the condition of the outer epoxy resin cover. You can tell when the acetone has done its job by how disassociated the resin becomes. Gently peel off the larger chunks of resin and use a small tool (something similar to a precision flat-head screwdriver) for removing the smaller bits of resin left behind.

The reason acetone is used is because its a solvent for plastics (rubbers, polyethylene, etc.). It does a great job at breaking down polymers, and the epoxy resin encasing the voice chip is a decent candidate for the dissolving reaction. In fact, excess glue can also be removed using this method.

Once most of the resin is removed you can solder them back into the board. A good pair of helping hands or something to prop the board on its side is essential in order to easily solder the chips back into place. Solder one pin to support the chip on the board, then solder the rest of the pins with relative ease.

That’s it! Thanks for visiting Mimmotronics, please follow the Instagram and Facebook pages if you liked the post. Stay tuned!


This post was done as a result of working with Cody Morse, guitarist for Buffalo, NY, psych-rock band Deadwolf. on his faulty Juno-106 synthesizer. See their feature in the Buffalo internet TV show, the Attic:

Emergency Room #9: Delta Labs Super Timeline ADM2048 Battery Burst

This is quite possibly the most interesting circuit I’ve worked on so far. I’ve always wondered how a digital delay works, and this late ’80s digital IC-based technology allowed the opportunity to reverse engineer the general concept. (I’ll share those findings in posts to come!) But before I could reverse engineer anything the unit had to be repaired to a working condition, as it had suffered the results of a failed board-mounted 4.6V battery:

Figure 1: Showing the Damage from Battery Leakage

There is an SRAM chip (NMC6504) used on this board to store 4 preset configurations (A, B, C & D), this is obviously being powered by the battery and was confirmed when I replaced the blown fuse, powered up the device, and no presets were able to be saved.

I couldn’t find the specs for this battery model online for a direct replacement, so I had to dig into many forums to find information and, eventually, a schematic. For legal reasons I won’t post the schematic here, contact me for more info if needed.

The schematics yield a 4.6V battery, and the test point for the battery voltage is labeled +5VB after the zener. I settled on a Varta 4.8V NiMH from JLS Batteries on eBay. It’s a through-hole component, but doesn’t match the footprint of the original battery, so I soldered wires from the + and – sides to the appropriate vias. To secure the wiring to the battery’s body I used electrical tape and twisted the wires together to provide additional support. The electrical tape may also help in preventing a large amount of damage to occur in the case that this NiMH fails in the future. A square piece of Velcro was used to secure the battery to the main board.

The use of a NiMH is based on the color of the corrosion that occurred on the copper traces and component leads. NiMH batteries contain the hydroxide anion (OH-). In the presence of an electrical current and physical contact, the hydroxide anion and copper can react to form copper (II) hydroxide, which is blue in color.

Copper (II) Hydroxide suspended in a Test-Tube

Copper (II) Hydroxide suspended in a Test-Tube (WikiMedia Commons)

To reiterate, this reaction is corrosive and literally eats away the copper traces on the board. If enough corrosion takes place the board may become irreparable! (Or at least extremely hard to repair without re-engineering and rebuilding the affected circuit). Luckily, this was not the case for this unit.

Once the replacement battery was installed I powered up the Super Timeline and presets were operational!  The contacts for the presets, however, were extremely unreliable. They would make contact maybe 60% of the time, so I ended up removing all of the preset button switching actuators. I tinned a thin, even layer of solder onto each contact and reinstalled them; that worked very well.

Figure 2: Programmable preset switches. The switch to far left has its' actuator removed. This is done by applying a precision flat-head screwdriver to the plastic lip between the lug sets.

Figure 2: Programmable preset switches. The switch to far left has its’ actuator removed. This is done by applying a precision flat-head screwdriver to the plastic lip between the lug sets.

After tinning the preset contacts I took aim to the copper (II) hydroxide build-up near the power and LFO circuits. I cleaned a toothbrush with distilled water and started brushing the corrosion build-up off the leads. I quickly noticed that the component labeling was getting scraped off as if they were old stickers. From that point on I was very careful in removing the corrosive material and mainly focused on relatively open areas between components. It’s not perfectly cleaned, but the unit was working and I didn’t want to ruin the labeling scheme, as it may prove useful down the road. (If anybody has an abrasive-free solution for cleaning copper (II) hydroxide from PCBs I’d be highly interested!) To remove the distilled water I used some combination of paper towels, a hair dryer, and an air compressor.


