Pioneer SX-525 problems...

[mattsd]

Hi everyone!

I've been lurking around for a while and decided to join. I've had a very frustrating SX-525 that has been stumping me for awhile. I got it with both channels blown and through this thread: http://www.audiokarma.org/forums/showthread.php?t=269939 helped me with replacing the main amp board and power supply board transistors. I've replaced both of the 2sa489's and 2sc789's. I also replaced the 3 of the
2sc1318's. Every other transistor tested fine. I also recapped the power supply board and replaced the 2sd313. All the voltages test out fine on the power board.

I hooked the 525 up to a dim bulb tester and when turned on it goes bright as the caps charge and then dims, then starts to go bright again, and the output transistors heat up. I hooked a DMM to the speaker outputs and measured 11v dc before I switched it off so the transistors didn't heat up too much. I'm not sure what I should look for next, a bad cap? I've checked all the solder joints and proper transistor placement.

Any ideas? Markthefixer, do you have any ideas?

Matt

 

[markthefixer]

Did the thread mention setting the idle current?

Either way, turn the idle current 100 ohm pots down to zero ohms measured, then check the idle current.

For clarity, please post (or quote) anything pertaining to the idle current measurement so I can be sure we are talking about the same thing, before doing any adjustments!!

Eleven volts DC shouldn't have been at the speaker terminals. IF those a new output capacitosr (2200uf 35v), it should be remembered that a reversed capacitor acts like a short circuit. Any possibility one or both went in backwards? The available information in the past wasn't good - but it WAS better than nothing...

here's a link to the digital docs forum where a sx-525 manual scan has reportedly been posted.
http://www.audiokarma.org/forums/showthread.php?p=3931797#post3931797

edit: It's there, plus side of cap goes to output pin 9 (or 10 for the other channel).
minus side of cap goes to feedback pin 11 (or 12 for the other channel) as well as the speaker selector switch and the headphone resistors.

 

[mattsd]

Hey Mark, thanks for the reply and I'm sorry I was not more clear on what I've done.

First off, I have not replaced any of the main caps, they are still original. Also I have not recapped the main amp board or any of the others except the power supply as of yet. I also have the original service manual, so that is not a problem.

I've measured the idle current with the pots at zero ohms and this is what I've found.

Left channel: 383mv, way too high, and the tip42 (2sa489) gets very warm. The tip41 (2sc789) also gets warm, but not as much.

Right channel: starts at 50mv and went up 101.3mv before I shut it off because the tip41 was heating up. The tip42 also gets warm, but again not as much. Basically opposite of the left side, and I am testing these individually, one fuse out, the other in.

The above measurements are with it plugged into a dim bulb tester and are measured from shortly after power on till I have to shut it off because of the transistors. And as the transistors on both channels heat up the bulb starts to glow steadily brighter.

Is there anything else you would like me to do? I have really been wanting to get this thing on the road again.

Matt

 

[mattsd]

Update...

I went ahead and checked the voltages at pins 5 and 6 and got +33.2v dc for pin 5 and +43.1v dc for pin 6. This is with one fuse put in the left channel to measure pin 5 and then in the right channel to measure pin 6. With both fuses in the voltage on both pins was +32v dc. I also measured pin 17 and it also was +32v dc. Pin 18 had 5.5v ac to it.

Matt

 

[markthefixer]

That's due to the huge idle current demand.

Here's the procedure for measuring: get the test leads connected to the measurement points, then turn on the power and record the measurement, then turn off the power.

After a few measurements, we will remove the output transistors and leave them out until it is safe to install them.

measurement points, with zero ohms on both idle current pots:

first is the voltage between the bases of Q8 to Q10, best place to find them is at the D4 anode, and the 100 ohm pot on the opposite side of D2.

Second is the voltage between the bases of the Q12, Q14 output transistors.

Then repeat for the other side. Q7, Q9, Q11 & Q13.

After that disconnect the output transistors

Then repeat the measurements for both channels at zero ohms and then again for both channels with the pots dialed full on at 100 ohms on the idle current variable resistors. While the base leads will be disconnected, the voltages there are important.


edit: and just to be sure - no speaker loads or whatever...

 

[mattsd]

Here you go, Mark, are you ready

Output transistors in, pots at zero ohms:

Q8: +15.24V
Q10: +12.95V
Q12: +15.86V
Q14: +13.73V
Q7: +29.44V
Q9: +27.03V
Q11: +28.32
Q13: +27.24V

Output transistors removed, pots at zero ohms:

Q8: +18.89V
Q10: +15.96V
Q12: +17.54V
Q14: +17.01V
Q7: +37.24V
Q9: +34.35V
Q11: +36.90V
Q13: +36.05V

Pots at 100 ohms

Q8: +18.47V
Q10: +15.81V
Q12: +17.09V
Q14: +16.54V
Q7: +36.80V
Q9: +32.12V
Q11: +35.00V
Q13: +33.20V

I also noticed that Q5 got hot enough to burn, that is one of the c1318's I've replaced. Just to check I felt Q6, which was also replaced and it was cool.

