Amp reconditioning

All;

Well: I've got the top board off to look at the bottom board. I unsoldered those pins from the board. And I don't know why a plug and socket wasn't used there like all over the rest of it. Long story short, done. I'll worry about putting back together, later.

There are three transistors and heat sinks labeled D836A. The screws and insulating grease look good. The glue between the sinks to board is no good anymore and the all three can be wiggled around. The board is burned there on the solder side and so is the top board above the transistors there. I hadn't known it before but those components are getting hot. the three trannys are listed on the board as, Q706, Q710 and Q712. The board is labeled E and C there. I guess that says they are Bi-polars then, yes?

I mentioned that I would reference the service manual in the database but after looking at it better, part numbers are not the same, caps, transistors and connectors are all numbered in different '100's'. I'm not going to try to refer to that manual to do anything with this one.

I've looked in Ebay for an SM but have not seen anything yet. I'd like to find something on paper, hard copy reprint or something. Pioneer want's near $35 for them. Maybe there is something some where that's cheaper. Hope so.


I'm now going back to studying components and how to test them. (Actually, part of the reason why I'm enjoying this project.)

More, later;

Lu.

Gents;

Well, in between studying components and waiting on an order for soldering supplies to arrive, I started to re-float solder. And I'm glad I did.

Toward the back of the board are two places where the solder mask is gone, over a thin trace. In one of those spots, the copper trace has curled up. I used an Exacto to push the trace back down but it doesn't look like a good connection. I've seen lab techs put a bit of solder across those and I think I will do the same. Maybe a little clear enamel on it after soldering. The trace break connects two different wire bridges. This all on the top board.

I've read about a sloppy glue job, in other posts here, and my unit is no different. I fount two caps, on the bottom board, glued together and then the glue dripped down the larger one and puddled up under the cap. It's all over a wire bridge, two resistors and what looks like a diode. Component leads are corroding, too. A mess indeed. I pulled the caps to test them and they seem to be OK.

Ummmm, though I don't know for sure, I'm hoping nothing needs to be heat sunk, re-floating solder on either of those boards.

Some of the latest;

Over 600 views here, all ready, somebody's reading this thread. WOW!

Lu.

Help needed

All;

Does anybody here have a good way to replace solder pads on a PCB. I'm trying to fix up under three transistors on the bottom board. It seems that the solder pads come up with the transistors and sinks when moved around. So, I can't be sure that the transistor pins are connected to the board at all. They are loose. Might that be why the board is dis-colored there? I know the bottom board is there for video, but if it's causing problems, I'd like to fix it up.
Caps, resistors, whatever.

Lu.

There are ways.
It is called PCB eyelet. They come in different sizes, you have to choose carefully.
Example: Mouser Part 534-24.
Then hard-wire it by soldering, or if the trace is burned, with thin tin plated copper wire, i.e. those you cut from polystyrene capacitors.

reply to Hennessy

Thank you for writing back. And I will look that PN up. I've watched YouTube vids on the subject and have an idea about how that goes. I'm just a little worried about the three D836A transistors on the bottom board. Maybe I don't need to be, I don't know.

One more thing!

I just got off the phone with Pioneer, looking for service manuals, and was told that Pioneer no longer has replacement parts or service manuals for sale, from them. This really leaves me in the lurch.

So, I'll make a plea, here. If anyone has service manuals for C-90's, built for the US market, F-91's, same, and M-91' same, that could be sold out right, to me, or be willing to make copies for me, I'd be perfectly happy to pay for those copies. It doesn't look like they will be easy to find, any more. Not having service manuals, to look at, has slowed me down.

I plan to write again about ordering replacement parts for the C-90 but not just this instant.


Later,

Lu.

Help needed

All; (C-90)

I have fixed up the bottom board working on the three transistors and their heat sinks, as best I could. The board still looks like it could use a whole new board. It's in pretty rough shape. 'Always has been.

I put everything back together, top and bottom covers off, plugged in the power cord and pressed the 'on' button. Nothing happened. No lights on anywhere. I pushed the stand by switch a couple times and still, no lights. I pressed some front panel audio buttons and same thing.

I did a continuity test on the power cord and it seem to be fine. I spent some time looking for fuses but did not find any. If fuses are there.