Thanks for reading! Notes on the circuit’s operation will definitely be a topic for future Talk Theory To Me posts. Stay tuned if you’re interested!

This fix was done for DMS Productions located in Ransomville, NY!

“With over 22 years experience in audio, 16 years experience in photography and over 5 years in video, DMS Productions has become a true multimedia company.”

Decimator Title Pic

Emergency Room #8: The Discharging Decimator

Introducing: the iSP Decimator Noise Reduction unit! This is quite probably the best noise reducer I’ve played through thus far. There’s only one problem..it pops! You had one job Decimator!

Deal with it.

In any case, it’s a good thing the Decimator is in our hands. What’s happening is the pedal works correctly when set to -30dB and below. Problems are only seen when disengaging the pedal with the potentiometer past the 12:00 position. Engaging the pedal is fine but once we decide to disengage, it lets out a noticeable “pop” in the output. Turning the potentiometer clockwise from 12:00 makes the popping sound even more noticeable.

So we see two things here: (1) The popping intensity is dependent on the position of the potentiometer and (2) the popping only occurs when disengaging the pedal. Keep these in mind as we continue.

Okay, so now we have some clues. As an aside, when pedal-popping complaints arise it is usually a result of a DC current snaking its way into the signal path and eventually into the pedal’s output signal. Now I will admit to not knowing all the ways this can happen, but the primary cause is a build up of charge. This charge build-up only results in pedal pop when it quickly affects the output signal. The quicker the discharge, the “shriller” the pop. The slower the discharge, the “duller” the pop.

The same can be said on how filtered the pop is. If a pop is filtered enough it can be transformed into a “thud”-like sound. You can read more about that here.

After some careful thought the next thing to do is take a look at the schematic and try to pin-point possible areas where charge build-up can occur. But first…we need a schematic. I was pointed to Fred Brigg’s La Revolution Deux blog and found a schematic for an iSP Decimator model similar to what I had. Along with the schematic it’s nice to have the datasheets handy for any ICs or transistors onboard. This Decimator only uses 3 types of ICs:

  1. THAT2181C – Voltage Controlled Amplifier
  2. LF353 – Dual JFET Op Amps
  3. HEF4013 – Dual D-Type Flip-Flop

And 3 transistors:

  1. 2N5484 N-Channel JFET
  2. KSP222A NPN Gen. Purpose Amplifier
  3. 2N5551 NPN Amplifiers

Reading through some of the datasheets I suspect the THAT chip is intercepting a DC input voltage. Though, this is ruled out since there happens to be an input coupling capacitor which should thwart any chance of a DC voltage popping up at the input of the VCA.

Eventually I take another look at the schematic and realize the switching circuitry for the model I have isn’t conveyed. This is in fact directly related to the original problem, so maybe the solution lies in that area of the board…

I pull flex my reverse engineering muscle and trace out the Decimator’s switching circuit. This is important since it reveals a 2N5484 JFET transistor used to switch the pedal on and off. It’s important to understand conceptually how this switching circuit interacts with the rest of the circuit. I’ll explain the inner workings of how the pedal switches ON and OFF. (I’ve made a mock-schematic for you in Figure 1).

Figure 1 - Mock Schematic for Conceptual Use

Figure 1 – Mock Schematic for Conceptual Use, Final Mod is in Red (discussed later)

When the pedal is disengaged, the gate terminal of the JFET is too low of a voltage to allow current to pass through the source and drain terminals. This effectively severs the dependency of the input signal from the VCA’s operation, leaving only a virtual ground (4.5V set by an on-board potentiometer) applied to the Ec+ control pin (pin 2) of the VCA. This DC voltage is constant and, at 4.5V, the pedal sees virtual ground. (This is because the ground, pin 6, of the VCA chip is also seeing 4.5V, so in the chip’s perspective it’s ground.)

If we take a look at Figure 2 we see that when the chip sees a control voltage of 0V (in relation to it’s ground pin) the VCA gain is set to 0dB. This means the chip doesn’t amplify or attenuate. Whatever signal you put into it should also be received at the output.

