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SA-9800 Frys Speakers!

I received the k34 today!!:D

Thank you VERY much Glen!!!!!:thmbsp:

ALL of you guys are the greatest. Really, I can't thank you enough!!!

If there's ANYTHING I owe you for this Glen, please don't hesitate to let me know!!
 
Before you power it up it wouldnt hurt to just go through
one last time and make sure all transistors are installed correctly.
Just to make sure the right pins are in the holes on the board.
Especially since you replaced some of them with transistors
that have a different pinout.
 
On top of the stupid bathroom, as i tried to get back on a few minutes ago my computer had a meltdown, I use a secondary slave drive for manual storage and almost everything else. Something went REALLY BAD, Now I just finally got the system to boot again by DISCONNECTING that drive... somehow the software fault blew something away on the drive that even affects the setup program!! Thus... I am almost operating blind, just some stuff i coincidentially printed out...

back to the sa-9800 ... what are the Q1, Q3, Q5 and Q7 voltages now?
which are original transistors? which were replaced etc...
we need a re-hash...
 
ehc68 said:
Voltages at pins 3 and 4 were both at 75.2.:thumbsdn:
Click to expand...

Keep in mind that pins 3+4 are actually tied together so will get the
same voltage from both.

I have a question,
Was there actually anything wrong with this board before the meter probe
accident?
 
ehc68 said:
Shortly after buying this amp (around 18 years ago) one of the channels (can't remember which one) started to become weak and amp started distorting.....then fried a pretty nice set of Technics speakers. It had been
sitting in storage ever since.

First of all...the protection relay engages as normal (or at least it did until the probe of my multimeter slipped.....read on).

The meter on the front panel of amp lights unevenly and will not light up at all
if the switch is set to "dim".
Right and left channel of the amps fluroscan display peak at 10.

The DC offset was:
Right channel - Bounces between -190.0mv to -210.0mv range.
Left channel - Same thing....-190.0mv and -210.0mv

Pins.....
1) -16.2v
2) -16.2v
3) 6.4v
4) 6.4v
5) 5.2v
6) 5.2v
7) 3.2v
8) 0 (black ground wire)
9) -78.0v
10) This is where it all happened. My meter probe slipped and shorted pins 10 and 11. When this happened, a CHUNK of plastic blew from a transistor (2SK34) located at Q5 and looked like there was smoke coming from some other part of the power supply board....maybe from what looks like to me a resistor (it has an insulation covering it). I didn't get a real good look because I quickly and frantically killed the power. It connects to pin 32.....illustrated in the pic). Before that happend, this would get really hot....too hot to touch.
After that, I wasn't about to turn it back on again to continue collecting the voltages until I checked in here first to see what to do for fear something else was going to fry. Take a look at the pic......
Click to expand...

He had something wrong, and got (and recorded) the first 9 pins worth of voltage readings before something else blew. the pins 3 & 4 as you can see were at 6.4 volts... BUT since he said the protection relay HAD been engaging, well, the fog of disaster had already descended...
 
markthefixer said:
What are the Q1, Q3, Q5 and Q7 voltages now?
Click to expand...


Q1
E = 74.1
C = 74.9
B = 74.5

Q3
E = 75.0
C = 74.4
B = 55.5

Q5
S = 74.4
G = 6.1
D = 55.5

Q7
E = 6.0
C = 6.1
B = 6.7


markthefixer said:
Which are original transistors? which were replaced etc... ?
Click to expand...

The originals are Q4, Q8, Q9, Q10, Q11, Q12.

The ones that were replaced were...

Q1 - Original was C1735, replacement is C1627.
Q2 - Original was C1735, replacement is D667 (from Mark).
Q3 - Original was A733, replacement is also A733.
Q5 - Original was K34, replacement is also K34 (from Glen).
Q6 - Original was K34, replacement is NTE459.
Q7 - Original was C1914, replacement is C2631.


Also Q2, Q4, Q6 were heating up again.....especially Q2.:dammit:
 
First, you can pull R2 for a while to protect the Q2 etc side.

Next I think from the voltage readings that Q3 may have been damaged.
It can be subbed with the 2sb716. (the only pnp i sent..)

2sa733 60v 0.15a .25w pnp with ecb layout
2sb716 120v .05a .75w pnp with ecb layout

I think the higher voltage is called for under fault conditions... and it isn't delivering anything near it's maximum current (which is less than the 733's) in this circuit.

For replacements, IF we buy any, we should go with higher voltage transistors, EchoWars's favorite, the ztx795a might do well here. it has a 140 volt rating, so fault conditions shouldn't faze it... the npn complement of the ztx795a is the ztx694b transistor. 140v .5a 1w both with ecb layout.
gain of 100 at .3A and 300 at 0.01A, which is fine for these circuits...
 
