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New 950 amp board update

Detailman

Detailman

Addicted to tweaking
Here I am again.
I've been working on this burned up 950 amp board for some time.
Finally got all together after a couple different parts orders.
First time I put it back together last week it got real hot when testing and setting bias. vr 1-2-3-4-.
Found out vr-3 was toast. Refer to this post for q's
http://www.audiokarma.org/forums/showthread.php?t=132968

I've replaced vr3 + 4 and meant to replace vr1+2 but ordered wrong for those. DOH
Anyway powered up and did adjustments on amp board per S/M.
Going fine. It's been running for 30min. or so and showing no signs of heating up. So far so good.
Couple questions.
Should I hear the relay click without the jumpers in?
I don't think so but I'm thinking my next step is to insert jumpers and then listen for relay and check dc offset.
At this point after a couple weeks work I don't want to make the wrong move now.
All transistors and caps on the amp board have been replaced along with a couple of other burned up parts.
All other boards except the tuner board have been recapped.

No smoke, no smells so far.
Just looking for guidance.

Thanks again.
 
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Check and set DC offset first, BUT with OR without pre-out/power amp in jumpers the protection relay will connect the speakers when conditions are favorable.

With bias being settable to spec, things are looking good.
 
Ok.
Trying to check bias with meter I pretty much get no reading.
I've put the jumpers in and with nothing hooked up I selected aux and pushed in A speakers. No click, no reading. Acts like my meter is not connected to anything. Same on B or C.
Bias was no problem to set especially with those multi-turn Bourns. Thanks for that.
Don't know where to go now!
 
If the protection relay doesn't click, the speaker terminals are NOT connected, thus NO reading of DC offset.

You have to read DC offset back on the amplifier board at pins (10 or 11) L? and (25 or 26) R?
note: pin# or pin# are connected together on the pcb pattern and either one is measured with respect to a metal chassis ground.

With as much as was done to the amps, the DC offset could be VERY high. Don't sweat it unless you can't get it to zero.
 
When I checked those pins as per the SM I could adjust them to like -1.5 or therabouts. Vr 1 + 2.
OK I was in bed but this was working my mind so I got up and did some voltage checking.
Schematic pg. 60 in my SM. 050board
Here is what I found
Pins 7,2,22,17,14,15,29 and30 were pretty much right on. volt or so here or there but in line.
When I first measured the pins all were ok but then in about 5 minutes I thought that I should check again. OOOPs

Pins 4,5 19 +20. were getting nothing this time. All the others were still the same. I went over them a few time to make sure it wasn't a meter problem.
I'm not real good a schematics but it looks like the subs for the 2sa726's aren't working or I put them in wrong.
Does that make any sense to you?
Also another q. I've got no wire connected to pin 17, 20 and 23. The voltages are there except for 20 which is tied to 19.
It's late and I've got to get some sleep but I'll start there tomorrow.
Thanks again.
 
The 2sa726's can't pull down pins 4,5 19 +20 enough to disappear the +36.5 volts. There are 62k and 82k resistors that limit the current drain at these points.

It is NOT an amp problem, it is a power supply issue.

I'm going to look back at what was done with Q5 and Q7 on the power supply board awr-101 on page 67.

Check to see if Q5 is getting hot.

edit: looks like the power supply was recapped, but I didn't find anything about the Q5 and Q7 transistors. Pioneer runs them hot. When there is enough room I recommend a bigger (to-126) transistor that can dissapate more heat.

it is: 512-KSC2682YSTU to-126 ecb 180v .1a 1.2/8w 200mhz 100-320hfe $0.31 ea
the original 2sc1318 is also an ecb layout
 
Notice by the time on your post that you couldn't sleep either.
Let me make sure I've got this straight.
Amp board is ok?

Check Q5 & Q7 on awr-101.
that 2682 part is what we ordered for the amp board and I did order 5 total
and have only used 2 so changing them is no problem.
Just a note. I had changed them to nte-289A when I recapped the board cause someone had replaced one with a tip-30. Same pinout ecb and it looks like I've got them right.
One step at a time.
 
I should have learned by now not to "take one last look" before passing out.

Yes, amp board ISN'T messing with the 36v, that 36v should be constant.

TIP30 is a PNP transistor, where was it? (Q2??) nte-289 is a NPN transistor, where WAS IT??

Q5 and Q7 are itty bitty to-92 transistors, only good for less (lots less) than a watt.

The 2682 is a rather high gain (320) low - power power transistor with a maximum current of 100mA or .1 amp. We are more interested in the fact that the case can dissapate 1.2 watts bare and up to 8 watts with a good heatsink. Q5 (21mA) is the one I was concerned with, the drain on Q7 (3.7mA) is less, but the Q7 drain passes through Q5 as well.

