Yamaha A-1000 DSBG

ic-racer

Super Member
I have had this A-1000 for about ten years but, for some reason, never got around to exploring it for DSBG. It started popping and crackling through the speakers so I brought it to the workbench for a DSBG overhaul.

One reason I'm posting is that the resistors near the DSBG can be hard to distinguish on the schematic. With glue on the resistor, the codes can be hard to see. Damaged resistors can read odd values. Blue can look like Gray and 6 can look like 8 on the schematic. One reason for the difficulty is that none of the carbon filament resistors are in the parts list.

Anyway, here are resistors and numbers that I replaced in case it helps someone.

All are Carbon Filament 1/4W 5% and about 6mm

R743 1.8k
R122 18k
R120 4.7k
R124 470r
R127 470k
 
r122.jpg
 
I've had the same trouble several times trying to read resistors that were covered in glue or just darkened due to age. Thanks for posting up some notes. The A-1000 is on my "definitely buy if I find" list so hopefully I'll be able to use the info in the future.
 
So when you get there, you first have to find the resistor number by looking at the PC board layout. The numbers of the CF resistors are NOT in the resistor list. So you have to scan the schematic for each resistor number to find the resistance.
 
Capacitors and resistors came today. Everything is installed and initial headphone listen is good. No more popping and it comes out of protection reliably in a few seconds each time I turn it on and off. Once it cools off I'll take some pictures and put to shell back together.
 
I ran into the same issue with my A-1020. I couldn't understand why after having ordering everything on the list I was still missing quite a few until Avionic pointed out the sentence in the upper left corner of the schematic stating that not all resistor values are included and to replace with the same value as you remove (or something to that effect).

Did you do a full recap or just replace the glue damaged ones?
 
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All the caps are probably still good but since they are out I got new ones. I got "MUSE" replacements for all except the largest two.
 
I put the new jumpers in first (ten total) then the resistors and finally the big electrolytics. One white polypropylene cap had goop but I could not find a similar looking replacement so I cleaned it and put it back.
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This is the vertical board on the right hand side. 4 caps (gold) and a jumper replaced here. These were a pain because I did not remove the board.
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Two caps, a resistor and jumper replaced here. New caps taller but plenty of room. Again audiophile "Muse" replacements were available from Mouser.
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This little resistor board bothered me ever since I got the amp. Looked burned. In my lifetime I have repaired equipment by replacing bad resistors probably 10 to 1 compared to bad capacitors. Anyway, for a few cents I got 20 new 27K 1/4w resistors and just replaced them all.
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Nice work. Looks quite a bit more packed in there than my later model.
I used some Muse and Silmics in mine when recapping. On checking through mine a good portion of the bigger caps were way under spec while the smaller ones and the large filter caps were still good. I replaced all of them but the filter caps since I was already in there and my amp had an unknown history.

Your amp looks amazingly clean in there btw.
 
New resistors in place. The old ones seemed OK (didn't check all 20, however). Not sure the reason behind this board. The resistors are in parallel. Maybe a super precise (due to averaging) high power resistor?
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To keep track of the original tiny resistors (there are no numbers on the PC board, and as mentioned the CF resistors are not in the parts list) I actually glued them to a printout of the layout. If they got mixed up, one might not ever figure out where they came from.
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Your amp looks amazingly clean in there btw.

Yes, this one was very clean when I got it. I'm the second owner. Originally purchased by a guy that worked in a local audiophile shop back in the 1990s. It was his main system and he took very good care of it.

My M45 came from a pawn shop and that one is a little rough around the edges.
 
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