Search found 744 matches

by Yekuku
Tue Jun 08, 2021 2:33 pm
Forum: HELP!
Topic: YAMAHA CS70M PSU repair
Replies: 14
Views: 2103

Re: YAMAHA CS70M PSU repair

You are welcome Hydroblaster.
Please have in mind that I am no pro, all the assumptions are based in my personal limited experience , so I might be wrong in some cases .
I think that i have a few 2sa1015 in my drawer, if you are having trouble finding some , let me know.
by Yekuku
Tue Jun 08, 2021 9:01 am
Forum: HELP!
Topic: YAMAHA CS70M PSU repair
Replies: 14
Views: 2103

Re: YAMAHA CS70M PSU repair

well by comparing TR20 vs TR15, it looks like both power transistors are fed with aprox 22-23V , which rules out the bridge rectifier. Aprox 15V are applied to both transistor bases but TR20 does not output the expected voltage. I think you have a problem with TR20 but also check TR22 as advised pre...
by Yekuku
Mon Jun 07, 2021 9:56 pm
Forum: HELP!
Topic: YAMAHA CS70M PSU repair
Replies: 14
Views: 2103

Re: YAMAHA CS70M PSU repair

-14V is not in spec, the culprit could be TR23/ZD6 but there are chances that another component is faulty and it is causing this voltage drop. What puzzles me is how this is related to the overvoltage that you are getting on the -15V line. Anyways , since you checked all mentioned transistors and yo...
by Yekuku
Mon Jun 07, 2021 7:38 am
Forum: HELP!
Topic: YAMAHA CS70M PSU repair
Replies: 14
Views: 2103

Re: YAMAHA CS70M PSU repair

TR25 and ZD6 act as voltage regulator, to provide -15V to IC3.
You should rule out TR25, what is the voltage on the emitter ? It should be -15V, if not replace TR25.
by Yekuku
Fri Jun 04, 2021 9:48 am
Forum: HELP!
Topic: Service Manuals and Schematics!
Replies: 118
Views: 249979

Re: Service Manuals and Schematics!

Good work blueknob!
by Yekuku
Thu Jun 03, 2021 9:52 pm
Forum: HELP!
Topic: YAMAHA CS70M PSU repair
Replies: 14
Views: 2103

Re: YAMAHA CS70M PSU repair

Hmm, I had a better look on the schematics and the zener is probably for overvoltage protection.
You can measure voltage at its cathode it should be aprox -15V.
On IC3 pin 1 you get -15V ? If yes , can you test TR21 and TR20 ?
by Yekuku
Thu Jun 03, 2021 2:31 pm
Forum: HELP!
Topic: YAMAHA CS70M PSU repair
Replies: 14
Views: 2103

Re: YAMAHA CS70M PSU repair

Hi and welcome.
I think that ZD6 is fried, it is a 15V zener diode , it should regulate voltage to 15V but as it looks like it doesnt.
I have a few other ideas but you should rule out the zener first.
Good luck !
by Yekuku
Mon May 31, 2021 8:24 pm
Forum: HELP!
Topic: Service Manuals and Schematics!
Replies: 118
Views: 249979

Re: Service Manuals and Schematics!

Hi Blueknob, unfortunately I dont have the schematics, I was in the same position trying to repair a midiverb II only to realise that there not any schematics available out in the wild. In my case the problem was a failed DASP CPU, hopefully yours should be ok since the cpu works for a sec, could it...
by Yekuku
Mon May 24, 2021 5:54 pm
Forum: HELP!
Topic: Vintage Korg MS-20 VCO-2 Pitch Control Not Working
Replies: 2
Views: 1145

Re: Vintage Korg MS-20 VCO-2 Pitch Control Not Working

Hi Brett and welcome to the forum. It sounds like a faulty potentiometer, it could be dirty so it is advised to clean it properly and re-check. The pot is 100KOhm (VR2) , you can use a multimeter to measure its resistance or you can read the voltage on the wiper (middle pin) it should vary from 15V ...
by Yekuku
Mon May 24, 2021 8:43 am
Forum: HELP!
Topic: Troubleshooting Jupiter 4 Voice card.
Replies: 18
Views: 6400

Re: Troubleshooting Jupiter 4 Voice card.

Good work Jacob!
If I manage to find the appropriate connectors in order to build the extension card I will let you know.
by Yekuku
Thu May 20, 2021 2:33 pm
Forum: HELP!
Topic: Troubleshooting Jupiter 4 Voice card.
Replies: 18
Views: 6400

Re: Troubleshooting Jupiter 4 Voice card.

Hi Thomas, I have heard about this group, I thought in the past that it would be interesting to participate but I highly dislike facebook and most social networking sites. Actually the only site that I frequently use to communicate with other people is VSE, we used to be a helpful community but unfo...
by Yekuku
Tue May 18, 2021 10:17 pm
Forum: HELP!
Topic: Troubleshooting Jupiter 4 Voice card.
Replies: 18
Views: 6400

Re: Troubleshooting Jupiter 4 Voice card.

Since you have no vco output, CP36 is expected to be sillent, better check CP34 for pulses to rule out the 555.
If there is pulsing, probably the fault could be in IC7 or IC6.
by Yekuku
Wed May 05, 2021 6:09 pm
Forum: HELP!
Topic: Troubleshooting Jupiter 4 Voice card.
Replies: 18
Views: 6400

Re: Troubleshooting Jupiter 4 Voice card.

Well I had another facepalm by looking the VCO schematics, it is a strange design, but thankfully the manual is quite informative. Since there is no extension ,my approach would be to attach wires (with parrot clips) to all critical points , so that you can take measurements while the unit is powere...
by Yekuku
Wed May 05, 2021 1:37 pm
Forum: HELP!
Topic: Troubleshooting Jupiter 4 Voice card.
Replies: 18
Views: 6400

Re: Troubleshooting Jupiter 4 Voice card.

Well , I was not expecting these type of pins..... :facepalm: I have never seen this type of connector, it will be quite difficult to find one. I need some time to research about it . BUT you might not need the extension after all, since noise is working the problem should rely on the VCO core or th...
by Yekuku
Mon May 03, 2021 5:41 pm
Forum: HELP!
Topic: Troubleshooting Jupiter 4 Voice card.
Replies: 18
Views: 6400

Re: Troubleshooting Jupiter 4 Voice card.

Hi Jacob,
is it possible to measure exactly :
1) pin width ( pin diameter)
2) pitch ( the distance between 2 pins)
I am confident that Mouser has what you want, but you need to know the upper specs in order to find the right part.