Running hot or too hot wears down a transistor over the years.
 
I hear you on one last look!!!!!!!!! LOL
OK
You were right on target. When I was recapping the ps board when I was using 950 as a pre-amp the tip-30 had been put to replace either 5 or 7.
Can't remember which now. Long while ago.
I had cross referenced them and got 289a and was making an order for something else so I ordered a couple.
Well rechecked them this afternoon and one was blown. Actually when I replaced them originally I messed up a trace and I now notice I did a lousy repair job.
Replaced both with 2682 pin outs are reversed. Now because I had ordered more 1142's from Mouser I went ahead and replaced the two complimentary 726's with the 1142's which are complementary to 2682.
Do you think that's ok?

I also found that post 10 wire from protection circuit was broken off from ps board. Now soldered back. I'm not sure if that was off before or I dislodged it when working on power supply.

I just thought of this. I've got one more 2682 and there is one more 1318 that I think I should replace also.
OK?

Didn't want to fire it back up till I got back to you.
Plus I need a little break. Didn't get a whole lot of sleep.
Be back later.

Thanks.
 
Detailman said:
Replaced both with 2682 pin outs are reversed. Now because I had ordered more 1142's from Mouser I went ahead and replaced the two complimentary 726's with the 1142's which are complementary to 2682.
Do you think that's ok?
Click to expand...

If those are the 2sa726's on the amp board, That's a substitution I would NOT have made.... I believe I said: 512-KSA992FBU (ln)to-92 ecb 120v .05a .5w 100mhz 150-800hfe $0.05 ea. I had HOPED to leave the 2sa726's ALONE, because those are a MATCHED pair... for best sound the gains should be as close as possible. The (ln) meant LOW NOISE... in a spot where that is IMPORTANT!! But the (ln) is less significant than the hassle in getting matched gain pairs, especially if your DMM does not do Hfe(gain) tests.


Detailman said:
I just thought of this. I've got one more 2682 and there is one more 1318 that I think I should replace also.
OK?
Click to expand...

On the power supply, there are three 2sc1318's; Q3, Q5 and Q7.
Q3 is NOT a problem as it is a feedback element and GAIN is important here, and the original may have more gain. There is little power being dissapated. Unless bad, leave it alone, it has NOT been stressed.
Q5 DOES dissapate heat and a 2682 here is a GOOD thing.
Q7 dissapates a lot less heat and with the low load on it, the subsitiution is not warranted but not harmful.

Detailman said:
I also found that post 10 wire from protection circuit was broken off from ps board. Now soldered back. I'm not sure if that was off before or I dislodged it when working on power supply.
Click to expand...

The relay would NOT have operated with it broken.
 
markthefixer said:
If those are the 2sa726's on the amp board, That's a substitution I would NOT have made.... I believe I said: 512-KSA992FBU (ln)to-92 ecb 120v .05a .5w 100mhz 150-800hfe $0.05 ea. I had HOPED to leave the 2sa726's ALONE, because those are a MATCHED pair... for best sound the gains should be as close as possible. The (ln) meant LOW NOISE... in a spot where that is IMPORTANT!! But the (ln) is less significant than the hassle in getting matched gain pairs, especially if your DMM does not do Hfe(gain) tests.

On the amp board I changed them with the 992's.
I did test for hfe and they were pretty close but I can put the old ones back in if necessary.




On the power supply, there are three 2sc1318's; Q3, Q5 and Q7.
Q3 is NOT a problem as it is a feedback element and GAIN is important here, and the original may have more gain. There is little power being dissapated. Unless bad, leave it alone, it has NOT been stressed.
Q5 DOES dissapate heat and a 2682 here is a GOOD thing.
Q7 dissapates a lot less heat and with the low load on it, the subsitiution is not warranted but not harmful.


I've changed Q3 + 5 but may change Q7 also with 2682.

On the power supply I changed the 720's with the 1142's not the 726's(I'm getting a little punchy) gave the wrong number the first time I believe.
Just looked like they should be complimentary to Q3 + 5.
If I'm wrong about that let me know please.



The relay would NOT have operated with it broken.
Click to expand...
Maybe that's a good thing.
 
Detailman said:
I have yet
Click to expand...

It's easy but tedious.

Detailman said:
to figure out how to
Click to expand...

I just do the quote, highlight the whole thing and control-c it

Detailman said:
seperate the quotes
Click to expand...

Then I just control - v it several times, and in each quote I just highlight and delete what I don't want.

