Portfolio of Repairs
I'm at the point now where the number of vintage synth
and amp repairs undertaken means that I cannot keep this log up to date. I
hope that the information here has helped other repairers and I welcome
their contact with questions.
I added a Blog to make adding repair data easier in the future.Moog Variants
Realistic
Concertmate Moog MG-1 Restoring this mini synth was a long
process as the electronics in it is highly interactive and tends to mask
the root cause. A previous repairer had replaced all of the sliders and
switches, along with cleaning all of the goo from the control panel where
the original foam had deteriorated. The switches and sliders still needed
vast amounts of switch
cleaner to get them crackle free. Cleaned the
keyboard contacts also. The symptoms were then a thin sound, crackles, and
the contour was misbehaving. A mod had been wrongly applied which
injected earlier audio onto the volume control
rather
than aux-in; removed this mod. Transistor Q28 which is associated with the
audio out (LM3080) was causing the crackling and very low sound from cold.
The contour issue was the LM741 (U8) which is a summing amp. Thankfully
Anchor Electronics had some of these obsolete LM741's.
Realistic
MG-1 Moog This unit needed the sticky foam removed, and all of
the switches and sliders replaced (because the foam ruins them). I ordered
a replacement sliders/switches/slider & pot caps from Technology
Transplant. I was concerned as these parts ship from China and
communications were non-existent, but parts turned up within a week and
were fine. This unit was in
excellent condition and after new parts and knob hardware were fitted it
was like new. Customer was ecstatic, except Technology Transplant supply a
bright blue led that is too bright for use in a darkened concert hall. I'm
now fitting green, yellow, or red leds! Sorry for the bright blue Lance!
Realistic
MG-1 Moog This unit also had its sticky foam removed and new
sliders and pots fitted. It had a number of electronic issues to be
resolved, many of which I'm convinced are due to sticky foam sitting on
components - is this stuff conductive?
One
of the poly chips had failed and luckily some folks in
the
UK have recreated the chip. The circuit board had a fracture through the
tracks which were bridged. The trans conductance amp (CA3080E) had failed,
and there was a hard to find intermittent fault in the VCF (CA3084). After
this it was reliable and works great!Moog Rogue This one was not working after an attempt to move the wall-wart on-board. All issues resolved.
MicroMoog The touch control
was the issue here.
Parts were not available. The control was rebuilt and its connections to the main unit had the bad solder joints remade. Tested
and working fine.
Moog Opus 3
This unit is nicely
laid out on the control panels in order to make it easier to understand,
in fact, even I could understand it! It had two main
problems: The chorus
section was not working due to fractured tracks on the circuit board, and
strings were not working due to a control chip (CD4070?) failure. Moog Opus 3 A second unit came in with a severe case of deteriorated foam having ruined all of the sliders and switches, along with other issues. A deep clean was performed, all sliders and switches removed, board washed, and then re-populated. The other issues could then be isolated and repaired. I believe the foam is getting conductive and destroys chips, especially the CA3080E; best not to power it on when you find one with the foam issue and to get it cleaned up first.
MiniMoog This was a flea-market purchase, WOW! It was in a sorry state. The keys
were sticky and
wavy, power cord was rotten, it looked dreadful, and did
not work to boot! The cabinet was tidied, new keyboard bushings installed,
power cord replaced, unit re-cap'd,
oscillator resistors
balanced, all
connectors, pots, and switches cleaned. It seems that his unit
was riddled with electronic, connector, wiring,
and component issues. All
issues were resolved and the unit was set-up using a scope and frequency
counter. It sounded great and I was sorry to see the owner take this
keyboard
away OK; on to the next one!
MiniMoog The owner of this unit was having trouble finding someone to repair its
dead oscillator and other issues because it had a homebrew CV interface
installed that was not working.
The
bad CV interface was removed and painstakingly all wiring was put back to
standard. The
oscillator
was then repaired, along with all other issues found during test. The unit
was re-cap'd on the boards and power supply; followed by a set-up using a
frequency counter and scope for accuracy. Customer tested it and is
delighted with the results.
Moog Taurus II No sound due to a bad filter chip, and a
service carried out.
Moog Sonic Six This one needed the key deck straightening
and re-bushing. A number of switches and sliders were broken or seized,
and getting parts to fit this was difficult to say the least. Returned to
customer fully functioning; and he gets to play a rare Moog variant now.Moog Taurus 1 General service that concentrated on the footswitch contacts. New rubber feet were fitted to stabilize the unit, an a broken track that prevented the glide control from working was repaired.
