Yamaha QX3

I recently won an eBay auction for a "spares or repair" QX3 sequencer. It looked bad from the photos, but was very cheap. It turned out to be worse than expected. The case was held together with gaffer tape as and the PCBs were loose inside as almost all of the plastic screw posts had crumbled to nothing. It was also absolutely filthy, but a quick test showed it at least booted.

These used to be screw posts

The keyboard. Filthy and missing a few keycaps

Cherry key switches - and 30 years of crud!

I stripped the case of all electronics and gave it and the keycaps a bath and cleaned up the key frame and PCBs. Copious amounts of epoxy were used to attach new plastic standoffs to replace the broken screw posts. I managed to break one off on reassembally, but the rest seem solidly attached.

New screw posts glued in place

The floppy drive was full of dust, so this was cleaned up and reassembled, before being reinstalled.

Electronics cleaned up and reinstalled

Further testing has found that the sequencer basically works, including the floppy drive, but the encoder is jumpy and only works in one direction and a few of the keys are intermittent. I have removed, opened and cleaned the encoder and the worst of the key switches, but will probably end up doing every switch.

Still to do:

• Reinstall the encoder and check that it now works.
• Check the rest of the key switches and clean as required - or just do them all.
• Replace tact switches - these are the same as the ones in the Juno 106 and I still have about 70.
• Replace the mains flex.
• Replace missing key caps - I'm unlikely to find the correct ones.

Juno 106 tact switches

I've just spent the last hour replacing all of the tact switches on the Juno 106 panel board. I also took the opportunity to remove the remains of the foam dust guards that had become so brittle that they were themselves the major source of dust, and give the front panel a good clean - much easier without the sliders getting in the way.

The remains of the dust guards. They literally fell apart when I touched them.

Dust guards removed, board cleaned up and new tact switches installed.

All of the sliders were still functioning perfectly, so I left them alone. I'm currently waiting for the switch caps to dry after giving them a wash, and will reassemble the synth this evening.

MKS-50 finally repaired

Where did I leave off? Having replaced the BBD drivers and the 4051 that de-multiplexes the control voltages for chorus rate and volume, the noise remained. Replacing the underrated and likely half dead bypass capacitors improved the noise that the BBDs were injecting into the rails, but still didn't solve the problem.

I was on the verge of putting the MKS-50 back on the broken pile when I nudged something near the 4051 and the noise stopped! Initially I expected to find a broken trace or cold solder joint. When I first acquired it, the synth did not respond to MIDI messages due to a number of broken traces. Thanks to all but one of the mounting screws being missing, the PCB had flexed and cracked. The underside is a mess of bodge wires as a result. I had also found and reworked a few suspect solder joints.

Poking around with a meter revealed nothing, but a closer look at the component side found this.

Look closely at the capacitor array. Something isn't quite right.

The corner isn't supposed to be chauffeured and the common pin is missing!

Could this be the cause of the noise problem? The capacitor array is used to sample and hold the control voltages coming out of the 4051. These control the overall volume VCA as well as the VCAs and VCFs for each voice and the chorus rate. Without the common ground pin I'm amazed there weren't more problems. Rather than providing sample/hold the damaged array would capacitively couple all of these control voltages, meaning the chorus CV was being modulated by and indeed modulating filter cutoff, etc.

As the synth is already quite a mess (cracked PCB, bodge wires, missing case lid...) I made a repair horrible hack.

Awful hack, but it works!

As a point of interest, the construction of the MKS-50 is awful. A single layer board with a lot of jumpers, ICs seated at odd angles and some very poor soldering. The case design also makes it difficult to remove the PCB without flexing it. Roland gear tends to be fairly well made, so I'm not sure what happened here.

The MKS-50 lives and sounds great! Next up will be another horrible hack involving a sheet of aluminium and some extrusions to fashion a top for the case.

Juno 106 Resurrection

In my previous post, I mentioned that the 80017A VCA/VCF ICs in the MKS-30 will die at some point. I am expecting this because about two years ago, two of the six in my Juno 106 failed in the space of a few weeks. The 80017A is not actually an IC, it is in fact a "hybrid module" - a collection of SMD ICs and capacitors and printed resistors on a small ceramic PCB, which is then coated in epoxy. It is also notoriously unreliable. The theory goes that either some reaction occurs in the epoxy, causing it to become slightly conductive, or moisture becomes trapped inside it. One solution that many people have had success with is to remove the coating with a solvent. This seems to restore some modules to full health, but not all. Some also require rework due to poor soldering.