Detailman said:
like you do
Click to expand...

The alternative is to copy everything in the square brackets for quote = to start a quote

Detailman said:
in your posts.
Click to expand...

and end the quote with the open-bracket slash quote close bracket

Detailman said:
And it's possible to insert text that was never there!!!
Click to expand...

See? :D

Of course I used to make my living telling computers what to do, down to the bits, bytes and chip hardware controls.
To me high level languages were an uncontrollable luxury, and I coded in assembly language and actual machine code.

I didn't just put the letter "A" on a screen, I constructed it with on and off dots.
 
Very cool. Now I get it.
On another note.
We now have tunes. I'm like a little kid in a candy store. Had to hook it up at this late hour even being tired. Couldn't resist.
Replaced all the 1318's on the ps board. Used the 1142's in place of the 720's.
Resoldered that wire from the protection board and turned the beast on to check and set the voltages.

Magic click appeared. Started my heart pumping.
Checked the dc offset and was in heaven. All three sets were between -1 or +1mv. Super clean.
I've been playing it for about 45min. with cable music for source and one side of Doobie brothers Vinyl.
Too early to make a judgement(sounds good) but with all the new parts I'm sure sound will change some with breakin.
Vinyl sounds great so far.

Running extremely cool. It's late and the wife is sleeping so I can't really crank it any but it seems very stable.

Can't thank you enough for your guidance through all this.
Very satisfying experience and lots of knowledge gained for me.
I'm grateful.

Only question I have and it's probably not important is that when I checked the voltages on the amp board three were just a little off.
Pin 7 schematic 51.5 Real 53.9
Pin 4 s 36.5 r 38.5
Pin 20 36.5 r 38.5

All the rest were within 1/10thV of schematic.

Gettin late again.

Back tomorrow.
 
Well with the bias well adjustable by the bourns multi-turn pots and the offsets within + / - 1 millivolt it's ready to rock.

The slight voltage variations are within 10 percent of the schematic values, You really can't hope for better than that with the tolerances of the components used. In other words, they are FINE!!!

Button her up, and let her sing!!!! after a week you may want to recheck the bias and offsets after things settle down (check them after at least 30 minutes of operation).

ENJOY the fruits of your labors!!!
 
markthefixer said:
Well with the bias well adjustable by the bourns multi-turn pots and the offsets within + / - 1 millivolt it's ready to rock.

The slight voltage variations are within 10 percent of the schematic values, You really can't hope for better than that with the tolerances of the components used. In other words, they are FINE!!!

Button her up, and let her sing!!!! after a week you may want to recheck the bias and offsets after things settle down (check them after at least 30 minutes of operation).

ENJOY the fruits of your labors!!!
Click to expand...

I would say fruits of OUR labor.
I've had it playing since this AM and it's getting better and better. I'm running everything flat.
Plenty of bass and lots of punch.
I thought the voltage was ok but wanted to check for sure.
The vinyl is excellent. Lots of detail and of course low end detail.

The only dumb thing I did was to order the wrong value for vr-1+2. You posted the correct value 10k but my copy of the SM says 1k.
I was an idiot for not looking at the pot itself.
I really like those multi turn Bourns. Can get it right on the money.
Those parts you suggested are sounding great.

Thanks again.

P.S. EW. If you read this thanks for showing me how to get to that amp board. Wasn't at all bad to work on.
Thanks.

I'm enjoying the sounds plus it's a pretty lookin BEAST!!!!!!!!!!
 
It would be nice to know the exact bourns number you ended up with, and a picture of the amp board with the bourns pots would be icing on the cake...

I am curious as to how much messing around you had to do to get the bourns pots to fit on that board and how well the leads and holes/pads lined up.
 
markthefixer said:
It would be nice to know the exact bourns number you ended up with, and a picture of the amp board with the bourns pots would be icing on the cake...

I am curious as to how much messing around you had to do to get the bourns pots to fit on that board and how well the leads and holes/pads lined up.
Click to expand...

This is the bourns I wound up trying.

652-3266p-1-101LF Mouser.

As far as fit goes it was pretty much right on. Just had to extend the legs out ever so slightly. It looks a lot smaller but seems great and I'm mad that I ordered 1k instead of 10k for the other vr's.
Next time I need some parts I'm going to order 10k and install.
I had ordered a few other types of cheapies for a choice but stick with the Bourns. Not that the others are bad but they were single turn.
Next time I open it up I'll snap a pic or two. These were square and actually I wanted a top adjust but they weren't in stock so I took these.
I can't remember if it's the P/N you recommended or not.

Take care
 
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