Quote from: J M Fahey on January 31, 2009, 11:18:05 PM
Beatiful piece of equipment. Is it a single 240W power amp or two 120 W units? In any case, you´ll find on the net the schematic of a Traynor 100 or 120 W power amplifier, with two MJ802 devices; it should help you repair the one you have, being basically the same.If you can´t, I´ll search it into my poorly organized files .

Thanks.  I have not yet found a 100w or 120w amp schematic, but the 200w that I did find has different devices altogether than the YVM-10L.  I understand from the Yorkville site and history write-up (http://yorkville.com/downloads/other/yorkvillehistory.pdf) that the amp is the "YPM-250".

The amp is just a heavy single box inside the mixer compartment with two parallel 1/4" speaker outputs labeled "250W 4 ohm".  The transformer is heavy-duty!

Here's a picture after I opened it up.  The top of the amp case has the 120v fan on the back, and I moved it out of the way (behind the reverb unit mounted on the bottom).

I will continue the search now that I know that the YPM-250 is the schematic I want. 

Phil

Quote from: syndromet on January 29, 2009, 05:01:34 AM
I say you replace one transistor. If it works, you have 15$ to spend of something fun. If not, you have to replace the 3 others anyway. Recapping is always a good idea on old stuff, especially the electrolytics. For cleaning pots you could try compressed air. It has done wonders for me.

Thanks for the reply. I pulled all 4 out and tested the base-emitter junction voltage drops.  2 were almost identical (0.524v), but one was a little higher (I think about 0.65v). 

I was thinking about being cheap and only replacing one, but then decided to save up and replace all4.  I was kidding about whether to replace them all (as my non-technical wife suggested).

Compressed air is a possibility, but I was eyeing some chemicals like contact cleaner and hoping there was something better.  On Google, I found "Slider Libe" or something like that. Probably better than electrical contact cleaner.

Do old electrolytic caps loose "capacity" as they age?  Or are they subject to breaking down/leaking under voltage?

What about the little electrolytic caps on the printed circuit boards?

Thanks!

Here are the remainder of the pages.

Additional photos of other pages from the envelope.

Yesterday I picked up a Traynor YVM-10L mixer with 240 watt internal power amp. It's a 10 channel mixer made by Traynor in 1976.  I was told the power amp doesn't work, but the mixer is dirty but OK. Yep, that's what I found.

As I opened it up, an envelope fell out which contained 10 pages of hand-drawn schematics for the mixer section.  Here are some of the photos I took of those pages.  The others in subsequent posts. (Had to reduce the size to get them to fit.)

I wish I had the schematics for the power amp though, but searches on Google proved fruitless.  I also couldn't find anything like these anywhere either, and want to make them available

Output uses 4 TO-3 MJ802 power transistors, and while testing, I found that 1 is shorted E-C.  I hope that's all that's wrong.  My wife thinks I should replace all 4, but for crying out loud, they are $4.60 each! Well, she said I could if I wait until after Feb 1 (finances being what they are).

So, is my wife right? Is it worthwhile replacing all 4?

Also, should I replace the power supply caps?  I say one guy comment that he was "recapping" his PS.

Oh, by the way, what's the best way to clean the zillion dirty pots on the mixer?

Thanks for any advice.  Phil

Oops, typo: YVM-10L, not YVN-10L as originally posted...sorry.

I did receive the original as a JPG.  It didn't seem very big when I got it, but I was thrilled to get it!

Here is the file as received.  I cannot see any difference in the clarity however.  Hopefully, you can see what you need however. 

Phil

While waiting for parts, I looked closer at the power-amp board for issues.  I metered the diodes and found nothing unusual, but found a burnt/broken trace on the board. 

The circuit board trace from the +Hi supply to the power-amp chip was burnt open.  I considered options and decided to add a wire in parallel from one component lead to another component lead providing the feed needed.  Here is the pic I posted earlier blown up and the broken trace circled. 