MiniMoog This unit had
been modified by adding a CV interface for which there was no
documentation available, and then mods pots and switches added on top of
that. It had a dead oscillator 3 and other repair folks had refused to
work on it due to the mods and the fact that somebody in their infinite
wisdom had once cut the wires from 3 connectors and badly hard wired the
boards in.
What
a mess!!!! The hard-wiring was undone, connectors sorted out and machine
got to the point where it could be fault found. The oscillator was dead
due to a bad 741 and CA3046. The unit was set-up but osc 3 could not be
tracked. This was fixed by fitting a missing capacitor. The unit was
re-cap'd, resistors checked for balance and then set-up using a scope and
frequency counter. All was well. The customer tested it and found basic
operations spot on, and the mods provided a WOW factor. A humble DX100 was
used to drive the mighty MiniMoog as a final test of the CV interface. OK,
next!
MiniMoog Musonics This early unit (#242) needed some
further work after another tech had worked on it. The keyboard had been
re-bushed, but the bushing supports had not been straightened, which
coupled with some badly stretched key return springs had left it
un-playable. This was resolved, and once the set-up was completed (it had
been tuned from C on the far left when in fact the first key is an F!) it
played great.
More and More Moog Repairs Moog repairs for me have become the sweet spot.
A number of MiniMoog's have passed through other repairers and ended up
here, and when they left me they were fully working and resulted in happy
customers. The MiniMoog is the most popular Moog that comes in for repair;
most are resolved by new keyboard bushings, re-cap's, and deep
cleaning of
contacts, switches, and potentiometers. I'm searching for a scruffy
MiniMoog that I can use to repair and test customer cards such that they
can send me the plug in modules rather than a complete machine. Other Moog
keyboards that have come in include the
Moog Source and
Moog Prodigy, oh, and then
there is the mother machine: a 1969 Moog Modular System 55 that
was
scored in Seattle and needed restoration after being powered off for 20
years as every pot and jack seemed to emit loud crackles, and the keyboard
was in a sorry state. The case was cleaned and treated
with lemon oil. The keyboard needed new bushings and the keys were cleaned
and remounted onto
straightened
and leveled hardware; cleaning all of the keyboard contacts got rid of
squirrelly keys and the keyboard then tracked. Each module was then
cleaned, re-cap'd, all pots were cleaned (which meant opening some 96
sealed pots!), and jacks and switches were cleaned. This clearly took a
lot of time and careful attention to detail, but when we fired it up
afterwards it was all worthwhile!Keyboards
Here is a vintage (1983) Yamaha DX-7
synth
that came in for repair with the symptom "powers up but no audio output".
The issue was with the +15 regulator in the power
supply. I fitted a new regulator and a happy customer was reunited with
it.
Arp
2600 This just came in with squirrelly keys, and a drifting
oscillator 2. The keyboard contacts were cleaned, and Osc 2 was scoped. The oscillator was found to have drifting output but stable inputs. The 2600 had sealed oscillators so an aftermarket replacement was ordered from CEM which arrived after some months and was duly fitted. Unit set-up and returned to customer. 
I discovered an 80's
Ensoniq SQ-80 synth in Guitar Showcase
that was being sold "as-is" as it had so many problems. There is renewed
interest in this synth as it is an analogue to digital transitional
product. The first job was to clean it inside and out, there was a fair amount of corrosion on
the screw heads, thankfully an easy fix. Cleaning out what looked like dog hair was not so pleasant, and it meant a complete strip down of the keyboard was required. This synth suffers a number of stock
faults, and this one had them all:
Back-up 3v lithium battery had expired,
volume and data entry sliders had failed (50k linear, available from Mouser),
the bridge cable between the keyboard halves had disintegrated and had to be replaced,
and the floppy cable had been trapped and a screw had cut into it. This
keyboard is now rock solid.
Ritm-2
Russian Synth This was badly damaged by a transformer that broke
away during transit and smashed a number of items. Rebuilt power supply,
converting it to 120V. Repaired the damaged components, crafting switches
to fit etc. This was difficult as the schematic was in Russian, and
components were not available. 
E-mu
Emulator II This sampler workstation from the early 80's has the additional (to the 5 1/4) 3
1/2" floppy drive installed and this floppy was giving errors. Reseating
cables cured that. The big issue here is that without the boot floppy (and
you need an old Apple II to create the floppy) you have no way of booting
this device. Also 3 1/2 HD media will not work, you have to find old DS-DD
media.
