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2014-03-09 by <josh.nursing@...>
2014-03-11 by <alpemannen@...>
2014-03-11 by <backshall1@...>
I am looking to solve the power issue completely once and for all in the Poly-800. What are the parts that I can order for repair and replacing existing ones?
2014-03-11 by <josh.nursing@...>
2014-03-11 by <backshall1@...>
Thanks Don, I'd be tempted to do that and sort it out, for now it looks like it draws too much current and I haven't been able to pinpoint the issue.
2014-03-11 by Sami Jumppanen
Hi,
some words about the 78 series regulators amd capacitors.
Regulators are pretty failsafe. I just don't remember if they have overheat protection (check the datasheets). I once serviced a Yamaha ME-30 (the Stevie Wonder - "I just called" has the same sound, I found out :). The problem was a shorted electrolyte capacitor after the 78xx (05 /09 / 12, can't remember). I recall replacing the regulator at first because there was no voltage at the output. But the regulator wasn't damaged. As soon as I spotted and replaced the faulty cap, everything worked fine. So, the 78xx handled output shorting. Also, I learned that a dead capacitor may not break anything else.
After fixing a number of devices by replacing capacitors only, I recommend you always begin with them if it's likely a power issue. Electrolytes, no other types. Medium sized, not the smallest or biggest (depending on the device, there may not be large capacitors). By the numbers: usually 470 to 2200 micro F and from 15 to 63 volts.
Sami Jumppanen
http://netti.nic.fi/~some-e
- SGS2 -
I did a 7805 replacement once, but I didn’t take any pictures and I sold that one a few years ago. I removed EVERYTHING in the +5V regulator circuit, Q1, Q2, Q3, Q15, Q16, D3, D4, D24, C1, C2, C3, R2, R3, R4, R5, R6, R7, R12, R13, VR1. I believe I soldered the 7805 in the holes for Q3, but only one of the three pins was connected where it needed to go, so I cut the traces from the other two pins and soldered a couple wires to where they needed to go. It worked great, but the 7805 got a little warm. It didn’t ever seem to get hot enough that it would need a heat sink though. Wish I had some pictures. It may seem like a lot of work, but I think it was still easier than trying to debug that old regulator circuit. There is no point in touching Q18 on the –5V side until you are sure the +5V is solid.Don BackshallFrom: josh.nursing@...Sent: Sunday, March 9, 2014 1:10 PMSubject: [korgpolyex] Power circuit repair.I am looking to solve the power issue completely once and for all in the Poly-800. What are the parts that I can order for repair and replacing existing ones?
I listed Q1, Q3, Q16, Q18 and a 7805 for now. Anything else I should pay attention to? Any modern parts are welcome.
2014-03-11 by Gordon JC Pearce
> After fixing a number of devices by replacing capacitors only, I recommend... and I generally recommend people scrap equipment that's been subjected to "re-capping" when they bring it round for me to resurrect.
> you always begin with them if it's likely a power issue. Electrolytes, no
> other types. Medium sized, not the smallest or biggest (depending on the
> device, there may not be large capacitors). By the numbers: usually 470 to
> 2200 micro F and from 15 to 63 volts.
2014-03-11 by <backshall1@...>
On Tue, Mar 11, 2014 at 11:42:21PM +0200, Sami Jumppanen wrote:
> After fixing a number of devices by replacing capacitors only, I recommend
> you always begin with them if it's likely a power issue. Electrolytes, no
> other types. Medium sized, not the smallest or biggest (depending on the
> device, there may not be large capacitors). By the numbers: usually 470 to
> 2200 micro F and from 15 to 63 volts.
... and I generally recommend people scrap equipment that's been subjected to "re-capping" when they bring it round for me to resurrect.
I've pretty much only ever seen electrolytics fail in cheap crappy switched-mode power supplies (think Amstrad satellite receivers from the 80s and 90s). Of the rest, I've replaced maybe half a dozen electrolytics that were actually the cause of a fault and only one of them in an analogue synth.
Electrolytic capacitors just don't fail that often.
DO NOT just start ripping them out because you suspect there's some sort of fault. You'll only make matters worse.
--
Gordonjcp MM0YEQ
2014-03-12 by Sami Jumppanen
Good point! I wasn't clear enough. The failed components need to be pinpointed. I didn't mean caps can just be replaced in the hope of getting things better.
The problems are indeed more common in switching mode supplies and especially after 2000. And it's true, old analogue synths are not the usual victims. It is possible to have a cap dead without visible damage, but as Gordon said, blind part replacement is not the way to go.
Sami Jumppanen
http://netti.nic.fi/~some-e
- SGS2 -
On Tue, Mar 11, 2014 at 11:42:21PM +0200, Sami Jumppanen wrote:
> After fixing a number of devices by replacing capacitors only, I recommend
> you always begin with them if it's likely a power issue. Electrolytes, no
> other types. Medium sized, not the smallest or biggest (depending on the
> device, there may not be large capacitors). By the numbers: usually 470 to
> 2200 micro F and from 15 to 63 volts.
... and I generally recommend people scrap equipment that's been subjected to "re-capping" when they bring it round for me to resurrect.
I've pretty much only ever seen electrolytics fail in cheap crappy switched-mode power supplies (think Amstrad satellite receivers from the 80s and 90s). Of the rest, I've replaced maybe half a dozen electrolytics that were actually the cause of a fault and only one of them in an analogue synth.
Electrolytic capacitors just don't fail that often.
DO NOT just start ripping them out because you suspect there's some sort of fault. You'll only make matters worse.
--
Gordonjcp MM0YEQ
2014-03-12 by <bperkins211@...>
2014-03-12 by Gordon JC Pearce
> Doesn't anyone check electrolytic caps with an ESR tester before blindly replacing them? The kind of meter that checks them in circuit..I don't bother to check them with an ESR meter. That can't tell you anything particularly useful.
2014-03-12 by <bperkins211@...>
2014-03-13 by <backshall1@...>
I agree that caps are not a typical failure point in 80's gear.. late 90's to late 00's can be another thing though.. the great cap plague era. I did have a Tascam 4track Porta 01 MarkII that had all 4 preamp's with 10v caps fry(they were in a 9v circuit...) I put new 35v ones in and fixed it right up.
2014-03-13 by Gordon JC Pearce
> Was there any truth to all the hype about bad tantalum caps in the ‘70s? I had an ARP Odyssey a couple of years ago that seemed okay so I didn’t touch them. They all seemed original.I don't think they're quite as bad as people say. They *do* go, but if they do you know about it ;-)
> Don B.