If curious, I can post pics and more detail of my "repair".  I am tempted to also stabilize my added wire with hot glue to avoid future breakage from flopping and flexing.  After I soldered it on, I wished I had shortened it though; it's probably about 2" longer than it could have been.

By the way, Teemu, thanks for your analysis of the circuit.  I don't work in the industry and got my Associate Degree in Electronics Technology in 1985.  Lots of changes in electronics since then, and I do not know what a 'class-G -type "high efficiency" circuit with switched supply rails' output circuit is.  But it sounds like it would be good to have to get the power rating claimed.

Here is an another attempt at attaching the photos I tried to get last post.

One is the bad power-amp chip cooked and partially exploded, and the other is the board I got it from.  Maybe I'll try the big pic too showing the whole project.

Now, I'm in trouble-shooting and repair.  I found the 3 amp primary fuse blown. 

I replaced the fuse, unplugged the power amp board, then turned it on. 

I checked the AC voltage from the transformer (OK), then the DC voltages referenced to ground.  First the + and - "Lo" sides (plus and minus 17vdc) (OK), then the + and - "Hi" sides (plus and minus 43vdc) (OK).  Then when I checked the + and - 16 vdc for the preamp chips, I got +16 and -3.  Bad... (On the negative side, 40 vdc was being dropped through R52, a 390 ohm 7 watt resistor).

I unsoldered and removed D11 (one of the 16v zehner diodes) then bench tested it.  I didn't like the readings on my diode test from my meter, so I hooked up a bench power 20vdc, and a series 1kohm resister, and the diode zehnered at 3 vdc (bad...).  Got a new one coming (actually, 2; from Mouser).

I inspected the power amp board and found the TDA7294 power-amp chip is cooked (pic attached, hopefully).  Got a new one coming from Mouser.  I unsoldered it and removed it from the board in prep for the new one in a couple days.

I also hedged my bets on the 4560 dual op amps in the preamp circuit.  Since the -16vdc supply was bad, there is a good possibility that there is more bad stuff, so I ordered 2 new ones of them too. 

I don't know about the power-amp board yet though, since I don't want to power up without the -16v supply being properly "regulated".

Just having fun, and hoping it is not going to be too expensive to fix.   I also have not checked the speaker!  Oh, no, I hope it's OK. 

Here is a schematic emailed to me from Fender for a Fender 1270P powered monitor.  This is not DIY, but it is solid state...Interesting to see what they did.  So, I hope it's OK to post this here. 

I got this because I bid on Ebay (USA) and won a broken one.  (I should get the shipment tomorrow.)   I will be trouble-shooting and seeing if it is salvageable (and usable). 

I found this forum Googling while looking for schematics, and have had fun looking through what is here.  I downloaded the book from Teemu, but haven't had a chance to look yet (thanks for sharing!).

Not sure what I can add to the Forum, but can try to help with questions or trouble-shooting, and may post what happens with my monitor project.

Thanks for everyone who has been helping make and keep this Forum going.

Quote from: J M Fahey on April 29, 2008, 09:14:48 PM
Well, oliveaudio seems to have dissapeared from the net. Can anybody post those schematics, just for a curious look? Thanks.

The website is indeed gone, but the Google cached entry is still available, but without the graphics. 

I agree about wanting a curious look-see.  I assume that the schematics were downloaded by someone, so please can they be shared with us here?  Thanks.

Howdy.  How different is the Sunn from the Fender?  Fender bought Sunn, and I thought they might have just re-packaged the mixer, but may have used the same parts.

Here is the front and back of a broken Fender SR8520P powered mixer on Ebay currently (http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=190218660848&ssPageName=STRK:MEWA:IT&ih=009).  It looks very similar to your Sunn. 

Regarding the Ebay broken Fender, I thought about trying to buy and fix it, but I need a schematic to be sure (available from Fender in hardcopy, but takes how long?). Oh, and the seller wants $45 to ship it.