Emu Emulator II

Emu Emulator II

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. The harness was in a sorry state where it connected to the power supply, and a new connector was fitted. Continue reading

Moog MiniMoog

Moog MiniMoog

Moog MiniMoog

The owner of this unit was having trouble finding someone to repair its dead oscillator and other issues because it had a home-brew CV interface installed that was not working. He had taken it to another repairer who would only work on it if the mods were first removed, but would not take on the mod removal task. It therefore came to me for mod removal and repair, and thankfully I had another MiniMoog in that I could compare the mod and original wiring with. Continue reading

Arp 2600 with bad VCO

Arp 2600 with a bad VCO

Arp 2600

This just came in with “squirrelly” keys, and VCO 2 was drifting badly when warm. The keyboard contacts were cleaned, and VCO 2 was checked with an oscilloscope. The VCO was found to have drifting frequency output, but stable inputs. The 2600 had sealed VCO’s (these early modules were encapsulated in solid epoxy, later ARP ones had an epoxy sealing layer and can be opened and repaired) so an aftermarket replacement was ordered from CEM. The replacement part arrived after some months and was duly fitted. The keyboard contacts were cleaned, and the unit set-up per the service manual.

via This Old Synth – Vintage Analog Synthesizer Repair Portfolio Page.

E-mu SP1200 Drum Machine

E-Mu SP1200

E-Mu SP1200

This was purchased by the customer some time ago, and he had stopped using it due to boot problems. It had sat in storage for some time and gradually degraded. It was a missing large touch-pad button, plus the boot diskette had been lost. Without the diskette there was no way of finding out what else is required, and the customer went off to find one.

A boot diskette was finally sourced, and after many attempts it finally booted. The boot issue needed to be addressed, and it showed a need for pad button switch cleaning. The LCD back-light was also out. Continue reading

Gleeman Pentaphonic

Gleeman Pentaphonic with standard case

Gleeman Pentaphonic with standard case

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 Gleeman Pentaphonic bad connectorcustomer was delighted to have his treasure back working as good as new!

Roland Jupiter-8

Roland Jupiter-8 in for a service

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!

Gleeman Pentaphonic

Rare Gleeman Pentaphonic with see-through case

Rare Gleeman Pentaphonic with see-through case

This is the see-through model, 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.

E-mu Drumulator

E-Mu Drumulator

E-Mu Drumulator

This E-Mu Drumulator was 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.

via This Old Synth – Vintage Analog Synthesizer Repair Portfolio Page.

Moog Opus 3

Moog Opus 3

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.

Roland TR-909

Roland TR-909

Roland TR-909

Three of these have come in recently with missing sounds or crackling sounds. Two components seem to be failing with time, M5218AL’s and 2sc2603 transistors. The 2sc2603 transistors are a common crackling sound cause (use something like a BC547 but watch out for different pin-outs).

 

 

DeMC4558 on a SIP carrierad 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 as can be seen on the picture here.

via This Old Synth – Vintage Analog Synthesizer Repair Portfolio Page.