Now let’s understand what’s going on when the pedal is engaged. Take yet another look at Figure 2. If we decrease our control voltage the amount of gain we apply to the input signal proportionally decreases. Essentially, when engaged, the circuit varies the DC voltage at this Ec+ control pin and this controls the amount of gain the VCA applies to the input signal.

Figure 2 – Note that the control voltage is in relation to virtual ground, so in this case our virtual ground and the control voltage are equal at 4.5V.

The control voltage is a function of two things: (1) the amplitude envelope of the input signal and (2) a user-controlled threshold voltage set by the potentiometer. If the input signal’s amplitude envelope is below the threshold voltage the circuit decreases the control voltage accordingly and the VCA attenuates the signal. If the input signal’s amplitude envelope is above the threshold voltage the circuit increases the control voltage such that the VCA eases off with the attenuation.

So how does the circuit increase or decrease the control voltage? By way of current! Firstly, both the input signal amplitude envelope and the threshold voltage are sent to a differential amplifier (which we can think of as a comparator for ease of discussion). This component increases or decreases it’s output voltage based on the comparison of its two input signals. This voltage is seen at the cathode side of a diode. The anode side sees the drain terminal of the 2N5484 FET. If the voltage across the diode (which is based on the comparison above) is positive enough, current starts to sink through the FET and resistor R37. This current produces a voltage difference across R37 that pulls the control voltage lower than virtual ground. This in turn provides the attenuation and, hence, “noise” reduction based on the plot in Figure 2.

Pretty cool, huh?

Now for the main take-away: This control voltage is only there because the FET is allowing current to pass through it. When the pedal goes from being engaged to being disengaged (i.e. when the gate voltage of the FET is suddenly hit with 9V from the switching circuit) the current providing the drop in control voltage ceases and the control voltage increases (or decreases) back to it’s original virtual ground of 4.5V.

This self-correction of control voltage is sudden. So sudden that this popping sound could be originated by it’s occurrence. If a fast voltage transition is the suspect, why not find a way to slow down this voltage transition?

Take your thinking cap out: what causes the voltage transition? In this case, it’s the step change generated by the switching circuit applied to the FET gate terminal. This type of step-change signal is depicted in Figure 3. All we need to do is smooth out this transition (Figure 4) while making it last long enough to not hear a “pop” in the output. We can achieve this by constructing an RC circuit at the gate terminal while choosing component values that allow a slower voltage transition.

Square wave/periodic step-changing signal

Figure 3 – Square wave (periodic step-changing signal)

Figure 4 - Same signal as Figure 3 showing the affects of applying an RC circuit

Figure 4 – Same signal as Figure 3 showing the effect of applying an RC circuit

The circuit already utilizes a 1M-ohm resistor at the gate terminal. What needs to be added is a capacitor between the gate terminal and ground (0V). I tested the pedal’s operation with a 103 ceramic capacitor branched between the gate terminal and ground. This allowed a softer fade out of the current through the FET which ultimately eliminated the “pop.” Awesome!

All that for adding a little capacitor! We got a bit technical this time around but nonetheless I hope you enjoyed this post! This one’s for Deadwolf guitarist and Afterglow Studios’ owner/producer Cody Morse. Look out for Deadwolf at Buffalo, NY’s HerdFest, June 17th at Dreamland!

Buffalo Herd Fest logo

EHX Small Stone Nano

Emergency Room #7: The Intermittent Small Stone

Another Small Stone on the bench! This time, the Nano. The problem? The LED would turn on but sometimes, when engaging the effect, the signal would entirely drop out. Other times it worked great. The first thing I like to do when an intermittent issue like this comes up is look for any mechanical devices that are directly involved in regenerating the problem. In this case, the 3PDT switch was the first thing to inspect.

Sure enough, the switch was the issue! But to be sure enough, I regenerated the problem. The signal was dropped out yet the LED indicator was on. Applying pressure to the shaft of the footswitch resulted in reviving the signal. On intuition, there is probably a loose connection internal to the switch that was shaken up from excessive use.

The Small Stone Nano sporting a new 3PDT switch

The Small Stone Nano sporting a new 3PDT switch

In the end, I replaced the 3PDT switch and the pedal was phasing once again! This is one area where it’s great getting to know the people you’re fixing things for. The Small Stone is heavily used in the band, which is important information for deducing the problem to an overused mechanical device.

