Monthly Archives: March 2012

Gleeman Pentaphonic

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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

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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

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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

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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

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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

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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.

Realistic Concertmate Moog MG-1

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Realistic Concertmate Moog MG-1

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 Moog MG-1 Circuit Boardthin sound, crackles, and the contour was misbehaving. A mod had been wrongly applied which injected earlier audio onto the volume control Moog MG-1 Keyboard and second circuit board 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.

This Old Synth Blog

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This Old Synth was created out of our AmpTech guitar and amplifier service with a specific focus on vintage analog synthesizers (preferably the ones with knobs on!) and is now 99.9% of what I’m doing in the shop. More and more vintage analog synthesizer keyboards and drum machines were being brought in, especially Moog variant’s; with MiniMoog’s being my favorite. It seemed like the other repairers were either too backed up or were having too much difficulty fixing certain vintage keyboards, so I stepped up!

To date the repairs section of the site has been the repository for repairs information, here we move to a more real-time publishing concept. I also registered the business in the City of San Jose, CA as it is where I am located.

To contact me email: chris@thisoldsynth.com