Any Yamaha M-50 Experts Out There???

I did the first test for control circuit board 1 which requires a jumper on TP1 jumped over to J605 which is directly below it on the board. Readings are taken from GY and VI for AC voltage off of the capacitor board. I get the second type of result described in the manual where the observed AC voltage is proportional to the line AC voltage. At 123VAC line the reading at the test point(s) is .33VAC and it should be about 5.5VAC

So the manual says I have a shorted SCR, Triac or Control IC.

Here's all of those parts...

SCR601 .3A SFOR3G42 >> ???
SCR602 .5A SMOR5G42 >> ???
SCR603 16A AC16DGM-L >> ???
TR601 2SA949 >> KSA1220
TR602 2SA970 >> KSA992
TR603 2SA970 >> KSA992
TR604 2SC1815 >> KSC1815
TR605 2SC2240 >> KSC1845

TR606 TLP508 Photo Coupler which looks to be transistor and diode in a combined package...I checked the pin outs with my meter and it looks to be OK with a basic diode and transistor test.

IC601 IG04080 which I assume can only be replaced with an exact like item?

Any thoughts on which one(s)? Or, what I can use for the parts I haven't identified a sub for?
 
I figured that...I want to troubleshoot that part to rule it in or out as being the problem. Any thoughts on that?

Also, what are all the yamaha models that use that IC in case I need to find a replacement?
 
There is no much information about IG04080. I found this schema, perhaps it could be done with discrete components.
 

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I'd just end up replacing it with one from a donor unit if that ended up being the issue...I'm wanting to prove or disprove that it actually is the issue...the test procedure explains that it could be several things...the transistors are a much easier replacement. I need to understand how to track down the blown part first.
 
I finally got a control board parts unit so I can troubleshoot my m-50 control board to see if I can narrow down the power issue.

I currently have the control board 1&2 wired into the power switch and everything else is disconnected...no transformer, no cap circuit board or anything else. I also have the transformer removed and all the primaries and secondaries Ω out. When I hook up the transformer alone to the control board the voltage supplies to the transformer drop down to a couple volts but when no transformer is connected they read 125vac.

Seems that the transformer is OK so I need to troubleshoot the control board(s).

Any help?
 
I finally got a control board parts unit so I can troubleshoot my m-50 control board to see if I can narrow down the power issue.

I currently have the control board 1&2 wired into the power switch and everything else is disconnected...no transformer, no cap circuit board or anything else. I also have the transformer removed and all the primaries and secondaries Ω out. When I hook up the transformer alone to the control board the voltage supplies to the transformer drop down to a couple volts but when no transformer is connected they read 125vac.

Seems that the transformer is OK so I need to troubleshoot the control board(s).

Any help?
 

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Turns out the transformer has a short in it between the primaries and secondaries...when I attempted to power it up by itself without a load it blew the circuit breaker instantly. Very slight Ω reading between the primaries and secondaries...barely reading megaohms...anyways, any is bad...should be fully isolated.

SO...does anybody have a spare M-50 power transformer sitting around??
 
Turns out the transformer has a short in it between the primaries and secondaries...when I attempted to power it up by itself without a load it blew the circuit breaker instantly. Very slight Ω reading between the primaries and secondaries...barely reading megaohms...anyways, any is bad...should be fully isolated.

SO...does anybody have a spare M-50 power transformer sitting around??

Hey so I know its been a long time since this post. I'm working on trying yo fix a M-50 and I'm reading a lot of similar results as you so know i'm wondering about testing the transformer. Do you remember how you tested it? I am getting a short between 'TT' and 'T1' on the power control board but I know idea if thats normal or not.
 
Looks like we are both chasing the same squirrel! :rolleyes:

SCR601 = SFOR3G42 = 576-S4X8ES? or Q4008L4? The pinout confuses me greatly.
SCR602 = SMOR5G42 = P0109DA-5AL3? or NTE5655?
SCR603 = AC16DGM-L = Q6015L5? The pinout confuses me greatly.

Very slight Ω reading between the primaries and secondaries...barely reading megaohms...anyways, any is bad...should be fully isolated. Do you still hold to the statement that any resistance is bad?
 
Were you able to determine the issue:?

I currently have the control board 1&2 wired into the power switch and everything else is disconnected...no transformer, no cap circuit board or anything else. I also have the transformer removed and all the primaries and secondaries Ω out. When I hook up the transformer alone to the control board the voltage supplies to the transformer drop down to a couple volts but when no transformer is connected they read 125vac
 
Looks like we are both chasing the same squirrel! :rolleyes:

SCR601 = SFOR3G42 = 576-S4X8ES? or Q4008L4? The pinout confuses me greatly.
SCR602 = SMOR5G42 = P0109DA-5AL3? or NTE5655?
SCR603 = AC16DGM-L = Q6015L5? The pinout confuses me greatly.

Very slight Ω reading between the primaries and secondaries...barely reading megaohms...anyways, any is bad...should be fully isolated. Do you still hold to the statement that any resistance is bad?


Hey not sure if you were trying to reply to me.

https://audiokarma.org/forums/index.php?threads/yamaha-m-50-stuck-in-power-protect.881664/

I got mine fixed finally and it was basically just poor solder all over the driver and pre driver board.
 
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