Power problems - Yamaha EL 90 from Japan

[echan42]

I'm repairing this Japanese (100v) Yamaha Electone EL90 with no sound, once I popped the lid it was clear what had to be done, since the damage was quite evident.
After cleaning up the PU board and replacing the bridge rectifiers, the IC next to them, and all 3 voltage rectifiers, and the caps and rebuilding traces that where toasted, I realized the transformer wasn't looking too good.
Seems like enamel coating leaking from the core, this may be the issue that cased all the trouble on the PU board, but I wouldn't disregard leaky caps had a hand in this too.

I've read the Service Manual up and down a few times and I still don't know what values I should be expecting from the transformer or what I could replace it with, I don't want to plug the transformer in to my PU board and run into the same components burning up again.
If anyone has an EL90 and a multimeter I'd truly appreciate if they could take the time to probe the outputs voltages from the transfomer.

Any ideas where to take it from here?

Service manual:
https://elektrotanya.com/yamaha_elec.../download.html

[Admin]

Are you sure that's enamel from the windings, and not the varnish used on the transformer plates drying out and flaking off? The transformer may have gotten hot when the PSU failed. It's possible that it's still OK.

From the diagram it appears that the PSU provides 5 volts and +/- 15 volts, and another voltage which isn't visible on your photo. If the transformer is indeed bad, you may have a problem finding a replacement, even if you can figure out what its output should be. It might be easier to find a suitable off-the-shelf PSU with the necessary voltage and current outputs to replace what's currently there.

It appears from your photos that some of the power supply wiring is frayed and in danger of shorting. Regardless of how you deal with the PSU, you'll want to replace those wires.

[echan42]

Are you sure that's enamel from the windings, and not the varnish used on the transformer plates drying out and flaking off?

You might be on to something there, there's residue all over the transformer but none where the transformer was mounted inside the organ, so I guess it could well be varnish.

If the transformer is indeed bad, you may have a problem finding a replacement.
It might be easier to find a suitable off-the-shelf PSU with the necessary voltage and current outputs to replace what's currently there.

I thought so too but the PU board is also the amplifier and I generally think it'd be simpler to get a few transformers, one for each secondary winding in this transformer, and fit them neatly since this organ is so spacious.

t appears from your photos that some of the power supply wiring is frayed and in danger of shorting

I think that's residue from some foam I had to remove because it was gross, I'll double check in case I missed something.

Thanks for such a quick answer, this community is great!

[Admin]

I thought the yellow wire at the bottom of the transformer picture looked nicked and frayed.

[echan42]

Checked the yellow wire and thankfully it's in good shape, thanks for looking out for shorts, that would be a disaster

[echan42]

Quick update!
After re-capping, trace repair, and a general clean-up the board is behaving, I have it hooked up to the questionable transformer on my workbench.

I've taken some precationary measurements before installing the board back in the organ since I'm still not convinced the transformer is playing nice, and here's my results.

All outputs from the board seem up to spec except for CN12, wich strikes me as weird since CN12 and CN13 share a node and CN13 checks out fine.

[Admin]

I'd be concerned about CN12 if you're measuring 11.5 volts. The diagram is a little blurry, but it appears that the capacitors in that circuit are rated for 10 vdc, but maybe it's 18 vdc, in which case you're OK; however, the fact that these terminals are labeled as 7 makes me suspect that the output here should be 7 vdc. R181 should be dropping the voltage down.

CN 13 is fed from a voltage regulator which would correct for any over-voltage situation.

[echan42]

Quick response as always! I'm definetly worried about CN12 wich is way above the 7vAC the organ is expecting.
Luckly when I re-capped the board I thought ahead and replaced all the caps with the same ones but up-rated a few volts, so we're good.
I think this pretty much confirms the transformer coils are bad since after my repairs I can't say the board is at fault anymore.

When rectifing ac the resulting dc is Vdc=sqrt(2)*Vac minus the diode's voltage drop, so Vac=7/1,41=4,96, so is it safe to assume the pins 1 and 2 (the orange wires) are ment to carry 5v more or less?