This fix was done for Cody Morse of Afterglow Studios & Buffalo band, Deadwolf! Watch out for them, they’re coming up strong!

Emergency Room #6: The Touchy Fender Blender

The Fender Blender is one of those pedals that make pedal repair bittersweet. It’s such a unique fuzz! This classic is definitely one to consider cloning in the near future..possibly installed in a Furby enclosure…

But today, we’re focusing on a minor addition to the Fender Blender: installing indicator LEDs for the bypass and tone boost controls. Not only that but there is a sort of pressure point next to the bypass switch that, when pressed considerably changes the tone.

Let’s address this pressure point first. The pedal is held together by three screws. Upon opening and inspecting it I noticed two things right away. The first was a slightly loose white wire connected to the Tone Boost switch. This wasn’t the source of the pressure point problem but would be an issue at some point in the future, so I soldered that back in. The second was a lead from capacitor C15 which extended long enough to make contact with the chassis.

Showing the lead of C15 in contact with the inside of the chassis.

Notice the lead of C15 in contact with the inside of the chassis.

After this lead was cut the pressure point was relieved. No more unintended changes in tone! Next step is to install the two LEDs for bypass and tone boost controls. The installation required the swapping of the Fender Blender’s stock switches with two 3PDT footswitches. The connections remained the same with the exception of adding a line for the LEDs.

Fender Blender guts

Fender Blender guts

The positive leads for both LEDs were connected to 9V found at the forward-bias end of D5 and/or D6 diodes (in the bottom-left of the guts pic above). The ground connection was routed to the terminating end of the black wire from the bypass switch (again towards the left side of the picture above. The picture below depicts how I planned out the 3PDT wiring.

3PDT Wiring Mock-Up. Original wiring is shown on top, the new wiring is shown at the bottom.

3PDT Wiring Mock-Up. Original wiring is shown on top, the new wiring is shown at the bottom.

That’s it! One criticism I have with this pedals construction is the way their potentiometers are wired to the main board:

Showing the Potentiometer Connections to Main Board

Showing the Potentiometer Connections to Main Board

They soldered bare wires from the pot lugs directly onto the board. It seems to work but its not the most robust solution. If the pots were ever loose the joint force of rotating the pot to its limits might break the solder connection at the main board junction. A better solution, in my opinion, would be to use insulated wires along with non-insulated butt connectors for connecting to the main board.

This improvement & fix was done for Buffalo indie rock band Feverbox! Seek them out in and around digital platforms for their new EP being released April 28th, 2017.

Feverbox Logo

The EHX POG2

Emergency Room #5: EHX POG2 Slide-Pot Replacements

This last week I received an EHX POG2 for slide-pot (fader) replacements and their condition gave justice to the term “stompbox!” First step: some housekeeping work.

Remember to routinely shave your POG

NOTE: Remember to routinely shave your POG

All in all, it’s a fairly simple fix. The real hassle was removing the fader units, as they were located directly opposite to the Analog Devices DSP chip. Heat isn’t generally a good thing around those types of components. It’s recommended to make yourself some coffee/tea and take your time removing each solder pad so the heat doesn’t build up as quickly. To remove the solder I used a simple handheld spring-loaded desoldering pump and a soldering iron to heat the pad.

Note: using the desoldering gun alone might not be enough to remove all the solder…something to do with how efficiently the heat dissipates within the solder pad? If you see any solder leftover I suggest resoldering the pad with new solder and desoldering it again. Another method I found helpful, if possible, was to heat the pad from the front side of the board and activate the desoldering gun on the underside.

The construction of the slide-pots make them relatively simple to remove. There is a metal cover with 4 lugs, two on each side, that are soldered into the board (marked in RED). The linear potentiometer portion is positioned underneath the cover with three leads, two on the top side and one on the bottom (marked in YELLOW).

RED: The mounting lugs. YELLOW: The linear pot connections.

RED: The mounting lugs. YELLOW: The linear pot connections.

To remove the slide-pot I first desoldered both the cover and pot lugs. Next I took a pair of needle-nose pliers and lifted the top and bottom sides of the slide-pot cover. One by one I had to heat and pull out each lug until the whole cover was pulled off. After the cover was off the linear pot portion was easy to remove with a similar process.