Managed
to create a copy of the 5 1/4 disk onto 3 1/2 and boot off of that so
should be safe now! Also the small square button for disk utilities was
missing. You can get the switch from Digikey; I found a similar one in
Anchor Electronics on Walsh in San Jose and fitted that.
Emu Emulator II This one had a bad power supply, and the customer
had been trying to fit more modern replacements. Re-soldering cold solder
joints bought the base power supply back to life on the bench, and when
fitted to the Emulator the root issue was shown to be a shorted tantalum
capacitor on the input to the -15v regulator
. This unit has a lot of corrosion and shows memory issues; next move is
to clean the sockets with isopropyl.
A
Trio of DX-7's There are a lot of DX-7's out there, and age and a
lot of use make these a common keyboard to come in for repair. These were
all 1st generation (brown casing) machines, and two of them had Grey
Matter enhancements. Repairs were a mix of new battery, bad keyboard
contacts, and
poor volume/data entry sliders. It isn't uncommon to end up with no sound
following a battery repair or remove/replace the Grey Matter card
(corrupts ram). Go through the voice initialize process in the Grey Matter
manual and then reload the patches; this should put things back right!DX-7II I have repaired many of these. Most just need a new battery, or maybe a broken key (same type as a DX-7). This is a very reliable variant of the DX-7 and has floppy storage too.
DX-100 I must have repaired 20 of these. Consistent issues are corroded power jacks. Dry jointed/cracked pcb connections to the power jacks. Expired batteries (OK, this is not a DX100 issue per-se). Broken case posts at the inner front of the keyboard (rigidity of structure impacted). Broken keys. This keyboard is small and does not seem to be built to take the rough handling it gets. Great DX sounds from a small portable package though!
Roland
Juno-D This keyboard had a growing plague of dead & intermittent
keys. The keyboard was stripped and keys removed which revealed 5 rubber
bubble strips held by small rubber prongs and sticky tape. Removing and
replacing these strips without damaging them is a slow delicate operation.
I cleaned both the board contacts and the black contact area inside the
strips.
Four
of the sections showed a small amount of cleaned off residue and worked
after re-assembly, the right hand strip did not and there are a couple of
not so good keys still there (working but not fully functional). Customer
will try it out for a week or so to see if things improve/degrade. Next
move is to try to obtain a new rubber strip for the RHS and fit that.
Sequential Circuits Split-Eight
This keyboard had no
sound
output. If you turned the volume full on you would hear "motor boating"
which leads you to the power supply or grounds. The power supply negative
rail to the main board and rest of the system is through a single pin on a
connector, and the pin had come apart. Pin replaced and all is now well!
Roland
Juno-60 This came in with every 6th key dead. The problem was
traced to one of
the VCF's. I found an IR3109 VCF chip and finished
this off. While working on this synth I
found that other keys were intermittent and performed a keyboard contact
clean in order to resolve this.
Korg M1 This came in as a dead unit and was in a grimy, previously
worked on (missing screws, missing hardware, partially unsoldered chip,
broken joystick (parts missing too), and a missing small round key top).
The power supply was repaired (bad
switching transistor and open circuit resistor) and the casing was cleaned
(plus chip re-soldered).
The
keyboard now works and all of the stored sounds were still there!
Unfortunately a replacement joystick could not be found but the unit
worked perfectly otherwise and is now with a new owner.Korg M500 MicroPreset This was a very tired keyboard, and had lots of dirty contacts in the switches. Once the contact issues were resolved and a bad LM324 in the voice circuit was replaced all was well.
Roland SH-101 The last one that came in with some dead keys had a cracked circuit board under the keys, I'm amazed that this damage could occur without breaking any keys (skillful playing I guess). It also had drifting tuning due to a bad power switch; this had be scratching my head but it is in fact a common problem on this keyboard.
Korg 01/W This is a nice looking keyboard that came in for a backlight
replacement as the LCD is dark. Part took forever to come, not
satisfactory! Note that
EVERYTHING has to be taken out layer by layer t
o get to the LCD; this
takes around an hour and it will take another hour to fit the backlight
and put it all back together. The customer asked about updating the
firmware and I passed on the advice I read online that as he is the original
owner he can request it for free from Korg. I eventually found the latest
(#62) firmware and fitted and tested it.Octave Kitten Lots of connector, pot, and contact issues resolved.
Gleeman Pentaphonic This was a see-through one, and reportedly
there were only 20 made. This one had failed solder joints in the
power supply, and on the front panel. The keyboard needed re-bushing, and
there was an issue with every 6th key being louder, and issue with the
switching chips also sending audio through the sequencer. We
managed to swap chips around so we could use an unused chip section, and
are trying to find another chip. The keyboard is being used without the
sequencer for now.
