SA-9800 Frys Speakers!

[ehc68]

I reviewed the thread and any PM's and we didn't do anything about replacing Q9 and Q11, correct?

No we didn't because I pulled them out and tested them and they seemed to be ok.

Q9 - Voltage on base and emitter was 680mv.
Voltage on base and collector was 680mv.
Nothing when reversing polarity on these.
Nothing on collector and emitter.

Q11 - Voltage on base and emitter was 598mv.
Voltage on base and collector was 598mv.
Nothing when reversing polarity on these.
Nothing on collector and emitter.


I will go ahead and start pulling and testing the transistors right now. I may have an answer in a couple of hours or so.

Don't sweat the mishap on the lead arrangements. I'm sure it's a lot easier to leave out details like that when trying to explain it than to actually be doing the work yourself. Checking details like that when you've done it so many times becomes second nature when doing the work yourself....so I completely understand.
I just ASSumed that on a cross reference that the lead arrangements would be the same. That's what I get for ASSuming!!:nono: :tears:

 

[ehc68]

Ok.....Q1 and Q7 tested fine, but I believe Q3 is a PNP so if I remember Echowars thread on testing transistors correctly, you reverse the polarity when testing these....right?
For example, I know on an NPN, you start out by testing (+) on base and (-) on emitter....and so on, so on a PNP isn't it (-) on base and (+) on emitter...and so on??
Without going back and reading his thread, I can't remember if this means on a PNP that the voltage drops are on different leads than on the NPN's.

If not, then it may be fried....here are the voltages of Q3 (ECB)....
.
Negative on base, positive on emitter - Nothing
Negative on base, positive on collector - Nothing
Positive on base, negative on emitter - Nothing
Positive on base, negative on collector - 680mv
Negative on collector, positive on emitter - 687mv

Then again, maybe this IS good, just the exact reverse of an NPN.:scratch2:

 

[ehc68]

I went ahead and soldered Q3 back in (I'm pretty sure it was ok) and Q2, Q6, and Q4 are still heating up!!:tears:

 

[markthefixer]

I went ahead and soldered Q3 back in (I'm pretty sure it was ok) and Q2, Q6, and Q4 are still heating up!!:tears:

RE: PNP vs NPN, yes reverse the polarities, voltages will be about the same.

I hope when you got the transistors, you got a few of each.

What was the voltage on pins 3 & 4, this is CRITICAL.... it is a FAST test, done before significant heat can develop, OR:

You will want to test Q2, Q4 & Q8 the same way as the other transistors (observing correct polarity), and IF you have Q2, Q4, Q6 & Q8 ALL out of circuit AT THE SAME TIME, you can power it up to check pins 3 & 4 for +52 volts.

One step at a time. First we get the +52 working, next we get the +32 working, THEN we get the -52 working and finally we get the -32 working.

 

[ehc68]

What was the voltage on pins 3 & 4, this is CRITICAL.... it is a FAST test, done before significant heat can develop, OR:

Ok, I turned it on real quick and checked pins 3 & 4 and they both read 76.6VDC.

You will want to test Q2, Q4 & Q8 the same way as the other transistors (observing correct polarity), and IF you have Q2, Q4, Q6 & Q8 ALL out of circuit AT THE SAME TIME, you can power it up to check pins 3 & 4 for +52 volts.

Do I still need to remove and test Q2,Q4, and Q8?

 

[ehc68]

This is the rough order of priority... :

+52 (on pins 3 & 4) is q1,q3,q7
+32 (on pins 5 & 6) is q9,q11

-52 (on pins 1 & 2) is q2,q4,q8
-32 (on pins 10 & 11) is q10,q12

I went ahead and tested pins 5 & 6, 1 & 2, and 10 & 11........

5 & 6 - are both 12.4v
1 & 2 - are both -19v
10 & 11 - are both -13v

 

[markthefixer]

Yes, IF they are heating up, remove Q2, Q4, Q6, Q8, Q10 & Q12 test Q2, Q4 & Q8 and leave out for a while.

Pins 3 & 4 have 76 volts instead of +52 volts. It's not regulating...
Now since Q1 through Q7 are all good and correctly installed, and the voltage is way over +52v , we NEED to read the individual transistor voltages. ESPECIALLY all three voltages on Q7 !!

Also read the voltage on pins 5 & 6, it should be +32 volts. edit: posts crossed, it's at 12.4, we need to check the D5 voltage...

The reference voltage developed by Zener Diode D5 (6.0 V) is also used by Q9 & Q11, which means that if they are damaged, they could affect the + 52 circuit. If the +32 is ok, then the D5 voltage is ok.

 

[ehc68]

Now since Q1 through Q7 are all good and correctly installed, and the voltage is way over +52v , we NEED to read the individual transistor voltages. ESPECIALLY all three voltages on Q7 !!

When Q2, Q4, Q6, Q8, Q10 & Q12 are removed, I can still check the voltages on Q1 through Q7 without them being affected.....right?

Also...I need refreshed on how to test diode voltages (for checking D5). I believe you told me back when you helped me with my sx-950 and I tried to look back through the old thread, and couldn't find it.

ALSO, can this too be accurately checked with Q2, Q4, Q6, Q8, Q10 & Q12 removed?

 

[markthefixer]

When Q2, Q4, Q6, Q8, Q10 & Q12 are removed, I can still check the voltages on Q1 through Q7 without them being affected.....right?