As for the shaft-less rotary encoder, the device has 7 leads soldered onto the board, two of which are there purely for support. I desoldered all the associated pads and, to make things easier, I clipped each lead before fully removing the device. The leftover pins from clipping the leads are easily removed with a soldering iron, a pair of pliers, and some helping hands. It was then swapped with an exact replacement.

It’s impossible to know the values for the slide-pots unless you remove them. In this case all three were 5kohm.

5Kohms: Confirmed!

5Kohms: Confirmed!

Once the parts came in installation was no problem. The POG2 was well behaved during the entire process and is now fully operational.

This fix was done for Buffalo indie rock band Feverbox. Check out their new Feverbox EP coming out April 28th, 2017, on digital platforms and catch their next show with Mona among others at The Waiting Room in Buffalo, NY!

Emergency Room #4: EHX Small Stone Indicator LED

Waves – the only word I need to describe the Electro-Harmonix Small Stone Phase Shifter. It’s a great addition to your board, with only one caveat…there’s no indicator LED. In this day and age it’s almost a requirement to include this LED; but back in the early days of pedal-manufacturing when guitarists used up to just a handful of pedals (if that!), it wasn’t a necessity.

In this post I’m going to describe how I installed the indicator along with any problems that occurred along the way. Time to bring this old Small Stone into the 21st century!

Fun Fact: EH1048 OTA chips can also be replaced by CA3094s

The Small Stone I’m working on here is version 2 in it’s line. The circuit board design is marked “Issue J” and the schematic for it is provided below from next.ga. Something cool about this circuit: it sports a device (the EH1048) called an Operational Transconductance Amplifier (OTA). For those familiar with operational amplifiers (op amps), they are almost the same, except there are 2 additional current-based I/Os to take into account. I’m interested in a “Talk Theory To Me” post on this in the future, so I’ll leave that topic here.

EHX Small Stone Version 2 Issue J Board Schematic

EHX Small Stone Version 2 Issue J Board Schematic

In order to install an indicator LED we’ll need to switch it on or off depending on whether or not the effect is on or off, respectively. We can do this by hard-wiring a short LED circuit through the footswitch lugs. Sounds simple..problem is, the type of switch used in the Small Stone doesn’t allow for this addition. Look below for the wiring description of the stock SPDT footswitch. The output signal is connected to the common, one side is connected to the input signal (for by-pass) and the other to the output of the circuit board (for the effect).

Original SPDT Switch Wiring

Original SPDT Switch Wiring

To make this work I had to swap out the SPDT with at least a double-pole. The switches I had readily available were all 3PDT footswitches, so I used that. You can see how I wired it below, which worked just fine. There are other ways to wire a 3PDT switch and the way I chose works well. In the future, I’m considering a post showing each method’s pros and cons.

New 3PDT Switch Wiring

New 3PDT Switch Wiring

To make sure I correctly wired the 3PDT switch to the board I had to trace out which solder pads each of the wires had been connected to. With the help of the schematic – and with Microsoft Paint in my back pocket – I could give myself a reference to go by while wiring the new switch, shared below.

Small Stone Board Wiring Reference

Small Stone Board Wiring Reference: A – Up-Position #1 for Color Switch, B – Common #1 of Color Switch, C – Up-Position #2 for Color Switch, D – Common #2 for Color Switch, E – Down-Position #2 for Color Switch, F – 9VDC Power

The circuit board itself is only supported by the shaft of the potentiometer being used to alter the phase rate. This forced the board to be mounted in close proximity to the cover. A small, rectangular piece of foam supported the bottom portion of the board at the edge furthest away from the potentiometer mount for further support. This support system provided a small problem since the 3PDT switch was taller than the stock switch. Because of this the bottom lugs of the switch could easily touch the circuit board.

To get around this I cut the rectangular foam piece holding up the loose end of the circuit board about 3/4 down which provided enough leeway to (carefully!!) bend the potentiometer leads so as to angle the circuit board downwards from the knob. This provided enough space to mount the 3PDT switch. As an added measure, I electrically isolated the lugs of the 3PDT switch using one-sided tape and soldered all wires from the lugs such that none of them could push downwards and puncture the tape.