Gleeman
Pentaphonic this one had been killed by another repairer during a
battery replacement. Thankfully the unit was not "blown up", the issue was
a failed solder joint on a power connector that caused a connector pin to
fail, and the wire connected to that pin to fail. Not too difficult a
repair, but it does cause concern about "techs" changing batteries but
unable to do anything else and putting a rare and valuable keyboard at
risk. I also re-bushed the keyboard and the customer was delighted to have
his treasure back working as good as new!
Roland SR-505 A number of these have come into the shop. I'm
seeing power supply faults, corroded connectors (especially ones causing
the bass keys to fail), and bad capacitors. Great sounding string synth.
Juno
60
This keyboard had "sticky keys". The issue was a previous
repairers fix which was to drip epoxy
in and lock the bad key to the one next to it. Replacement key obtained
and fitted. The keyboard contacts also needed a clean. Keyboard restored
to health.
Roland
Juno 106
A number of these have come into the shop and for most
of them it is a 80017a VCF issue. Roland put 3 chips (including the 3109)
and supporting components onto a module, then covered it with a moisture
sealing coating. There is a belief that the coating was required in order
to protect surface
mounted resistors from humidity change in order to
stabilize their value, and that this coating becomes conductive after 20
years or so. The only source of replacement parts is through chip pulls
from scrap machines, and they are rare so costly. A typical symptom is a
hanging voice, and/or crackling. I recently invested in a special
de-soldering station in order to get these chips out cleanly. The keyboard
here was purchased on Craigslist by the customer for a good price but when
he got it home he found it crackled badly, and a voice was hanging (you
can isolate which of the 6 voices it is by putting the keyboard in test
mode). For this one it was not obvious which chip it was but careful
testing showed it. A replacement was obtained and fitted; all seemed well.
After 3 hours of just sitting warming on the bench another chip started to
crackle and had to be replaced. Speaking with the chip vendor this
scenario is not unusual. The keyboard was not such a deal now that the
cost of two replacement chips is factored in but the customer loves it and
will get good use from it.
Roland SH-5 This unit came in with two issues, LFO-2 not modulating with led dark, and pitch-up control not smooth.
The LFO came back to life when the CA1458 (same as a LM1458 or 4558) was replaced. The pitch control is metal and
some wear had taken place; this was greatly improved by stripping, cleaning, and lightly greasing the assembly. Both oscillators needed tuning and scaling (thankfully you can access the controls from the front panel), and once tweaked it sounded great.
Roland
Jupiter-8 The customer had just purchased this keyboard and
wanted it serviced as there
was
a lot of lint and slider gasket debris in the controls. The work order was
to strip out the old gaskets and replace them with felt, clean all old
debris from controls and circuit boards/case, lubricate the controls, and
replace the battery. To back-up the patches
prior
to battery replacement (3.6v Lithium from Jameco) I brought an old
cassette
player into service, and it worked like a dream! Thick (3mm?) foam of the
type originally used could not be found, so we went with the most rigid
felt that could be found. Felt is not as rigid as the foam, so a lot of
double-sided tape had to be put around the controls to hold it. I
would
not recommend felt due to its lack of rigidity
and
shedding, but until a better material can be found then we are stuck with
it! The unit looks really nice, and the customer was delighted!
Alesis QuadraSynth Plus Piano This came in with the symptoms of bad
smell, smoke, and losing
patches. A sniff test led me to the 5v regulator
where the soldering had failed. Removed the regulator and cleaned the
area. Reassembled using
fresh thermal grease and tested all patches OK. Thankfully the spiking
power does not seem to have done long term damage.Electric Organs
Rheems
Mark VII The reported issue was a disintegrating power lead that was no longer
un-pluggable, and a constant vibrato noise in the background. I also found
the right hand octave had intermittent key
contacts during test, and volume was low. This is a seriously old piece of
equipment which requires a special optical pedal to work correctly.
Searching the web I
found that
this could be resolved by putting a jumper in 2 pins of the pedal socket;
doing this puts both bass and regular outputs out of one socket, restoring
full volume. You do not get any volume control of course and one
switchable function is no longer available.
The old power cable was
removed as it had been hard wired in and the cabinet was routed to take an
IEC power socket. This is nice
and neat now. Cleaning the RH keyboard contacts
requires
the internal mounting board be removed, along with the keyboard. You
eventually get access to small canned module with the contacts inside. All
very fiddly, and a lot of careful cleaning was required to restore
operations. The
constant vibrato noise was due to a microphonic pre-amp/vibrato module.
