Amp reconditioning

nh36000

Too many notes!!!
Gents;

After reading 'Groenhen's' post, I am prompted to write in as well. His first post and my first post, too.

I registered a couple days ago and have been reading a lot of recap messages since. I have a C-90, with a 'TV/Tuner' button, on the left end, making it a US market C-90A, I think, if I read some online information right. It's not a '91' but an upgraded '90'.

I now have the same issues that a lot of these units have, after 20 years. A scratchy 'balance' pot, the treble pot doesn't seem as bad as it was and playback that fades in and out once in a while.

I've also seen a page were some one reworked his M-90. I might think about doing something with the M-91 also. The F-91 seems to be just fine and I don't know if doing anything with that is needed or not.

I am a total newby at working on components but I can solder, listen to advice and follow instructions.

So, to begin with, I've taken the wood panels and top cover off and pulled the front panel, only to find that the pots are covered, their are cases on them. I'm not sure how to clean them, then. You know, how many times can the tabs be bent, to remove the covers, before they break? So, with that, I don't want to just dive into this project blindly. Any comments will be gladly listened to and heard. I have put the unit back together and it is working, like it did, before.

I am another one that needs to replace caps, relays and re-solder these things.

I'll keep reading posts and keep an eye open for replies. I'll watch Groenhen's post as well. He started a thread today, too.

Thanks ahead of time for any help any one can offer.

Lu

New Berlin, Wi.
 
All;

I have read a few more threads and ran across Arkey's post about De-oxit. I wanted to write in here and ask about it but, after finding the thread, I now, don't have to. I'm sure that I will go out and try to find it today. Would the 'Shack' stock De-oxit?

The singer in one of the night-club bands I've been in, would put some time in at his Dad's TV repair shop, just helping out. They would buy from a place called Marsh Electronics, for components and equipment. That place has been in business since the early '60's, maybe longer than that. If RS doesn't sell it, I'll go over to Marsh. I'll give everything, here, a good cleaning and see how things go. I'll look for leaded solder and try to find a solder vac today, as well.

One more thing here I'd like to ask. I think I remember reading that some of these blackface Pioneers would have gas filled relays in them. I haven't any plans now to do anything with the relays, now, though it looks like a recap might be in order. Please, let me know, would I need to do anything with the relays, down the road? Would a leak test be needed? How is bias set? What needs to be heat sunk when soldered? These are some of the things I would like some help with. I haven't got a scope but I do have good circuit testers.

More later!

Lu
 
Hi Lu and welcome! I'm newish here myself, but had the same issue w/the balance pot on my SX-750. After some minor disassembly and the use of some small diameter shrink tubing as a remote delivery conduit, De-oxit/Faderlube fixed it right up.

I got my DeOxit products at the local Guitar Center store in case that helps.

Ron
 
Ron;

Hi!, and welcome to you, too. I think I'll give RS a phone call first before I head over there. There is a Guitar Center not too far from here but an Interstate Music (ex-Casio's) store not even 1/2 of a mile from here. BTW: I bought my first electric guitar, a Rickenbacker 345, as they were called then, and a blonde Fender Bandmaster, at the original Casio's store, in 1967.
Maybe Interstate has that stuff there. I'll give them a try.

I just want to get these things cleaned up first, to find out what shakes. Decide what to do after that.

Thanks for writing back, it's good to read your comments. I have a good idea that cleaning won't solve everything here. The amp, pre-amp and receiver are all 20+ years old and most likely, need a rebuilding. I have an SX-828 here too, the volume pot bearings are shot. Frozen at 3 1/2. Ebay auctions offer 500K two deck Pioneer pots for $25. I just might buy one of those, sometime. I did like the way that amp sounded, haven't used it in a while, though. Purchased it in 1974.

So much for all that, I'm off to the stores.

Lu
 
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Ron;

Hi!, and welcome to you, too. I think I'll give RS a phone call first before I head over there. There is a Guitar Center not too far from here but an Interstate Music (ex-Casio's) store not even 1/2 of a mile from here. BTW: I bought my first electric guitar, a Rickenbacker 345, as they were called then, and a blonde Fender Bandmaster, at the original Casio's store, in 1967.
Maybe Interstate has that stuff there. I'll give them a try.

I just want to get these things cleaned up first, to find out what shakes. Decide what to do after that.

Thanks for writing back, it's good to read your comments. I have a good idea that cleaning won't solve everything here. The amp, pre-amp and receiver are all 20+ years old and most likely, need a rebuilding. I have an SX-828 here too, the volume pot bearings are shot. Frozen at 3 1/2. Ebay auctions offer 500K two deck Pioneer pots for $25. I just might buy one of those, sometime. I did like the way that amp sounded, haven't used it in a while, though. Purchased it in 1974.

Well, I'm off to the stores.

