Korg Polysix synthesizer

[redwire]

Re: Korg Polysix synthesizer

I think you're just making sure the power supply regulates and doesn't collapse under load. I'd just use car lights #194 (~0.3A) as a dummy load for a quick test.

The +/-15VDC regulators have current-limits about 1.2A, and the 5V regulators 0.6A so I wouldn't load heavier than that.
Note +/-15VDC regulator outputs feed the +/-5V regulators input. So a 0.6A load on the +5V and 0.6A load on the +15V is maxxing it out = 1.2A load on the +15V reg.- they add up.

Output voltages running (service manual) some are tight:
+15.000V +/-0.05V
-15.000V +/-0.3V
+5.000V +/-0.01V
-5.000V +/-0.01V

[stj]

Re: Korg Polysix synthesizer

not at the same time, you will overload it
maybe after the 15v is checked.

[SteveNielsen]

Re: Korg Polysix synthesizer

Ok, thanks Budm. Mine measure 21 ohms cold but they're 130v. That will still work and draw around 1/2 amp.

Related and interesting, earlier stj advised me not to use halogen bulbs for current limiting on the ac line because the cold resistance is too low. However I have some 40w 120v halogens that measure 21 ohm cold as well. I think I ought to be able to use them as a load for this as well.

Should I dummy load the 5v outs too?

[budm]

Re: Korg Polysix synthesizer

230v lamps are not that common. I will get it worked out here soon and let you know.

I forget that you are in the US. Use 40W lamp then, it has about 30 Ohms cold resistance, you can verify that with the meter.

[SteveNielsen]

Re: Korg Polysix synthesizer

230v lamps are not that common. I will get it worked out here soon and let you know.

[stj]

Re: Korg Polysix synthesizer

dont people get "swat"'ed for owning those now!

[budm]

Re: Korg Polysix synthesizer

You can use 100W 230V LAMP as the load, the cold resistance is around 30 Ohms, you can easily check the cold resistance with the meter.

[SteveNielsen]

Re: Korg Polysix synthesizer

So just load one side at a time? I can do that. Better than nothing eh?

[Agent24]

Re: Korg Polysix synthesizer

Just those two? Might be good enough. Put both in parallel and on the 15v rails should draw about 200mA. Should be good enough to load the transistors and warm them up to see if anything weird happens. Unfortunately you can only test one rail at a time with that though.

[SteveNielsen]

Re: Korg Polysix synthesizer

Nope. I've got a 100ohm 10w and a 560ohm 5w, that's as close as I can get without ganging a boatload of 1/2 watts together, and I'm not sure I've got enough of workable values of those.

[Agent24]

Re: Korg Polysix synthesizer

Got any 160-200 ohm or so 5 watt resistors? At 17v, Each one will draw about 100mA and dissipate 1.6 Watts. Start with one and add add more in parallel to increase the load.

[SteveNielsen]

Re: Korg Polysix synthesizer

No shorts on any of the wires. All the solder joints look ok on the board.

I don't have suitable dummy loads to use. If I shoot for a .5 amp current that will be 7.5 watts and 30 ohms at 15v. Don't have any automotive bulbs.

[SteveNielsen]

Re: Korg Polysix synthesizer

I think that must be an unintentional paste at the beginning there Budm

Your explanation makes sense though, thanks.

Redwire, remember this was a no load test. I'll be doing some loaded testing and the other suggestions and keep you all updated.

Thanks to everyone for your interest and help so far. You folks are great.

[budm]

Re: Korg Polysix synthesizer

"Okay, Pos lead on anode, neg lead on neg leg of C102 reads 117V AC" That may be because the + has more load than the - supply. The +/- power supplies are tracking power supply, so if one goes up or down in Voltage it will track each other.

[Agent24]

Re: Korg Polysix synthesizer

Playing with trimmers of any kind is a bad move until you rule out other problems.

R13 or R14 or R17 could have drifted. The thermistor TH1 could be bad. Check values and solder joints on all of them.

[redwire]

Re: Korg Polysix synthesizer

... I measured +17vdc, -17vdc and 5vdc at the output test points...

Wait, it's a +/-15VDC power supply, not 17V? Time to turn the trimpot?
There's also +/-5VDC outputs; four outputs in total.

[Agent24]

Re: Korg Polysix synthesizer

Since the original fuses are 1A, don't go beyond that. Half that at 500mA per rail or so is probably a good start.

[SteveNielsen]

Re: Korg Polysix synthesizer

I wonder if the fuses should be slo-blo type due to that 4700uF filter cap has lost of inrush current.

Nothing I see indicates slo-blo but that brings up a question I have in mind. Why is there a 4700uF on the + input and a 2200uF on the - input of the regulator chip (IC2)?

Because some people are silly and they were probably running it at maximum volume for long enough to blow the fuses.

Would still be smart though to put some dummy load on it and run it for a while.

I would not doubt that fuse blowing scenario at all. Looking at the poor thing it has obviously been through hell. Knowing who it came from only casts more suspicion of abuse. Ironically, her father was an electronics tech.

I agree on the dummy load thinking. I just have to see what I've got around here for dummy loads that could work. I think I'll need 3 loads, one for each; -15v, +15v, and +5v. I don't know how much current draw each voltage line should be tested at.

[SteveNielsen]

Re: Korg Polysix synthesizer

Well, I do have a heat gun That'd be overkill though I think.

I don't think I've got any auto bulbs around, but I'll have to look. I've got several power resistors of various values though up to about 5k I think.

The wires are all routed clear of anything that could pinch them but I have not checked them for shorts. I could measure at the test points on the PSU and plug each cable in and check that way, if there's a shorted wire I should be able to narrow it down to a specific bunch that way. Thanks for the good suggestions.

[Agent24]

Re: Korg Polysix synthesizer

Edit: I think I blew the fuses before from having one of the caps reversed polarity. If the PSU is ok then the question in my mind is why did someone jumper the fuses?

Because some people are silly and they were probably running it at maximum volume for long enough to blow the fuses.

Would still be smart though to put some dummy load on it and run it for a while.