After my Juno expired, I removed all six 80017As, intending to give them a bath in Acetone and soldered sockets in their place to make future replacement easier. One of them had already been replaced by a previous owner and the solder pads had suffered. Then I got a Jupiter 6 and basket case Emulator II and fixing the Juno slipped down my list of projects.

Original 80017As. Two are dead and the others are on borrowed time.

On to late 2014 and having spent the last few months on a big project (to be revealed as soon as I get around to writing a post) and repairing the Emulator II (well almost, there are still some issues), I finally decided to tackle the Juno. I couldn't be bothered spending several days stripping the 80017As with no guarantee of success, so I opted for the alternative - the D80017A clones from Analogue Rennascince.

Bring on the clones!

Lots of passives.

One of the many calibration procedures.

Clones installed. Probe on one of 12 test points.

There isn't much more to write really. The clones arrived on a scored PCB panel and installation was simply a case of separating them and plugging them in to the sockets I installed earlier. An hour with a scope had everything calibrated according to Roland's original service manual and I finally have a working 106 again. Many people say the Junos are overrated as they are fairly limited, simple synths. This is true, but they do sound good.

Emulator II Repair part 2

Two days of on/off poking around with a multimeter and pulling each and every socketed IC, de-soldering any capacitor across -15v and AGND and removing a whole group of capacitors that had at some point been (badly) re-soldered yielded absolutely nothing.

The interesting thing is that the earlier repair work had been the filter capacitors on channel 2 and it wasn't the only work on that channel. One of the ICs had been replaced at some point, but typically it was one of the few that were not socketed, which is itself odd as I had thought all E II's had every IC socketed. The replacement IC had been socketed, but it looks as though whoever did the work lifted a pad on the top side of the board and attempted to get the pin in contact with the remains of the track by applying a huge amnount of solder - which ended up shorting two pins - between -15v and AGND.

Previous "repairs" circled

Removing and replacing the socket resulted in me lifting another pad, but I fixed this and the first one with a pair of wires under the board. The short is gone and everything that should be connected is. I'm want to test it, but as I managed to destroy some of the capacitors that I removed trying to trace the problem, I am now waiting for parts. Some of the other ceramic capacitors are visibly cracked and although they have not gone short yet, they likely will in time, so I intend to replace every bypass capacitor on both PCBs - about 150 of them. Oh and that nasty replacement jack just has to go.

Part 3 to follow once I have the parts...

Emulator II Repair Part 1

As mentioned in the last post, I have acquired some new toys. The DEP-3 looks band new despite being 25 years old, works perfectly and sounds great. The early '80s Soundtracs mixer has some dead op amps, including one that appears to have got hot enough to scorch the inside of the front panel. The other item is an E-MU Emulator II. With problems....

I knew the E II was dead before buying it. The power supply had failed (a common problem) and supposedly one of the voices had also expired prior to this. The first thing to do was get the power supply working.

The PSU in the E II was not designed by E-MU. It is an early switch mode supply made by a company called Compower and supplies 5v for the digital circuitry, 12v for disk drive motors (although this isn't actually used in my early E II, they share the 13.4v rail), +13.4v and -15v for the analogue circuitry. The latter two rails are linear regulated after the switch mode supply.

PSU before

and after

Initially the PSU was completely dead and blew the fuse on switch on. A couple of resistors were scorched and one tantalum capacitor had pretty much vaporised. The chopper transistor was shorted and I suspected that most of the electrolytic capacitors were past their prime. As such, I replaced the damaged components and all capacitors. This had no effect on operation - the fuse blew again on power being applied.

I had intended to replace various other aged components later on o make an effectively new PSU and as such had replacements for the various rectifier diodes. This lead me to remove and test the diodes on the mains input on the off chance that they were the problem. Two of them turned out to be shorted! Replacing these solved the fuse blowing issue, but the output rails were still dead. Replacement of the remaining transistors solved this and I now have a working E II PSU.

I still intend to replace the remaining rectifier diodes and also the two linear voltage regulators, but that can wait for another day. Unfortunately I have found an unexpected problem on the E II itself - a short from -15v to ground on the (huge) output PCB. This board is covered in tantalum capacitors and these are my initial suspects. Time to dig out the desoldering gun again...