Tag Archives: emergency room

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.”