Lu
 
Any one, please:

The two messages ahead of this one is a mistake of mine. I thought I'd edit the post, before uploading, but didn't see the duplicate until I reopened the site to read the results. I am not sure how that happened, exactly, but I will make efforts to have one of them removed. And, my not being a subscriber, I'm not sure I could do that myself. Maybe administration can help? We'll see.

I've recently looked up specs. on the subject of eutectic solder and I am wondering if Sn63%-37%Pb is the type to use here. There are solders out there that contain bismuth and/or silver as well. Might that be something to use or, would the 63-37 work well enough? A type 3 flux was also listed as the type to use with this kind of solder.

I'm having a heck of a time finding a solder sucker in this town. OK Industries DP-100 looks good, expensive, but I could mail order one. Amazon has them too, and for under $5, plus shipping.

May I ask? As I've been calling places, driving to places and reading threads for leads, in the last two days, I did get ahold of De-oxit cleaner and Gold, from Guitar Center, finally, but that's all. This all seems to be some pretty long haired material. Where do you guys buy these things from? No one seems to have these kind of things around here. I though Marsh would, but they don't sell over the counter now, and haven't for over 25 years. You can tell I haven't been there in a while.

Help!

Looking forward to reading your comments;

Lu
 
www.partsexpress.com sells CAIG Products, solder suckers, etc. Sometimes on sale too.

You should be able to delete one of the posts. Hit EDIT, then on the new page look for a delete post section.

Regular 40-60 Acid Core solder is good enough. .022" diam is good for the small stuff. If you use the 37-63 stuff you need to completely desolder the joint. Don't use the lead free junk.
 
Larry;

I'm still online here. Thanks much for the information. I really am having a tough time finding some of these things.

It's getting close to dinner time and I need to put something together to eat now. I'll give an edit a try tonight.

Thanks again!

Lu
 
All;

I spent around an hour tapping out a detailed massage about what I'm doing with the C-90 pre-amp and, through log-in issues, ended up loosing the whole massage.

So, this is my second attempt. And, to make a longer story short.

I have opened up the bottom of the unit. It looked easier to get at the front pots from the bottom. It really is but here is what I'd like to say.

Looking at the top board the first time I opened it up, the unit looked mint. The bottom board, though, is burned around the black painted wood block to the right hand side of the PCB. There is a yellowing spot towards the back of the board as well. Not bad but discolored.

Recalling the first message, I bought these three units better than 10 years ago and listened happily to them since. I don't know if they were rebuilt before I bought them , who knows. I made an attempt to lift the bottom board with it still attached to the back panel, I turned the four screws back in and went upstairs to post. I don't know what the component side looks like, I haven't pulled the board yet.

Would anybody tell me what's 'cooking' that board and how I might repair it? I always thought that the power amp was a bit of a space heater but I never noticed the receiver or pre-amp getting too warm. I do not know how diagnose issues like that myself so I'll ask for help. Maybe the heavier hitters here can let me know what to do now. The only symptoms I see are the balance pot and the treble pot. I can turn balance to the left channel and hear nothing. Center it, and with a little wiggling, the both channels come back. The system works but, recently, either channel will fade in and out. Not too bad but they do.

I did De-oxit the front pots this mourning but haven't used the 'Gold' on them yet.

I just thought it disappointing to see the bottom board burned like that.
It all looked so good from the top.

I'll get online again later and, hopefully, read your comments,

Lu
 
Gents;

I'm bringing this one up to the front page again.

Two weeks ago, I had started to clean up the C-90 with the use of De-oxit. I must say that the cleaner and Gold treatment did wonders for the pre-amp. No more turning the balance to left cannel and hearing nothing. I had flipped the unit over and got at the audio pots from the bottom, it was easier to get to them that way. I worked over the RCAs in the back and cleaned up the connectors to the front panel as well.

Two Thursdays ago, I put the pre-amp back together to preview a tape collection I bought. The tapes sound fine and I even ran the amp all afternoon one Sunday. No scratchy pots and no channels fading in and out.

Now, to any newcomer here, De-oxit is really the first thing you should use in fixing up an amp. Fantastic stuff and I think it would cure a lot of, what you might think, are amp problems. De-oxit is a bit expensive but well worth it. It's not too easy to find but don't go to RS for it, too high priced there. I think it was Larry that said that his was purchased at Guitar Center and that is where I found mine, too. (They keep it in stock there.) Many thanks for that bit of information.

Well, previewing tapes is finished and I will open up the C-90 and continue to clean up in there. There are other connectors I'd like to get at.

I still want to address the burned solder mask of the bottom board. Mosfet transistors and heat sinks, perhaps?

More later,

Lu.
 
Hennessy;

Yeah! The first post has a photo, at the right hand side, that looks nearly exactly like the board in mine. Including the spot towards the back of the board.

I dialed up here to have a quick look but I'm going to watch the ball game now and I'll read the thread first thing tomorrow morning.

Thank you, much!

Lu.
 