Matt

 

[markthefixer]

<snip>

first is the voltage between the bases of Q8 to Q10, best place to find them is at the D4 anode, and the 100 ohm pot on the opposite side of D2.

<snip>

I'm sorry, I should have been more explicit, I meant for one voltmeter probe on one base and the other probe on the other base, to read the voltages differentially.

It is more accurate than trying to read the small voltage by subtracting two large voltages.

BUT I will analyze what's there, later tonight, as I have company over...

 

[mattsd]

Opps. Do you want me to get the readings between the bases of the transistors? I'm sure it will help you out, and it is not hard for me to get them back in real quick to test.

Matt

 

[markthefixer]

Opps. Do you want me to get the readings between the bases of the transistors? I'm sure it will help you out, and it is not hard for me to get them back in real quick to test.

Matt

yes please, but leave the outputs disconnected - just do the second part.

 

[mattsd]

Hey Mark, sorry I didn't reply last night, I got caught up.

Here are the voltages you wanted:

At 0 ohms:
Q7 and Q9 base readings: starts at 3.32V and drops to 2.63V
Q8 and Q10 base readings: 2.78V

At 100 ohms:
Q7 and Q9 base readings: starts at 2.65V and drops to 2.15V
Q8 and Q10 base readings: 2.44V

The Q8 and Q10 voltages are rock steady. The Q7 and Q9 voltages kept falling after the above measurements, but the measurements are at the point where it sort of leveled off. Also, which way are the pots normally supposed to turn to be at 0 ohms? Mine have to be turned all the way to the right to get 0 ohms.

Matt

 

[markthefixer]

That zero ohm and 100 ohm points seem to be acting opposite. Ohms are measured with power off. Zero ohms on the pot would be the minimum voltage base to base, 100 ohms would be the maximum voltage.

Q7 & Q9 have the problem, with Q8 & Q10 being rock steady.

I needed the Q11 to Q13 readings to go with the q7 to q9 readings

and the Q12 to Q14 readings to go with the q8 to q10 readings.

I'm scratching my head about the Q7 & Q9 readings starting off high and dropping.

 

[mattsd]

Okay, I just remeasured everything, because based on what you said, I think I made a mistake and sure enough, all the way left was zero ohms! Sorry about that.

So the above measurements need to be reversed, at zero ohms should be at 100 ohms. Q7 and Q9 base voltages also have leveled off after leaving it on for a couple of minutes: at zero ohms: 1.97v: at 100 ohms: 2.41v. Everything else was the same. This is with the outputs removed.

Here are the output transistor base voltages:

At zero ohms:

Q11 and Q13: started at 1.51v and fell to 1.30v, and kept falling, but I had to shut the receiver off because the tip42 was getting very hot.

Q12 and Q14: steady at 1.14v.

At 100 ohms:

Q11 and Q13: 1.41v and sort of steady, it kept falling but very slowly.

Q12 and Q14: 1.27v and rock steady.

I also noticed the dim bulb tester is acting up with the pots at 100 ohms, it went bright as the caps charge, dimmed then went bright, then went dim, bright, dim and then stayed at bright. At zero ohms the bulb goes bright, dims then slowly goes bright and stays that way. I tested the output transistors before putting them in and they were fine.

Matt

 

[markthefixer]

<lots of test instructions>

After that disconnect the output transistors

<more test instructions>

I have been going on the assumption that the output transistors have been removed as of 8/22/10 .

If they are still in, remove them. The amp will work WITHOUT SPEAKERS, even headphones could be too much of a load. But the measurements are valid.

When the bulb goes bright, I suspect we are in "thermal runaway".

Removing the output transistors (if one set "Q12 and Q14: steady at 1.14v." stays cool, they can be left alone and leave their pot at zero ohms for now) allows us to take measurements of what they are being told to do, without the bad effects of them actually doing it.

 

[mattsd]

Okay, I think I've been blind as well as stupid. What you have been trying to tell me is that I should take the base readings of the transistors without them in, basically put my test leads on the solder joints where the transistor bases go, correct? I, for some reason, have been interpreting as I have to put the transistors back in order to read the base voltages! I did have them removed, but when you posted this:

I needed the Q11 to Q13 readings to go with the q7 to q9 readings
and the Q12 to Q14 readings to go with the q8 to q10 readings.