Also...I need refreshed on how to test diode voltages (for checking D5). I believe you told me back when you helped me with my sx-950 and I tried to look back through the old thread, and couldn't find it.

ALSO, can this too be accurately checked with Q2, Q4, Q6, Q8, Q10 & Q12 removed?

Correct.

In this case, the voltage is measured with the unit turned on, and the junction of D5 cathode and Q7's emitter is where to probe with the red lead, with the black voltmeter lead connected to chassis ground.

Correct again.

 

[ehc68]

Ok....time to fire up the 'ol soldering iron again!

I should be able to let you know the results either tonight or tomorrow.

 

[ehc68]

Ok....I pulled Q2, Q4, Q6, Q8, Q10 & Q12.

Here are the voltages of Q1 through Q7.

Q1) Emitter - 77.5, Collector - 78.5, Base - 78.0

Q3) Emitter - 78.5, Collector - 77.9, Base - 78.6

Q5) Source - 77.0, Gate - 01.7, Drain - 78.0

Q7) Emitter - 02.3, Collector - 01.7, Base - 01.6

Of course, this also makes the D5 voltage at only 02.3v as well.

I will test Q2, Q4 & Q8 tomorrow.

 

[markthefixer]

Try putting Q9 and Q11 back in, there are a few interdependencies in the sections, the current to drive D5 is tapped AFTER Q11 by R13, my bad.

Then see if the pins 3 & 4 get +52 v on them. If so, then re-taking the transistor voltage measurements is unnecesary.

 

[ehc68]

OK....well I'll let you know when I get the transistors and when I get them installed. In the meantime, I go ahead and solder back in Q9 and Q11 since they checked out ok.

They were already installed a while ago because they had tested out good. Should I remove them and test them again?

 

[markthefixer]

They were already installed a while ago because they had tested out good. Should I remove them and test them again?

Leave them in, and measure the voltages on Q9 and Q11, recheck the voltages on Q7 to see if they have changed...

The emitter of Q7 (same as the cathode of D5 and the emitter of Q9) should be at +6v, until we get that voltage there, nothing will make sense.

With Q2, Q6 and Q12 out of circuit, the negative voltages on the other side should not be getting through to affect anything.

The most likely suspect is C4 the 47 microfarad 10 volt capacitor being either shorted or leaky. The less likely suspect is R13, the 12k resistor supplying current to the D5 zener diode, C4 capacitor combination. That's what the Q9 & Q11 readings will help narrow down the problem. You could take an ohmmeter reading of R13 as well.

You COULD try removing (or better yet replacing) C4 and see if things start behaving themselves. There is a SMALL possibility that the circuit will oscillate without the presence of C4, but a quick check for 6v at the cathode of D5 without C4 in circuit (or replaced) may help.

 

[ehc68]

Leave them in, and measure the voltages on Q9 and Q11, recheck the voltages on Q7 to see if they have changed...

The voltages on Q9 is:
B - 02.3v
C - 12.9v
E - 01.7v

Voltages on Q11:
B - 12.7v
C - 72.9v
E - 12.0v

Voltages on Q7:
B - 02.4v
C - 01.7v
E - 01.7v

You could take an ohmmeter reading of R13 as well.

I tried to measure R13 and would just get the OL. reading. I switched through the KΩ range and still nothing. I touched a probe on each lead of the resistor...isn't that how it's done? Does this mean it's roasted?

You COULD try removing (or better yet replacing) C4 and see if things start behaving themselves. There is a SMALL possibility that the circuit will oscillate without the presence of C4, but a quick check for 6v at the cathode of D5 without C4 in circuit (or replaced) may help.

Ok, I removed C4 and the voltage at D5 cathode is 1.66v

 

[markthefixer]

Looks like R13 is the culprit, it should have shown 12k ohms. Without it, the zener diode isn't correctly biased (feed the diode, it's starved!!).

When the new 12k resistor goes in,
AND IF the +32 is on pins 5 & 6
AND the +52 is on pins 3 & 4

then all GOOD even numbered transistors can be re-installed, and the -32 and -52 supplies can also be tested.

 

[ehc68]

Cool!!
Ok....on this resistor replacement, do I need to know what the color bands represent or any other specs, or just ask for a 12k resistor? Edit: I could just bring in the old one and possibly match it up that way.

Would I be able to get this at radio shack.

I might as well replace C4 too while I'm at it. It's showing some discoloration as if it may have overheated at some point.

 

[ehc68]

I know it really doesn't matter, but I checked R13 with the amp OFF, and it read 3.28kΩ. It's obviously bad either way. Should the power be on or off when checking resistors?

 

[ehc68]

Well, I pulled R13 and tested it out of circuit and it's reading 11.96K.

 

[markthefixer]

I know it really doesn't matter, but I checked R13 with the amp OFF, and it read 3.28kΩ. It's obviously bad either way. Should the power be on or off when checking resistors?

power OFF !!! , if you did it with the power on, not only is the reading wrong, but you could have damaged the meter.


Lift one lead of the resistor from the pattern, then measure it to be sure ALL external influences have been removed.

3.28 k with the power off means there are external influences messing up the reading, plus 3.28k would supply too much current to the diode, possibly destroying it, depending upon the voltage on the far side of the resistor.

with this new information, I suspect the diode more now, but check the resistor with one lead lifted.

I need to check around, I may have some 6v zener diodes laying around (somewhere ara: )