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Yamaha newbie A-700 resto thread

analogwisdom said:
CA-610 II that has a "fuzzy" right channel but otherwise good for $175, but I'd have to drive about 2 hours... Worth it or no?

I need to quit looking at for sale ads, lol.
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Your love for all things audio has turned into a full-blown addiction, LOL! Don't worry, it's not a bad thing – and you're in good company here at AK with like-minded folks. Just remember to share the wealth and let others enjoy some of those deals out there!
 
analogwisdom said:
I guess I could put everything together and test voltages with the dummy resistors in place. Not sure what I should be looking for, though. Any suggestions?
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I would compare left & ride side. Is one side good or is it a double chernobyl jones? The freebie A-700 SM I downloaded was pretty bad. Looks like you should have 70Vdc on the collector pad. I couldn't tell what the E-B dummy should read though. Does the SM you have show the E-B voltages? I think they should be the same values across the dummy as the SM, or close. But in case I'm the dummy; hoping a Sensei will chime in for a 2nd opinion, or just ask a Sensei directly. Most are real helpful and it is feel good Friday. Good time to ask.
 
Soundscape said:
I would compare left & ride side. Is one side good or is it a double chernobyl jones? The freebie A-700 SM I downloaded was pretty bad. Looks like you should have 70Vdc on the collector pad. I couldn't tell what the E-B dummy should read though. Does the SM you have show the E-B voltages? I think they should be the same values across the dummy as the SM, or close. But in case I'm the dummy; hoping a Sensei will chime in for a 2nd opinion, or just ask a Sensei directly. Most are real helpful and it is feel good Friday. Good time to ask.
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A-700 Schematic.pdf

drive.google.com drive.google.com

I scanned and uploaded my copy, here it is again just in case ya missed it. Way better than the HFE scan.

on TR139 looks like 71V on C, 70.8V on B, and 70V on E? and TR141 should be 71.8V on all three pads? It gets kinda cluttered and confusing around those spots.

and yes, both channels are out. There was nothing obviously burnt on the right channel but I still pulled everything and the outputs tested bad. I also replaced everything on the right that I did on the left channel just for posterity.
 
analogwisdom said:
I scanned and uploaded my copy, here it is again just in case ya missed it. Way better than the HFE scan.

on TR139 looks like 71V on C, 70.8V on B, and 70V on E? and TR141 should be 71.8V on all three pads? It gets kinda cluttered and confusing around those spots.
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Sorry my memory sucks. Nice copy man! I tuned out and worked on my piece & wife's transmission cuz ya had a bunch of pro's chiming in. So I missed a few thread pages.

By golly it looks like 70Vdc on every junction per schematic like ya said. The other pieces I've worked on had like half a volt DC @ E-B dummy so that's new territory for me. My A-1020 doesn't have those big MT-220 output animals.
 
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analogwisdom said:

A-700 Schematic.pdf

drive.google.com drive.google.com

I scanned and uploaded my copy, here it is again just in case ya missed it. Way better than the HFE scan.

on TR139 looks like 71V on C, 70.8V on B, and 70V on E? and TR141 should be 71.8V on all three pads? It gets kinda cluttered and confusing around those spots.
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Just wanted to recommend watching polarity. I noticed the collectors for TR139 are positive & TR141 are negative for example...the voltages look similar but are a world different. I've been guilty of over looking that aspect in the past but it might matter on this one after what happened to it.
 
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I'm waiting for some nylon screws/washers so I can mount the new TO-220-3 devices to the heatsink, but the A-700 is pretty much assembled and ready for me to test voltages with the dummy resistors in place once I can get the heatsinks properly mounted again.

I started a thread for my KA-3500 if y'all want to keep up with that too :)

Another KA-3500 restoration thread

Hey y'all. Welcome to the 3rd amplifier I've worked on. I'm a big Kenwood fanatic, and wanted something relatively simple, so I've had my eye on the KA-3500 for a while. I found this unit on Fleabay for a good price, of course the seller was a little enthusiastic about its operating condition...
audiokarma.org
 
analogwisdom said:
...on TR139 looks like 71V on C, 70.8V on B, and 70V on E? and TR141 should be 71.8V on all three pads?
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There may be (are) errors in the service manual.
The 22000uF capacitors are rated @ 69V max working voltage. 1000008635.jpg
From memory, the normal voltages on the 22000uF caps are approximately + & - 63V. The voltages will be lower when using the bulb limiter (mandatory).

Good Luck! You'll need it!
 
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analogwisdom said:
View attachment 3138332
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In the supplied picture, the Vbe multiplier transistor type is NOT visible (it may be a limitation of the camera). ALL the other heatsink mounted transistor types are clearly visible. It suggests that you've mounted the transistor incorrectly.
The metal tab (under the thin plastic coating) should face the heatsink - it's mandatory for good thermal tracking of the output transistors!
If you've mounted the transistor with the writing facing the heatsink, there may be an unexpected release of smoke if/when the mounting screw pierces the thin plastic coating covering the metal tab and the thermal tracking will be poor/non-existent (highly undesirable).

Good Luck!
 
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Hamish119 said:
In the supplied picture, the Vbe multiplier transistor type is NOT visible (it may be a limitation of the camera). ALL the other heatsink mounted transistor types are clearly visible. It suggests that you've mounted the transistor incorrectly.
The metal tab (under the thin plastic coating) should face the heatsink - it's mandatory for good thermal tracking of the output transistors!
If you've mounted the transistor with the writing facing the heatsink, there may be an unexpected release of smoke if/when the mounting screw pierces the thin plastic coating covering the metal tab and the thermal tracking will be poor/non-existent (highly undesirable).

Good Luck!
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Sorry, I am confused about this. Which transistor are you referring to?
 
analogwisdom said:
Sorry, I am confused about this. Which transistor are you referring to?
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The transistor(s) with the flying leads/small PCB attached. I don't have the circuit diagram available therefore, I'm unable to supply the transistor designation(s) - there's a Vbe multiplier transistor on each heatsink.

EDIT: TR125 & TR126 (from the picture in post 90).
 
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Hamish119 said:
The transistor(s) with the flying leads/small PCB attached. I don't have the circuit diagram available therefore, I'm unable to supply the transistor designation(s) - there's a Vbe multiplier transistor on each heatsink.
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I see what you're referring to now. I mounted them as suggested by Zaibatsu here,

A-700 Restore

• the 330uF for the phono section that you suggest is 25v, should I up that to 50v? I wouldn't. Keep it as close to original values as possible. Upping the voltage will likely increase the physical size. Some of those phono sections are pretty crowded already.
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but I will double-check the orientation I have mounted them in. They are TO-126 devices.
 
I don't think anyone is trolling me, if I fudge something up I want it to be pointed out so I can learn and correct the issue.

Just don't come after my WIMAs ;)
 
All I am waiting for now is my nylon screw/washer kit to get in and I am ready to start testing voltages in the A-700... itching to get this thing running, it should have been done a month ago... I went over it with a fine-toothed comb again today and it seems everything is ready to go, other than the heatsinks not being in... All transistors and capacitors are mounted and oriented correctly, every solder joint is re-done, the boards are de-fluxed, all of the inter-board cables are routed and connected properly...

Hopefully the mounting kit comes in tomorrow and I can start with the voltage testing.
 
Nashou66 said:
James you don't know stress till you fire up a V-fet amp the first time with the jewels installed. Thats is a harrowing challenge .

Nashou
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I'm never going to touch a V-FET amp with a 10 foot pole... the last thing this hobby needs is another newbie blowing up truly unobtainable/unreplaceable output devices... lol :angel:
 
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