Yamaha A-960 troubles

Here is the Amp board. It is a corroded mess in some areas. Also one of the large 7500uf caps measures about 6900 the rest are over 7100uf.
I also noticed that TR 343 broke a trace underneath that I had to repair. It might have not been making a very good connection. I replaced it but it might have been jarred loose during all my testing .

But this is the negative TR I believe. I'll clean up the Glue and measure the resistors and check all jumpers that might have been compromised
by the corrosion.

The glue near the TR's that power the EQ board is much more burnt compared to the other Large cap glue.

I wonder if those caps were getting hot too and if they help power that +/- B1 line

The Pics.

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Denatured alcohol is not cutting it, I think I need to use acetone here.
 
So while working on cleaning up the Glue I decided to also change D328 to match D329 I changed out
from earlier . That one was bad. So as i was looking for the pins of the diode on the back of the board I noticed
that the solder joint looked funny. Here is what I found.


That whole PCB area was darkened a lot from the heat of TR 342 and TR 343 .

So I had these small heat sinks I added to the originals in hopes that it will help dissipate a little more heat.

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Now I am just cleaning up the old thermal paste and going to put the Main amp board back in.

Maybe that cold solder joint was the entire issue?

Athanasios
 
Are the zener diodes D328 (For the B1+) and D329 (for the B1-) okay? mine had bad voltages too on the phono which was caused by a bad zener diode, but mine is a A960II which has a different way of powering the phono. Are the TR342 voltages ok for the B1+? You've also got some other zeners D324-D327 in that section. I would make sure all are ok. Or better yet at $0.15 apiece just replace them. I'm not sure what they are, voltage wise.
Does your A960 have a connector from the main board to the phono board for the B+ and B-? My 960II does. Try unplugging it and checking the voltages again too. That would help determine if something on the phono eq board is loading down the B-.

I wish I could help more but I've never worked on an original model A960 and the schematic I found is very hard to read.


Just wanted to let you know that you were right on one of the Diodes. D329 was bad.

Also after cleaning off the glue I decided to replace the 7.3-7.7 Zeners ( HZ-7C2) . Well one was corroded so bad after removing
the solder i went to pull it and it left part of the leg in the through hole !! So those are now replaced.

I was thinking of moving TR342 and TR343 to the main heat sink's for the Amps.

That board is really burnt and it might have caused that cold solder joint on D328 from heating and cooling
every time the amp was used.

Nashou
 
I'm glad to see you are still at this. I probably would have given up a long time ago. I finished my 960II a while ago, with replacing the X2 capacitors in the power supply and recapping the whole thing, taking apart all the switches and sonic cleaning the metal pieces, deoxiting all the pots, replacing bulbs, some bad resistors in the power supply and I can't remember what else. Currently in the family room powering some small bookshelf speakers of I can't remember what brand, blasting christmas tunes for the family. Aside from the flaky cheap slider pots used, the rest of this amp is solid.
 
I'm glad to see you are still at this. I probably would have given up a long time ago. I finished my 960II a while ago, with replacing the X2 capacitors in the power supply and recapping the whole thing, taking apart all the switches and sonic cleaning the metal pieces, deoxiting all the pots, replacing bulbs, some bad resistors in the power supply and I can't remember what else. Currently in the family room powering some small bookshelf speakers of I can't remember what brand, blasting christmas tunes for the family. Aside from the flaky cheap slider pots used, the rest of this amp is solid.

Yeah the amp works just the Phono Section is dead. Something wonky is going on there and Mac and I can't nail it down.

Mac explains that at R139 the two opposing voltages should meet and then become 0 volts and its not.

At first we thought it was the + voltage was too weak current wise so that where i found the loose diode.
But i haven't tried to instal R137 and R138 that allow the voltage to get to TR107 and TR108's Gates. it is there where the over voltage or if a + voltage kills them.
 
Ok here is what I got.

I have TR 137 and R138 out to protect the J-Fets ( Tr 107 and 108)

On TR 109 and 111 along with the right channels same TR's I am getting only 11.98 volts on the Collector and Emitter respectively
for both Left and Right channels. SO I wanted to see what the voltages were if I removed R139 were suposedly the two opposing voltages meet to make 0
volts or close to it . I got these numbers after.