Gents;

As much as I know of electronics, does the board voltage change in a 220/240v input compared to a 110/120v input of the US units? I just had a good look at the C-90 service manual in the database collection. The manual there is for the West German market.

If you asked me, for instance, I would think that board voltage is board voltage no matter how much wall voltage you need to use. Am I correct? I am thinking ahead of myself here, I'm not done cleaning things, but am planning to refer to the manual in the future. I am also researching the testing of components on the boards in there.

BTW; I did read the thread Hennessy brought to my attention and 'WHEW', I think I've got a lot to try and learn.

I'm still trying to know which part number the bottom board is. Maybe it's silk screened on the board itself. I'll open it up again soon to have a look.

More later,

Lu.
 
Gents;

One more quick thing here.

I know how elementary it might be but I need to ask. The J400 series of connectors on the top board seem very tough to pull. Is there any trick to disconnecting those? I just want to ask before I manage to break something. Also, how do you get those wires loose that are wrapped around a post soldered on to the board? Can they be turned the other way to loosen them up and then pull them off?

Thanks ahead of time,

Lu
 
You will be buying items from Mouser, Digikey, and Parts Express.

Parts Express has the Deoxit if you don't find it locally. They also have the solder sucker. I personally like solder wick for removing solder rather than a solder sucker, just a personal preference. Use what you like.

Mouser and Digikey will have most of the electronic parts: capacitors, resistors, diodes, transistors, relays, etc.

RS doesn't have much.

Use Rosin core solder. 60/40 is fine. Do not use "acid core" solder. Neu's Hardware on Q and 41/45 has a good selection of solder.

There are a lot of helpful and knowledgeable on this forum. If you have questions, just ask.
 
Amp recondtioning

Gang;

Good news!

As I said in post #14, I need some advice in disconnecting things in order to pull the top board, i.e., J400 series connectors and wire wraps.

After doing a search of this forum, I found a thread by PioneerElite were Hennessy answered, This all back in 2009. PE asked questions about connectors and Hennessy said that, as old as these units are getting, the thing he does is just de-solder the pins and pull them from the board. You may stand a good chance of breaking the coils off, if you try to de-solder the wire coils, the solder may be brittle, things like that. Or cut off the coils, trim some insulation back and hard wire them back in the board when reassembling the unit.... Great advice to my thinking and I did de-solder the wire coils earlier this morning. I can solder them back in when I put the unit back together.

I'm still having a rough time trying to get the J connectors off. Here's a list: J401, J401L, J401R, J402, J402L and J402R.

Please, if anyone has some experience in working on these, let me know how to disconnect those. There are as many as 6 pins on one of them and I don't believe I could de-solder them from the board. I'm stumped but they come off somehow. Maybe they are latched or something, I've chipped corners, all ready, trying to pry them up.

Please help,

Later.

Lu
 
Pictures? Close ups of the connectors.

Sometimes, while they LOOK like connectors, they really are just soldered in wires.

Also never unwrap the wires from the square post - carefully unsolder the post from the board. Wire wrap is INTENDED to nick the wire at the corners, and that weakens the wire to flexing, thus wires break off short, a major pita. Technically on a wrap there should be a strain relief wrap at the wire, where it is mechanically tight, but not tight enough to nick the wire.
 
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Mark;

Unlike the last message, the bad news, here, is that I don't have a digital camera at my disposal. I have been looking through threads, for photos, others have uploaded, trying to find connectors like that. This C-90 being of the reference series, I'm not finding similar connectors in any photos of silver face amps.

I'll keep looking though.

Later;

Lu.
 
Mark and all;


I just spent some time online and found some photos of C-90 inerds (if you will). Two of the pics I will load up here.

The first pic is really the top board of a C-91. I can see things are different here other than board color. What's circled in blue are the 'connectors' I'm writing about. I picked this pic for the top down view and the side view. What's circled in red is the board part number. Hard to read but I think it reads, AWZ 2340. There is a wire bridge under that, which more than likely is, the real part number. The top board of mine is the same way. AWZ 1042 is listed and below that, 1044 under a wire bridge.

The second pic is the biggest photo I could find of these connectors, again, circled in blue. Thinking of the idea, you might be right, these things might be wire terminals that could just be de- soldered.

These 'connectors' are the last things to unplug before the board is free. I really want to get a look at the three transistors on the bottom board with the top one off.

More later and hope to hear from you,

Lu.
 

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One thing I know is that the top board can be removed very fast and easy. C-90 and C-91. Did both. Not once. Only de-soldering points are those wire wrapped.
I do not remember any press-in gray disconnects there. There are none. Only white pull-off. Those come easy if helped with a tool i.e. thin screwdriver at the clip side. Anyway, if OP is at unease, you can just de-solder the offending connector and call it a day.
Have in mind that on this machine there are no un-disconectable harnesses. Means that if on one board the connector is soldered in, and harness goes to another board, at that second board the harness termination will be disconectable. Not applicable to wire wraps, though.
 
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