As for the LED, I had recently stocked up on some LED holders and LEDs from a local Radioshack, so I used them. The requested spot to drill was smack in the middle of the ‘O’ in “stone.” After taking the pedal off of the drill press I mounted the LED, soldered and heat-shrunk the leads, and tested out the finished installation. Works like a charm!

Thanks to Deadwolf guitarist and Afterglow Studios’ Cody Morse for the job! Deadwolf is Buffalo’s very own psychedelic rock band, check them out now!

 

Find Deadwolf on Twitter, Soundcloud, and Facebook along with other music-sharing sites.

Revived and Operational TC Electronics Finalizer

Emergency Room #3: T.C. Electronic Finalizer 96K Studio Mastering Processor

Recently I got my hands on a dead T.C. Finalizer Studio Mastering Processor from DMS Productions in Ransomville, NY. Right off the bat this sounds like a power supply problem.

The top panel is held down by 5 screws. Upon opening and inspecting the unit there are two main boards – the power supply unit and the main processing board. Focusing on the power supply, it is a switch-mode (SMPS) with a daughter-board vertically mounted next to the power transformer. SMPSs are inherently controlled via a pulse-width modulation (PWM) switching controller. For this unit, the PWM controller chip is mounted on the daughter-board – they use the Texas Instruments TL3842BP current mode PWM switching controller. The output of the PWM controller is fed into a TL431 Programmable Voltage Reference, which looks like a transistor at first glance. The voltage reference then is routed to other areas of the power supply to convert it to other DC voltages and clean it through some passive filtering.

PWM Controller Board Inside the Main Power Supply Unit

PWM Controller Board Inside the Main Power Supply Unit

Visual inspection reveals some corrosion on a capacitor and resistor sitting next to the daughter-board. There were also some other caps near the output power sources which had the same amount of corrosion.

Before electrical troubleshooting I thought it may be best to first search the forums on issues with this unit…boy were there issues! I’m notably grateful that Svart from GroupDIY was generous enough to post his fix in a thread describing almost this exact problem. He describes a bad electrolytic cap (100uF, rated 25V) next to the daughter-board being the cause of his issue..the same one that was found to be corroded on my unit. Immediately this capacitor was on the replacement list. To be safe, I also added the carbon film 1.2Mohm resistor sitting next to the bad cap as well as the other 82uF electrolytic caps near the output wiring which looked just as bad.

Showing the bad cap and resistor on the supply board

Showing the bad cap and resistor on the supply board

 

Having a list of the voltages carried on the output wires, along with having the labels of said voltages on the main board, I was ready to troubleshoot the board. I read zero volts on every rail against the proper ground/reference wires. The output was in fact dead. I turned to the PWM board and found out the output of the controller chip is pin 6. Measuring that on the oscilloscope revealed the chip wasn’t properly producing its PWM signal.

Highlighting the ground, Vcc, and output of the PWM interface connector

Highlighting the ground (1st pin), Vcc (2nd pin) and output (4th pin) of the PWM interface connector.

 

I also measured the Vcc power input for the PWM chip, which revealed about 14.36V. This particular controller has a minimum start-up supply voltage, which ranges between 14.5-17.5V. I believe this voltage is not being reached due to the damaged cap and resistor on the supply line to the PWM chip.

After replacing the caps and resistor I tested the output lines for proper voltages. The +15V and -15V rails were reading about +16V and -16V, respectively, which I was okay with. The only other DC voltage I was able to measure was the 6V line. The 5V lines were not readable, which was confusing at first. After some reading I found out it was a normal problem with another repair tech. There is apparently a “handshake” signal (carried by the brown wire) between the power supply and main board for activating the 5V line.

Even with that bit of advice, I still wasn’t sure if it was working. I hooked up the oscilloscope and found the PWM controller’s output pin to be operational at about 50kHz frequency.

Showing the output PWM signal on the o-scope

Showing the output PWM signal on the o-scope

With that reassurance, I connected the supply to the main board and the Finalizer arose from the dead! This was a fun one, for sure! It’s evident that this issue isn’t accidental or the fault of the consumer, as this same issue has occurred on multiple units. There must be a design flaw in the supply, maybe improper filtering, under-rated components, missed safeguards, etc. It would be a tremendous move for TC if they were to supply these replacements free of charge, if at all under proper warranty.