I put them back in.

Please bear with me, I don't know what's going on with my brain right now.

Matt

 

[markthefixer]

<snip>
After that disconnect the output transistors
<snip>
While the base leads will be disconnected, the voltages there are important.
<snip>

I though maybe I should have worded that differently...

yes please, but leave the outputs disconnected - just do the second part.

Perhaps you are rushing, my posts are usually pretty complex and information dense, so read it slowly, think a bit to let it settle in, then re read it to see if your thinking and reading jibe..

This is why I dislike rushing, we (me too) all need time to .... think .....

 

[mattsd]

Yes, we all need time to, think And you are right, I have been rushing a little bit. I've been trying to figure this thing out on and off for two months now, and now that I have knowledgeable help, well...

Here are the base voltage for the output transistors with the transistors removed:

At zero ohms:

Q11 and Q13: 1.32v
Q12 and Q14: 1.23v

At 100 ohms

Q11 and Q13: 1.64v
Q12 and Q14: 1.56v

All the above voltages are very steady, unlike when the outputs were in.

Matt

 

[mattsd]

Hey Mark, something else I noticed, with the outputs removed and the voltmeter leads to the speaker terminals, the right channel has 4.00v DC going to it, and the left has 16.49v DC going to it.

Matt

 

[markthefixer]

Hey Mark, something else I noticed, with the outputs removed and the voltmeter leads to the speaker terminals, the right channel has 4.00v DC going to it, and the left has 16.49v DC going to it.

Matt

That should drop considerably with a 1000 ohm "speaker" load. otherwise the capacitors are leaking, so it is worth testing. The 1 or 10 million ohms resistance of the voltmeter allows the leakage current to attain a higher voltage reading than with more of a load.

Let's trade Q6 and Q5, and see if the voltages

At zero ohms:

Q11 and Q13: 1.32v
Q12 and Q14: 1.23v

At 100 ohms

Q11 and Q13: 1.64v
Q12 and Q14: 1.56v

stay the same.

The difference from 1.23 to 1.32 is quite significant here in terms of final idle current.

 

[mattsd]

Alright, I got the measurements for the "speaker" load and the switched transistors.

At 0 ohms

Q11 and Q13: 2.54v, and Q5 quickly got very hot.
Q12 and Q14: 1.36v

At 100 ohms

Q11 and Q13: 2.84v, and again Q5 quickly got very hot.
Q12 and Q14: 1.59v

Looks like I may have to get some new transistors.

For the speakers terminals: With the 1000 ohm resistor in place the left channel dropped to jumping between 30 and 34mv. The right channel dropped to jumping between 0-10mv.

Out of curiosity, I went ahead and removed the protection fuses and measured the voltages for the speaker terminals again, and measured 11.85v at the left channel and 80 to 100mv for the right channel. With the 1000 ohm resistor the left channel dropped to about the readings quoted above, and the right channel dropped to jumping between 9 and 70mv. Is it normal to measure voltages like that with the protection fuses removed?

Matt

 

[markthefixer]

Ok, to summarize, you swapped Q5 & Q6, and the problem did NOT move, and in fact got worse.

Removing those "protection fuses" shut down (deprived power from) most of the amplifier circuitry. No, not normal, meaningless.

edit, check with one leg each lifted: R23, R24, R25 & R26, particularly for an increase in value. Less current through D4-D2 & D1- D3 would result in an increase in their voltage drops, and I'm working blind because which transistor positions were the damaged transistors was never revealed to me. What is the pin 17 voltage, and the D6 cathode voltage?

man, that old thread has some bad karma that has bled through to here.

you mentioned following the thread. There were a lot of parts numbers missing, assumed and "unauthorized/unexamined/reverse-engineered" on that thread and I wish it would disappear.

I need to know exactly everything that has been replaced on the amplifier board, transistor number out and new transistor in, electrolytic capacitors changed etc... iiac we have a mix of new and old transistors. do we have a mix of zetex and fairchild transistors as well?

Q1 2sa572
Q2 2sa572
Q3 2sa572
Q4 2sa572
Q5 2SC1318
Q6 2SC1318
Q7 2SC1318
Q8 2SC1318
Q9 2sa720
Q10 2sa720
Q11 2sc789
Q12 2sc789
Q13 2sa489
Q14 2sa489
Q15 2SC1318
Q16 2SC1318

C1,C2, 1uf 25v cssa
C7,C8 220uf 35v cea
C9,C10 47uf 50v cea
C17,C18 2.2uf 50v cea
C21 10uf 16v cea
C22 220uf 50v cea
C23 100uf 50v cea
C24 47uf 50v cea

feel free to copy the above and edit (add on) the current status of the part.