Ok....B716 is in, here are the voltages on Q3 NOW.

E = 75.8
C = 53.8
B = 75.3

The 50+ volts are now on the collector, when before they were on the base!

BEFORE (with A733 installed)

E = 75.0
C = 74.4
B = 55.5

One other change (hopefully for the better?) is that the watt indicator on the flouroscan display is not lighting up when before it would ALWAYS be at least at the 0.01 level (which on this meter is about 1/4th of the way lit up).

This may mean absolutely NOTHING at all, but at least it looked better.:D
 
When the b716 went into Q3, what were the voltages on the other transistors, did you check to see if they stayed the same, ESPECIALLY Q7.... I at least expected to see a pins 3 & 4 reading (this section could be FIXED for all I know) or something saying they stayed the same. If I had other readings I could judge whether or not we have additional damage induced...

Now Q1 looks shorted, but this piecemeal replacement could be hurting us rather than helping us.
Put the 2sd667 into the q1 position...

Either Q1 cures it, or we regroup, with voltage readings on current transistors Q1, Q3, Q5 & Q7 and reconsider what transistors are appropriate where...

for Q1:
2sc1735 100v .5a .8w npn with bce layout (original)
2sc1627 80v .3a .6w npn with ecb layout (possibly blown, inadequate replacement)
2sd667 120v 1a .8w npn with ecb layout (latest, robust replacement)

and recapping (rehashing) what WILL be in the circuit

Q1 replacement 2sd667 120v 1a .8w npn with ecb layout
Q3 replacement 2sb716 120v .05a .75w pnp with ecb layout
Q5 replacement 2sk34 same as original
Q7 replacement 2sc2631 150v .05a .75a npn with ecb layout

HMMM, that 2sc2631 was a GOOD choice with 150v breakdown!!
the higher voltages on q1 and q3 work to our favor, so Q5 becomes our weak link.

and rehashing our available parts... (so I don't have to search back 5 pages for it)
markthefixer said:
2x 2sd667 (Q1,Q2) 120v 1a 0.9w npn with ECB layout
2x 2sd756 (Q7,Q9) 120v 0.05a 0.75w npn with ECB layout
1x 2sb716 (Q3,Q4,Q8,Q10) 120v 0.05a 0.75w PNP with ECB layout (used)
Click to expand...
 
Sorry, I was in a hurry earlier and didn't have time to get all the readings to you....my days off are usually booked with something or another. Today is my daughter's birthday so we've been busy getting things ready for her party. The party is at 5:00, so I'll have to check more voltages a little later, however I'm not real sure what to do now, do you still want me to replace Q1 because......

pins 3 & 4 NOW are at 53.2!!!:D

I'll check Q7 as soon as I get back.
 
ehc68 said:
Sorry, I was in a hurry earlier and didn't have time to get all the readings to you....my days off are usually booked with something or another. Today is my daughter's birthday so we've been busy getting things ready for her party. The party is at 5:00, so I'll have to check more voltages a little later, however I'm not real sure what to do now, do you still want me to replace Q1 because......

pins 3 & 4 NOW are at 53.2!!!:D

I'll check Q7 as soon as I get back.
Click to expand...

If it ain't broke, don't fix it, leave Q1 alone..... and Q7... With it working, I don't need to know the voltages at those points enough to risk the measurements, now that it is working, the voltages are only a mild curiousity.

You don't have to rush on my account, I disappear offline for family stuff. It's the jumps ahead that I fear, sometimes documenting the next possible steps when the possibilities are so varied. Of course some folks don't have the luxury of a spot where the thing can sit open through the exchange... sort of like a chess by mail game.

with the +53.2 ok, check for the +32 and -32.. if they are there you can reconnect R2 and check that Pins 1 & 2 are at -53.2 (or so) volts.

Then we get back to checking those amplifier output offsets... and figuring out what happend to fry those speakers.
 
Mark....I finally have GOOD NEWS!!!

pins 5 & 6 = +32.4

pins 10 & 11 = -32.3

reconnected R2 and pins at 1 & 2 are -52.6


I think you may be about to win your game of chess!!:D
 
I'm getting the schematics ready, but one thing stands out, the regulation and tracking of the power supplies is CRITICAL for the offset adjustment.

In other words that 200 millivolts of offset you saw could have been directly caused by the power supply.
 
Well I checked the offsets and the right channel gradually climbed up to 18.5mv and the left channel climbed to 11.5 and was still climbing, but I felt I better shut the amp off because Q2 was getting HOT.

One funny thing I noticed was if I blew on the Q2 transistor the offset would go down dramatically then when I stopped, it would climb back up again.
 
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