The input resistor is wirewound and a leg had fallen off, and the power
rail copper tracks on the PCB
had fractures
which were bolstered by tacking wire runs along the tracks. This work was
carried out beneath the card so it retains its vintage look from above
inspection. Noise issues were resolved and after some pot and switch
cleaning all is working well.
Korg
CX-3 Organ
A customer purchased this keyboard which had dead and
intermittent switches, and a number of dead keys. Several passes of
cleaning keyboard contacts had to be made in
order
to get reliable keyboard operation. The dead switch was a "dry joint"
which needed to be re-soldered. The intermittent switches were resolved by
disassembling
two of the option stitches and replacing the micro-switches (a LOT of
these fail on vintage gear from many vendors, I just replaced 14 of these
switches on an Akai MPC2000 as an instance of this).
String Driven Things
One day Andrew brought me a Wurlitzer to repair, and it needed mechanical as well as the electronics' repaired. Why I asked, "cos you are good with your hands" was the reply.
Wurlitzer
200
The keys had a wave only sailors could love, keys stuck,
hammers did not sound, the electrics were bad but the cable connector was
obscure and lost so who really knew. I researched this and read that the
service manual stated a mixture of
Naphtha and silicone could be applied to clean and lube the hammer joints,
but don't soak the wood. I made
the
mix and purchased an injector bottle, then took every one of the hammer
mechanisms off and lubed it... this was a SLOW process and you had to be
careful not to wet the wood, so every actuator was removed.
The
unit was the set-up and was mechanically excellent. The next job was to
rout the cabinet for an IEC power connector and fit that. The electronics
were re-cap'd and the whole
thing
finally cleaned and set-up. Visitors to the shop had previously hit a
couple of notes and shrugged their shoulder and walked away, now they sat
and played it. The owner played it for 30 mins and then took it away. I
now understand why Super Tramp used a Wurlitzer in their songs. The
Wurlitzer expanded my skills, and now folks are bringing me Fender Rhodes
and Hohner Clavinet's.
Drum Machines
E-mu SP1200 Drum Machine
This has a missing large touch-pad
button,
and no boot diskette. Without the diskette there is no way of finding out
what else is required. Replacement dynamic pad buttons obtained from
Forat, and a boot diskette was sourced.
Two more switches were replaced
along with the LCD backlight and LCD cable (fell apart due to age). The
grounds were cleaned and power supply heat-sink was enlarged. One slider
was replaced as it failed final test. The final
problem was with memory corruption and crashes after the floppy drive was
accessed; this unit had previously been sent to a specialist for this
issue... there is a one shot 74LS221 that times access and replacing this
chip and selecting a closer value timing capacitor made this SP1200 a
solid performer again.
Roland
TR-909
Three of these have come in recently with missing sounds
or crackling sounds. Two components seem to be failing with time,
2sc2603 transistors are a common crackling sound cause (use
something like
a BC547 but watch out for different pin-outs).
Dead sounds tend to be the
M5218AL IC's. These are SIP's and getting rare. I have had great success
with mounting a 4558 DIP on a SIP module.
Emu Drumulator Blowing fuses due to a shorted capacitor in the
mains power input. This unit has both a midi interface and switchable
sound banks.
Emu Drumulator Blowing fuses due to a shorted tantalum
capacitor in the power supply. The power supply held the CPU in reset
following this, and a CA3086 transistor array was replaced to resolve
this, along with the related FCO from EMU. One switch was missing and replaced,
the switches were cleaned, OS 3.0 was installed.
Korg
Rhythm 55 Hum on sounds and weak sounds. The 10uf capacitors were
leaking,
and
some had done damage to the circuit board. All 10uf and 1uf capacitors
from the same manufacturer were replace. Should be good for another 20
years!
Univox
SR-55
Some sounds not working, this was simple but delicate work.
The cable-form seems too
heavy for the fine wires so with years of the devices moving around the
wires fracture. Strip and re-solder, then put the unit down gently!
Oberheim
DX All switches opened up and oxidization cleaned off. One of the
7 segment displays failed and was replaced. A new battery and general
clean had this unit restored. 
Roland
Drum Machines
The full range from Roland seems to have been through my door including the TR-808, TR-707, TR-606, and
many TB-303's.
PAIA
5700 I have worked on a number of vintage PAIA units, Here is a
5700 Drum Synth.