Might this be a relay issue? While working on the unit, I didn't do anything with the 120v side, at all. Checked the cord I plugged the unit into and plugged the unit into a wall outlet as well. Still, no power 'ON'.

Any suggestions, please.

Stumped;

Lu.

Yea, you probably screwed up something there... Not knowing what, it is hard to advise.
Anyway, it needs to be determined what is preventing the start circuit from operating. It can be a myriad of things. I do not know what did you replace with what even.

paper reproduction manuals, EXCELLENT QUALITY: STEREOMANUALS.COM

checked site, they are listed

disclosure: happy (multiple) customer...

Reply

Hennessy and Mark;

OK, here's all I did.

I gave the pots, jacks and connectors a De-oxit treatment. I pulled bottom and top boards to refloat solder. I have also repaired traces and solder pads on the bottom board around three transistors which dis-colored the PCB.

Everything was put back together and connectors plugged in. I plugged the pre-amp in to power and got nothing, this was Saturday. (I believe Mr. H is right, I must have screwed something up, in there.) I would also like to add the fact that no power is getting to the three 120v outlets in back either. I tried to light up the tuner from back there and still, nothing there.

I don't know, it's just dead in the water.

I got a reading of 0.05 on the 200 ohm scale bridging the ON/OFF switch posts, switch on and standby off. Not sure what to test next.

I also looked up SM's and I will send them an order soon. Thanks to Mark as well!

Yeah, so, that's it, I haven't replaced any components yet, everything's still original.

All for now.

Lu

One of the three power outlets is powered from the switch, therefore should work. The other two are from relay.
One of those SD836 darlingtons powers the on/off circuit with 12V. Considering there are no other faults, start checking that circuit. Beginning with 4.7 ohm resistor. Should get 19V at collector with power switch on.
On the other hand, it is a good practice to check for proper voltages at transistor BCE points when some work has been done around.
Get a C-91 SM in pdf from the web for a start, there are no C-90 U.S. model manuals posted for free as far as I know. C-91 is very similar.

Quickly, here.

I have been reading web pages and watching 'vids' about board repair for a few days, now. I think the condition of the board might be part of it too.

While still working, retired now, I used to make board art. You know, trace drawings, solder masks, silk screen drawings and drill guides. I've looked over the board pretty well and a trace drawing doesn't look too complicated. I've drawn worse! Still studying the idea but cutting another board 'might' be a viable option. Now if the service manuals have a good drawing of the board traces, I could work with that.

And yes, the C-90(BK) in the database doesn't have a video board in it.

Hogdaddy's thread, in 2012, told me a lot. I would like to start thinking about replacement parts now. Caps and relays, should I test transistors on the AF board? Should all the caps be replaced or just some?

More later, waiting for supplies.

Lu.

The unit has to be fixed first, and be in working order. Then general re-caping, and other replacements can be performed later to ensure it's reliability and longevity.

Reply to Mr. H

I've got some repair stuff on the way and I will fix up traces and solder pads. I'll lay off finding replacement components then and get the board working. Typical stuff where the board is dis-colored, the copper doesn't stay put, anymore.
Lu.

Latest, and a shout for help.

All;

Just this past Tuesday, I received an additional C-90, bought on an Ebay auction. You may have seen it on auction, it's the one without the wood panel screws. And that's a story in itself, too.

The seller out in California was fantastic to deal with, many posts between us about it and more than happy to do what he can to get it to you. I sent a $100 deposit and the rest a week later.

He said it was in mint condition and it is. No burned video board and it looks like some of the components have been changed out. The bottom board's solder side can be seen through the bottom cover and there is fresh solder at those three big transistors and their heat sinks. 'Haven't opened it up to see if relays and caps have been replaced. They just might be, maybe I will open it up to have a look. The seller in Ca. is new to Ebay but he sells just EXACTLY what he describes in the auctions. I know, I have one. And if he describes it as a piece of junk, it's a piece of junk. If he says it's mint, It's mint.

In repairing the other board, I'm having trouble finding trace epoxy, without spending $700 for a 'fixit' kit. I know you need a certain type of glue, something that can stand up to solder temperatures. With the experts out there, I feel kind of funny asking but could somebody point out the right kind of glue for that, please? :sigh:

Thanks ahead of time as I don't have the other board fixed up yet.

