Onkyo TX SV727: Found bad transistors, what else?

[Zeppelin1007]

Re: Onkyo TX SV727: Found bad transistors, what else?

Jiroy, this is what the guy i know uses
http://www.apple.com/shop/product/HJ...duct-HJ102VC/A

China is good for some things, but electrical components...ehhh little iffy on. There is a massive industrial surplus here in Ohio that's never let me down when i need ancient parts that arent made anymore. I'll give them a shot too.

Update: got the 1k's soldered in. Did a quick continuity check, and was getting a short between B and E on the D2387. I figured it must be another shorted component in the circuit...i also touched up my solder job as it was a bit weak, and now I'm not getting the short. Now I'm scratching my head as to what caused it. Little leory to try powering it on unless i can be certain what my issue is. I just don't want to blow up more parts.

Petahall, i take it these are equivilants. Would it be wise to do both channels to the new ones you listed here?

Thanks guys.

[madan1]

Re: Onkyo TX SV727: Found bad transistors, what else?

Do the bad channel, listen to it, if you notice differences consider changing the tr on the other channel.
If you power the amp now ( with removed power tr ) you risk blowing another fuse due to other bad components which you have not found yet. I'd say better find them now than when you have the fresh set of transistors installed .
As I said before - the amp should powerup properly if you have removed the bad components. If it dosa not want to start, then you have more work to do.

[Zeppelin1007]

Re: Onkyo TX SV727: Found bad transistors, what else?

Success! She fired right up!

OK! Now the fun part: Transistors and resistors.

Thanks a ton guys!

[petehall347]

Re: Onkyo TX SV727: Found bad transistors, what else?

were the old outputs shorted ? they are darlingtons so wont test like a regular transistor. wont test shorted though if good .

[Zeppelin1007]

Re: Onkyo TX SV727: Found bad transistors, what else?

The old 2SB1558 and 2SD2387? yes. Both showed shorts from B to E in both directions both in and out of circuit.

[petehall347]

Re: Onkyo TX SV727: Found bad transistors, what else?

farnell suggested the subs . check data sheets to be sure of a close match .

[Zeppelin1007]

Re: Onkyo TX SV727: Found bad transistors, what else?

That's actually what I'm looking at petehall. Was trying to pinpoint what makes a transistor substitute compatible. Id obviously assume voltage and current ratings equal to and greater than the existing ones.

Question: I saw a guy on youtube replace some transistors with NTE based ones, that came with a glass/plastic plate. Whats the purpose of this? the ones i pulled off had little sticky pads on the back for the heatsink. How is this different than me putting some thermal paste behind the transistors before i bolt em on?

I was surprised she fired up! love the resistor test trick

[petehall347]

Re: Onkyo TX SV727: Found bad transistors, what else?

did you check dc offset ? i guess it wouldn't have powered up working anyway if not but maybe worth looking at in case .

[petehall347]

Re: Onkyo TX SV727: Found bad transistors, what else?

the plastic looking plates are actually insulating mica . this needs thermal paste on each side .only a very thin layer . its there to fill scratches in the surfaces .
do not use thermal paste intended for computers as some of it is conductive .
the output transistors must be electrically insulated from the heat sink .always test with your meter after fitting them for short from cases to heat sink .
i always check with my meter for any possible shorts after soldering anything back in the boards . it doesn't take as long as fixing a burned out wreck .

[Zeppelin1007]

Re: Onkyo TX SV727: Found bad transistors, what else?

Petehall, gotcha. Makes sense. Any kind of thermal paste you'd recommend? And what if the mica doesn't come with the transistors? Is there a generic supply somewhere i can grab more?

DC offset where?

[petehall347]

Re: Onkyo TX SV727: Found bad transistors, what else?

dc offset is where speaker output comes from . if speaker relay clicks on then at speaker terminals . if not right where the emitter resistors join together at the output transistors . they are the biggest resistors and low ohms .
mica is bought separately .just have search around to find a supplier .
any quality non conductive thermal paste will be fine . i seem to remember dow corning or something like that in your part of the world is good .

[rhomanski]

Re: Onkyo TX SV727: Found bad transistors, what else?

You can find the insulators at Mouser as well as the thermal grease.

http://www.mouser.com/Thermal-Manage...ulator&FS=True .

http://www.mouser.com/Tools-Supplies...grease&FS=True .

[jiroy]

Re: Onkyo TX SV727: Found bad transistors, what else?

were the old outputs shorted ? they are darlingtons so wont test like a regular transistor. wont test shorted though if good .

Definitely true . The best way to test a Darlington is to change it with a known good one . Its inside diode is really tricky .

[rievax_60]

Re: Onkyo TX SV727: Found bad transistors, what else?

The voltage difference between the Base pads should be measured to see if the idle current setting circuit is working properly.

[Zeppelin1007]

Re: Onkyo TX SV727: Found bad transistors, what else?

Ok guys. I found the transistors, mica sheets the right size..turns out i have some non conductive thermal paste.

Struggling to find the dual 0.22ohm 5w ceramic resistors, or, find them at a reputable dealer. Does Farnell have them as well?

Ive read i can just put 2 resistors in manually. Any specific kind that must be had?

[jiroy]

Re: Onkyo TX SV727: Found bad transistors, what else?

This page on Ebay include the Dual 0.22 Ohms , 5 W , Ceramic power resistors

http://www.ebay.com/sch/i.html?_nkw=0.22+ohm

[tibimakai]

Re: Onkyo TX SV727: Found bad transistors, what else?

I have purchased mine, from Ebay as well.

[Zeppelin1007]

Re: Onkyo TX SV727: Found bad transistors, what else?

Ok guys. Sorry ive been slow to respond. Works getting out of hand and I'll be out of town for the weekend.

So that means i ordered the transistors and mica so they'll arrive by the time i get back

Ok ok on eBay. Makes sense. Just didnt know if there was some secret stash online i didnt know about lol.

Anybody see a problem with me buying single resistors and pairing them up? I see plenty of 5W singles on ebay. Don't feel like waiting the month for the slow boat from china (nor do i trust it lol)

Thanks guys!

[madan1]

Re: Onkyo TX SV727: Found bad transistors, what else?

Yes, you can use 2 single resistors instead 1 double.

[Zeppelin1007]

Re: Onkyo TX SV727: Found bad transistors, what else?

Welp. I replaced the transistors, made a dual resistor, soldered it all in and she fired up!
There is a second relay on a delay that turns on after the thing powers up that clicks on.

Now, before I button it all up, should I be checking voltages/bias? If so, I hope its at the terminals and not on the board.

Thanks guys. This has been sitting on my "someday I'll learn how to fix this" pile. Easily 6 years.