Dead Onkyo M-504, help the inept please

[Raptor22]

Amp took a lighning hit and now stays in protection. Visual inspection shows 5 of the 8 LEDs no longer illuminate. Checked around in circuit with a DMM set to diode and found the following in regard to the LEDs:

All have near rail voltage with good drop across (this brings up next question below)

D409 - 412 check good at .5 vdc fwd but when checked in rev meter builds up like capacitance to 1 vdc and then opens (possible in circuit effect?). of this group only 411 illuminates.

D417 - 420 check good fwd and open in rev, 412 & 418 illuminate.

Regarding voltages, I assumed that the flag note call out on the schematic indicated potential to the associated rail. Everywhere I have check, I get near rail voltage except for Q441 and 442. These two are very near the schematic callouts.

Only other info I have is that the right channel idle current was 17 mV and was correctable via pot adjustment. Left channel idle current is 9 mV and the pot does not effect reading.

Any place for a layman to start determining fault?

M-504 main borad.pdf

[djk]

Take a two year program at your local community college. The second semester of your second year they will have you bring one piece in to fix for your grade, don't bring this piece.

After you graduate, get the schematic.

Check all four main supplies.

See if the amps have output before the protection relays.

Check the supplies for the protection board.

[Raptor22]

Thanks for your interest and help. College is a choice that has been discussed with the wife and she agrees (she supported me thru my aerospace engineering and business degrees) and older/vintage audio repair is something that could be fascinating to me following my second retirement. I want to ensure that I don't eroneously maticulate in an improper curriculum so please follow link and point me in the right direction http://www.chattcollege.com/ . Sorry this is my only choice of institutions at the moment. I AM serious! Really.

Now to the amp, if I can beg indulgence.

I have the service manual, including schematic, hence the attachment. I will certainly send the complete manual via .pdf arttachment to any one here on the board that would like a copy.

Both rails of both transformers are measured to be +/- 0.5 VDC within spec. The supplemental transformer for the meter board is good as well.

I do have a hard short between + rails in one polarization and 5kOhms with capacitance increase with opposite polarity. This is measured as meter red to B1- and black meter to B1+ producing the hard short. I state it this way because I am using a DMM and I have read that some DMM revesre the polarity in the resistance mode. Research tells me I could have a transistor or bias servo failure. Close?

Regarding amplifier output, are you asking for a voltage measurement at the point that the 1VDC fault is detected? My research has not led me to that circuit so that I can check it. It is not included on the one page I attached.

Guess I'll muddle along...

[djk]

(she supported me thru my aerospace engineering and business degrees)

You sound like my father, BSEE, MSEE, MBA, 23 years in industry, EE prof for both grads and undergrads, but can't fix the stereo.

"Regarding voltages, I assumed that the flag note call out on the schematic indicated potential to the associated rail."

The voltages are from the reference point to ground.

"The supplemental transformer for the meter board is good as well."

I think you mean the extra winding in the right channel power transformer? Do you have 12.6V on the emitter of Q702?

"D409 - 412 check good at .5 vdc fwd "

They're LEDs, they should measure about 1.8V fwd on the diode scale (amp off).

" 411 illuminates. 412 & 418 illuminate."

419 not being lit means something in the current mirror is probably blown (Q415, 417, 425).

"My research has not led me to that circuit so that I can check it."

It looks like the front-end is blown, as a bare minimum. I would check every transistor junction on the diode test, every diode.

This is going to be hard to fix. I could sell you a used M508 for less than I would charge you to fix this piece. Hope you have another amp to use in the meantime.

[Guest " "]

"This is going to be hard to fix. I could sell you a used M508 for less than I would charge you to fix this piece. Hope you have another amp to use in the meantime."

 

 

often the case

 

 

 

[Raptor22]

"This is going to be hard to fix. I could sell you a used M508 for less than I would charge you to fix this piece. Hope you have another amp to use in the meantime."

often the case

I'll certainly take you guy's input on this. I have had a quote from the only shop I know of in the Atlanta area for repair (norman electronics) for $65 for troubleshooting and ceiling of $179 before authorization is required for amp under 200 watts" plus email that my amp would be an average of $295. I don't know these folks and that pricing strcuture doesn't mean a lot (I understand why it's so broad). Perhaps the average quoted is realistic, perhaps not. If I can find a CLEAN 504 or 508 to make the finances make since, I would. Not gonna pay current epay prices. I paid $550 for a MINT in the box 508 locally about 2 months ago. FYI, I have sold off my 2 channel stuff for the most part, a sad day for sure as I have been collecting it thoughout my 23 years in the Navy from '73 on. Ahhh, our live's change...

Back to the subject, my current set up: Denon AVR4306 used as pre/pro to the Onkyos (1 x M-508 good, 1xM-504 good, 1xM-504 BAD, 1xM5060R good). Speakers are Chorus II mains, Academy center, Quartet rear surrounds with a set of RS-7s on the sides that I occasionally turn on for some Xbox 360 games (son's) and concert 5.1 stuff. My sub is an SVS PB12plus2 thru an SMS-1. My room is 14 x 26 x 8, I'm working on the room treatments and bass traps now. My personal opion of my speaker set up is that I'd like the mains to be a little warmer. I have a set of new caps for the crossovers bought from a forum member a year or so ago that I need to get in to hear if there is any difference, my web surfing tells me that they may well sound even brighter with the new ones.

All this to say that if there may be a better "package of amp(s)" that would be a monetary swap out, please speak up.