I'll write back again, this thread nearly fell off the last page, here.

Lu.

In need of help.

Well, the second C-90 I have just quite starting up. That makes two.

I went to turn the amp on and the stand by light was flickering, not like it was on stand by but like there was a loose connection in there somewhere. Then, finally, not lighting up at all.

I'd like to get it up and running again after seeing the C-91 service manual in the data base, here in AK.

Relay RY405 is listed as a function on/off and I'm wondering if that could be the cause. I'd replace relays if it is.

It's a fact that both fizzled out within a year of each other.

I would be glad to answer any questions asked as best I can.

Please help.

Lu.

Latest news

Seeing message #35, I meant to say 'quit starting up'.

I just received fourteen relays, ordered from Mouser, in the mail today. I am going to finish pulling the top board and trade out the old relays for the fresh ones. Hopefully, it will get the pre-amp working. I'm replacing G2VN-234C-PA2-12VDC's with G5V-2-H1-12VDC's.
I saw that part number in another thread from someone, fixing up their C-90 as well. The first pre, I have, has 237C's in it.

And yeah, I've read about sliding strips of paper under the relay leaves to clean them but with that, you would still have decades old relays in there. Many have said, just replace them and play the system for another 20, trouble free years, then. Good idea. And that's what I'll do.

Here's hoping this will do it.

Lu.

Well, I just got done changing out relays, this morning, reassembled the C-90 and plugged it in. I pushed the power switch and it didn't start up. No lights anywhere either.

I even plugged it into the power amp and sourced the radio, I thought that, maybe, just the lights didn't work. That wasn't it either. Is something is shorted in there? I don't know.

Stumped! What should I look over now?

Anyone with any ideas?

Lu.

Amp does not power up

Gents;

I just plugged a tape deck into the AC 'outs' in the back of the C-90, power switch, OFF. With a deck 'ON', I tried all three, I pushed the pre-amp switch 'ON' and the deck turned on using the 500 W. Max outlet but not 'ON' with the other two.

Hennessy said in post #30 that I do that and I finally did. I now have 26+ connectors unplugged so I haven't tested for the 19V output of the D836A's at Q706, 710 or 712. If that's something very needed, I'll reassemble it do that too. I just haven't done that yet.

I pulled Q710 and tested it with an MM. I got some readable number at the 20K range in Ohms. The display read about 157.(something), then drops to 9.4 and then to 0.0, all in about one second, red lead to base and black to collector. Black to base and red to collector, same thing in negative numbers. A '1' is displayed all other ways.

I also tested it with the meter set to HFE and got zeros no matter how I connected the meter, all six ways. D836's are NPN bi-polar 'planers' I don't know what planer means but in an AF board they are being used as switches so, from what I've read, they would be working in saturation. On or off with enough voltage applied to the base. (I've been reading up on some of this stuff and have learned a few things, not enough to diagnose though; naturally.)

Now, with those readings on the MM, is that transistor working right? Something in the amp is not letting the amp turn on, and I don't know what. It made sense to look at the switch circuit first, as Hennessy said.

Another odd thing here is that the input jacks on my Realistic 10 band equalizer haven't been working since the pre-amp quit turning on. I had it plugged into the C-90's adapter jacks in back. Maybe that says something.

All the latest, here.


Lu.

Why won't the amp turn on?

Hailing Hennessy, please;

Since you were the one that wrote to tell me to check it, I want to say that I finally did.

The 836A near the 4.7 ohm resistor is Q712, I reassembled the amp, plugged it in and grabbed the MM. I believe this is what you wanted me to have a look at. I'm not sure though.

I tested the trany all six ways and got a reading of .44+/- between collector/emitter, emitter/collector, MM set for 20V range. Nothing anywhere else.

I did not find 19V there. Did I check that the way you asked me to? It's quite possible I didn't do that right.

By all means, write back to let me know.

All for now.

Lu.

2SD836A is a Darlington transistor with built in resistor and diode. Testing it with a MM is quite problematic or even impossible. BTW, substitute is a TIP110-112. 19V has to be measured at one of R904 and R912 4.7Ohm resistors legs. Q710, Q712 ~ 12V at emitter.
I would be more concerned about 19V power to the ICs. Means checking Q702 and Q704 for +/- 19V at emitter, R913 and 914 resistors for open.