I'm considering replacing the coil for 3 coils one for each voltage or either taking your route and finding a suitable off-the-shelf PSU, wich I've never done before and I'm slightly intimidated by the idea, but I'm happy to try if it's what you recommend!

[Admin]

That seems reasonable, especially if the capacitors were rated at 10vdc, but as I said, I can't make that out from the diagram. The 5 volt regulators need at least 7 vdc to do their thing, so I would think that output of the rectifier would be a bit higher than that to allow for a margin of error.

What is the value of the resistor in series between the rectifier and CN12? Note that this resistor will drop the voltage when a load is placed on the supply and the measured voltage will be higher than the nominal 7 volts if there is no load. Did you take the measurements with a load present? If not, 11.5 volts may be correct here.

[tucsondave]

I looked at the schematic. The capacitors are indeed 10 volt. The resistor is 3.3 ohm 1 watt FP.
If the line voltage is correct at 100 volts then there is a problem.

td

[echan42]

11.5 volts may be correct here.

I felt a relief as I read those words, I did indeed take the measurement without a load present, what can I use to simulate one?

The resistor labeled R101 (looks like an 8 i know) is 3,3Ohm.

In my first post I linked the Service Manual's PDF, the relevant pages are 54 and 319. I don't want to make you download a PDF but referencing my blurry screenshots is definetly harder and more time consuming.

[Admin]

tucsondave makes a good point. What is the voltage you're feeding the transformer? Based on the value and wattage of the resistor, 11.5 volts would be too high regardless of the load.

[echan42]

If the line voltage is correct at 100 volts then there is a problem.

Thanks tucsondave good point, the supply line is most definetly 100V since the step-up transformer from 220 to 100 was my first suspect, measuring with load and no load gives a stable 100vAC.
So this brings me back full circle to the organ's transformer coil, I don't know what it should be outputting since the manual doesn't seem to mention, but indeed given the readings on CN12 and the repairs on the board I think it's safe to assume transformer is definetly outputting more voltage than when it left the factory and it either needs to be replaced.
Or as Admin suggests since I think there's no reliable way to know what the transformer used to output find a suitable power supply to replace the whole unit.

[tucsondave]

What is the voltage at D302? That's the only other unregulated supply. The capacitors there are rated at 35 volts so a higher voltage there would confirm a transformer problem.

td

[echan42]

25,0v which seems pretty much spot on. Could it be only one secondary coil is failing or do transformers generally fail in all coils?

[echan42]

I've taken readings from the bridge rectifier D301 9.5vAC in 11.5vDC out, following the diagram this is the first component right after the transformer coil.

[tucsondave]

The only way a transformer secondary can output a higher voltage is if the number of windings on the primary is lowered and that could happen with a short. A higher secondary voltage on one winding would require an increase in windings. Try connecting C12 to see if you get the 7 volts with the load. There may not be a problem except that Yamaha used capacitors with a too low voltage rating assuming the schematic is correct.

td

[terryp]

The +7L should be close to 7 VDC. It should not be even close to 10V with no load. Have you checked for any continuity between windings? I can't imagine that any windings would be wound on top of each other without insulation between them, but there might be a short between secondary 1-2 and another secondary. If you measure anything other than infinity between those pins and any others, the transformer is toast.

[echan42]

I wrote to many eBay sellers selling electone's el90 hoping to get a voltage reading and I almost got somewhere with one seller, but I've ultimately hit a brick wall.

Have you checked for any continuity between windings? I

I've measured between all secondaries and there's no continuity, can a transformer have a short between windings in the same coil?
It's so frustrating that all I need are 3 numbers to get this organ working again.

[terryp]

It seems like the biggest worry is the 10V rating of the electrolytics that appear to have 11.5V on them. I can't understand that. Are you sure your meter is accurate?

A short between turns of a single secondary would *lower* that voltage, as well as cause overheating. To check for such a short, plug the transformer in with nothing connected to the secondaries, and monitor its temperature for a few minutes. It should be barely warm to the touch after an hour or so.

If you don't get anywhere, I might be persuaded to open mine (120V primary) and check voltages, but it's such a hassle, as you know. If I didn't have to remove that dang dust shield...