R154 was -10 and R153 is -7.xx

-B1 -10.53 and +B1 is 24.52

TR109 B +23.85 C + 23.62 E + 24.46

TR111 B +23.10 C -4,32 E +23.62

TR110 B +24.50 C +11.59 E +24.54

TR112 B +23.21 C -10.52 E +11.61

Read more: http://repairalmostanything.com/thread/491/yamaha-960?page=24&scrollTo=9136#ixzz4SgM2JVAI

Not sure where to go next. Mac has been just as confused as I am, and he hardly never gets stumped.

He thought it might be the servo amp section so I removed it all and the main voltages in went up to 48+/- volts .

So I put it all back in. also TR119 gets really hot. TR120 is next to it but I can't tell if it is too as they are too close to tell .

But here is a pic of that section with the parts removed.

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Athanasios
 
I think it might be fixed !!! Over at the Site MisterMac runs we had quite a bit of head scratching. Going back and forth
etc. Finally we decided to try to put the two resistors in that protect TR107 and 108 while we were testing. It seems that installing them makes the voltages all correct !!! But from the schematics and my feeble attempt to truly understand them I can't see how . ;)

But I did have a scare at first. On TR 108 the half that kept blowing( the outer half if looking at the board layout) i wanted to make sure after power up that the gate voltage stayed low on that half, well actually stayed at 0 . So I probed it as I turned it on. It started low in the mV's but then began to rise to over -1xx so I shut it down. looked over some things and tried again. this time it was on for about 4 minutes and it stayed in the mV's and I noticed that the servo amp stayed cool. TR119 and 120 were no longer hot as hell.

But the rise at the gate of TR108 had me scared so not sure if all is 100% well but the J-Fets are still good and the -/+ B1 voltages are fine for now.

More long term voltage testing tomorrow.

Athanasios
 
Well I think this one is filed under the repaired column !

Left the amp on for over 5 minutes and the 2SK363's remain functional !!! All voltages test out ok.

So next is some listening test and then I will decide if I should invest in new 2SK146's to replace the
2SK363's I used for testing because to their inexpensive cost. I fried a bunch along with Two and half 2SK146's.

I'll wait till i make another order at UTsource for another project and then order those as well to defray the shipping costs.

Been on this amp since MAY 2016!!!!

Next is the Sony TA 4650 V-Fet, That one I think I have ready for the V-Fets to go in.

Thanks for all who gave help and "good vibes" along the way especially MIsterMac.

Athanasios
 
Ok the Switch was bad so I ordered a new one and it works great. But another problem. No Phono , I did some searching around the voltages and found the -B1 line only at -9.95 volts . It should be -25.
So I discovered that TR343 only has -10 volts at the collector, the E and B are both around -50. So I have one coming in. This amp is a really nice sounding amp from what I tested so far. But it has lots of that damn glue
corroding some jumpers and other parts.

Athanasios
I was wandering if you recall where and which type switch you ordered for "Phono" since I have to exchange it on A-960 ( among other problems )
 
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I didn't change the phono switch. But here is a gold plated part, i believe the phono is shorter than the main direct and a 4 pole unit compared tot he 6 pole of the Main direct switch.

Data sheet where you can see which part you need. I used the FxUEE series

http://www.mouser.com/ds/2/60/Fpush_1nov12-221205.pdf

http://www.mouser.com/ProductDetail/CK-Components/F4UEE-AU/?qs=sGAEpiMZZMvxtGF7dlGNphL2x1aFDdTkb7y/IEIg0Ls=

they have cheaper ones for about 3 dollars not gold plated.

Nashou
Yes you are right, it's 4 contacts.
Thank you for the info
How this model sounds? Is it worth spending time and money on it - I have a few things to do on the one I got.
 
Yes you are right, it's 4 contacts.
Thank you for the info
How this model sounds? Is it worth spending time and money on it - I have a few things to do on the one I got.

It is a pretty nice sounding unit. Once you get all the small issues settled in the service bulletin etc it sounds nice.

So far I only spent time getting it up to working order and have not re capped etc. But it has a pretty decent phono section . It has plenty of power
for what I used it with. I think upping the main filter caps a bit would help a bit from what I have read in other places.

Athanasios
 
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