Yamaha A-1000 Repair and Info Thread

Double checked orientation of everything? PNP and NPNs in right spots?

There may be a diode/zener that took a hit somewhere, I'd check the ones that are in the vicinity of the blown transistors (via the schematic). You can put your meter in diode mode and compare the equivalent part on the good channel to get a rough idea without pulling things out of circuit (just yet). I take readings in both directions. There usually an obvious discrepancy if you find something bad, ~10% usually means fine.

The other thing I do personally is take B-E and E-B resistance readings across any suspect transistors (in this case the ones you replaced) and compare to the good channel, if one has a bad diode going to it you'll sometimes see a discrepancy in those numbers. I diode test those junctions both ways too.

This is all with the amp unplugged by the way (no power, no DBT).

I'm sure avionic will have you check some live voltages when he chimes in, but I found those ^ checks sometimes expose the culprit in a low-risk environment, will give you something to do until he gets here.
 
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Double checked orientation of everything?

I am pretty sure they are in correct orientation. I pulled the old transistors that still worked and the good ones on the working side and put them on the component test thingy one at a time, and noted the opinouts, and double checked, then soldered them in. I can always pull them out but I am petty sure they are in correctly.

EDIT: checked again, just to be triply sure.. all of them are "label down" or the print side of the transistors on the board are facing west, if you had the unit oriented as it would be it you were in front of it using it normally.
 
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So to recap (puny of me):

I went and Re-Re-Re- verified that all the transistors are correct, and in the proper locations, and they are..I think. (see below). All were tested with component checker prior to soldering them in.

I went through and all the resistors are the correct values and I out them in the correct locations, and they were tested with a meter prior to soldering them in.

I went ahead and replaced the diodes for the phono/etc board, as i had to disconnect and pull it out to re-route some signal cables anyway. I did not test them before I installed them, for whatever reason, but I did verify that they were installed correctly. I just checked them in circuit with the meter and they seem to test fine. 1volt or so in one direction and 600mv or so in the other.

The Only thing that stuck out that I didn't notice before, is the NPN driver transistors that B&D sent me, are labeled differently than what they hand wrote on the package they bagged them in.
I ordered 2SC4793, and that is what is says on the baggy. the transistors themselves read C3749. I don't know if that is okay or not. Are those substituted for C4793?

That is where I am at in the troubleshooting process just so that everyone is up to speed. I am kinda leaning towards agreeing @zaibatsu and suspect a diode somewhere. Have not heard from @avionic yet, but I imagine he is busy. I will poke around some more after looking at the schematic this evening.
 
I ordered 2SC4793, and that is what is says on the baggy. the transistors themselves read C3749. I don't know if that is okay or not. Are those substituted for C4793?
I'll have to check -- stand by.....:yikes:
 
Massive overkill for (voltage and current) except for the (Ft) is pretty slow at 10 mhz compared to 100 mhz for the C4793's.
 
Whoa, that's a bit concerning IMO.
If fT is 10 surely hFE would be starting to fall well before that, and it's not the right complement for 2SA1837. I think it'd be good to get the right drivers before running the amp properly, though if avionic says it'll function in circuit, then I'd do those diode checks while you wait since it'll mean something else is amiss.

Those 2SC4793s have been gone from mouser for a long time now, wonder if there's a good modern sub for this pair?

I bet if you posted a thread in solid state someone would dip into their spares bin for you, I stupidly didn't stock up on those myself.

If you get stuck, I have 1 pair of the genuine A1306/C3298 pair I can mail out.
 
Well, if I ordered x and B&D sent me y in a baggy marked x would they not make it right and send me out some x if I talked to them? Or does it work differently in the electronics component world? Gonna have to look up there return policy...
 
Well, if I ordered x and B&D sent me y in a baggy marked x would they not make it right and send me out some x if I talked to them? Or does it work differently in the electronics component world? Gonna have to look up there return policy...

I would definitely hit them up for a replacement or refund (mistake on their part for sure), my concern was moreso that they may not actually have the correct part since they have been NLA for a while now.

If they do have the right parts then that would be great yes.
 
Well if things go south I may hit you up on the offer.

Since @avionic says the wrong one will technically work, that still leaves me try in to figure out what in the world is wrong with this thing..... At least it isn't trying to short circuit so I guess that is a plus :rolleyes:
 
I would definitely hit them up for a replacement or refund (mistake on their part for sure), my concern was moreso that they may not actually have the correct part since they have been NLA for a while now.

If they do have the right parts then that would be great yes.
BDEnt messed up my order one time. I ordered 16 MT-200 Sanken's and recieved 8 MT-200 and 8 MT-100 transistors. I called them on a real late friday afternoon. the person who answered the call was very pleasant and I got my other MT-200 transistors plus enough MT-200 mica insulators to do two M-80 amplifiers.Basically to ,more than, cover the postage to send the wrong transistors back.
 
Any Ideas on why the thing isn't working though? or do you all think the transistor is suspect Trying to follow schematic for nearby diodes but is that the most likely cause?

Any good places to start other than in the debris field?
 
If you do what I suggested with the B-E and E-B comparison tests L/R (I'd test both resistance and continuity value) across the transistors you replaced you might get a clue (re: whether anything else is wrong) and it'll only take you 5mins. This is with no power and amp turned off, safe as houses.

Personally I'd be patient until you find the C4793 driver to go in there, before moving forward with powered tests.
 
I usually always replace every diode in a damaged "chernobyl'd" channel including all zeners. Regardless what they test. But hey. Thats just me..:thumbsup:
 
B-E and E-B comparison tests so far:
Output Transistors OK
Driver Transistors OK
Bias Compensators OK
Predrivers: not so much. resistance for both NPN and PNP on the good channel is approximately twice that relative to the NPN and PNP on the bad channel..
 
...Any good places to start other than in the debris field?
If you can't find the failure during passive (powered-off - the safest method) testing, get some sleep and when you're refreshed, measure the various supply voltages (with power applied, obviously) etc.

The light bulb limiter must be used until the problem has been identified and corrected!

Engage the 'Subsonic Filter' as this will/should remove any DC voltage (from an internal/external source) being fed into the power amp input.
Set 'Auto Class A' and all other switches to off.
Power on.
Measure the plus & minus HB, LB and 22V (CRITICAL) rails. (These should always be documented)
Measure the DC offset at the junction of R263 & R265. and the junction of R264 & R266.
Switch off and check for hot semiconductors that shouldn't be hot. :yikes:

Post the results.

Good Luck! (And sleep well!)
 
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Engage the 'Subsonic Filter' as this will/should remove any DC voltage (from an internal/external source) being fed into the power amp input.
Please disregard the above statement - I was looking at the A-700 circuit and block diagrams. :oops: :oops:
The A-1000 SUBSONIC FILTER is NOT wired the same as the A-700 SUBSONIC FILTER, and according to the block diagram, will NOT remove any DC voltage induced by errors in the FLAT AMP and TONE CONTROL circuits from the power amp input.
My humble apologies for the misleading and erroneous information. :oops: :oops:

Good Luck!
 
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