Pioneer SX-525 problems...

[markthefixer]

Yes, I can do it with the 100 watt, I just had the 40 watt in to catch shorts faster.

Measurements with the 100 watt:

Minus side of C21: 0.4mv DC

Power off, check resistors:

R46: 32.9 ohms
R47: 14.81K ohms

Update!

Hold the phone, I think I might have found the problem, or one of them. I discovered the glass covering on D5 was cracked and splintered, so I went ahead and de-soldered one leg to test it and when I pulled gently on the leg with pliers, the whole diode snapped in half! So now I need a new diode, any suggestions?

Matt

Got a Radio Shack nearby? although their parts department has deteriorated to pitiful, they still have some useful diodes:


1N4004 Micro 1-Amp Rectifier Diode
Model: 1N4004 | Catalog #: 276-1103 $0.99 (for three I think).

if they don't have the 4004's, anything from a 4002 through 4007 will work.

 

[mattsd]

Yes sir, as a matter of fact, I have about 14 or 15 of them in my collection of parts that I have been slowly gathering. I found that most of the receivers I've repaired need them.

You are aware the original D5 was a zener, correct? I just trying to make sure I don't put in a wrong component.

Matt

 

[markthefixer]

Yes sir, as a matter of fact, I have about 14 or 15 of them in my collection of parts that I have been slowly gathering. I found that most of the receivers I've repaired need them.

You are aware the original D5 was a zener, correct? I just trying to make sure I don't put in a wrong component.

Matt

HUH??????????????

Where, in the name of Nikola Tesla did you get THAT idea?

The only zener in the unit is the 32v zener D6 in the power supply.

That is a signal diode, 70v reverse and 450ma forward current. Glass = zener is NOT applicable....

I am intimately aware of the functions in that circuit, and a zener diode would really screw things up.

Just use the 4004 - or anything close...

 

[mattsd]

Okay, maybe this will help you see what I'm seeing. My schematic shows this as D5.

First is where it came from, the second is the part. Board photo is with the receiver tilted on its left side.

Matt

 

[markthefixer]

That signal diode, used to rectify the 8v ac CAN be a glass diode and still not be a zener diode. Following the pattern and nearby components, it is the diode I expected it to be. The 4.7k nearby and the - terminal of that small cap confirm it.

Just because the 4004 is an epoxy case rated for even more heat does not disqualify it from being used there.

The symbol on the board is for a conventional diode, not a zener which would have small "arms" waving up and down off the main "target" line.


All is well, use the 1n4004... it's 1 amp and 400v, the old diode was less than half an amp and 70 volts iirc

 

[mattsd]

I will do that. Please forgive me for harping on this, I just wanted to make sure that I wasn't putting in something that might blow stuff up. I learned that lesson the hard way, so I'm cautious.

Thank you very much for all that you have done so far, we will get this thing fixed!

 

[mattsd]

Here are the measurements again, and I think we are on the right track.

Q5 Base: 0.579v
Collector: 22.88v
Emitter: 0.5mv

Q6 Base: 0.572v
Collector: 22.70v
Emitter: 0.5mv

D6 Cathode: 46.6v

Minus side of C21: 8.47v DC

Pin 18: 7.45v AC

Pin 17: 48.6v

Q7 and Q9 base at 0 ohms: 1.90v
Q8 and Q10 base at 0 ohms: 2.36v

Q7 and Q9 base at 100 ohms: 2.24v
Q8 and Q10 base at 100 ohms: 2.72v

Q11 and Q13 base at 0 ohms: 0.805v
Q12 and Q14 base at 0 ohms: 1.33v

Q11 and Q13 emitter at 0 ohms: 0.00v
Q12 and Q14 emitter at 0 ohms: 0.00v

Q11 and Q13 base at 100 ohms: 1.11v
Q12 and Q14 base at 100 ohms: 1.58v

Q11 and Q13 emitter at 100 ohms: 0.00v
Q12 and Q14 emitter at 100 ohms: 0.00v

Q15 base: -1.14v
Collector: 47.6v
Emitter: 0.2mv

Q16 base: 47.6v
Collector: 48.4v
Emitter: 47.6v

Please let me know if there is any other readings I need to do, though I think this is pretty complete.

 

[markthefixer]

Ok, with new transistors we still haven't gotten the idle current adjustment similar. The adjustment range is close (0.48 vs 0.46), but the starting point is too high at 2.36 iiac.

Q5 Base: 0.579v
Collector: 22.88v
Emitter: 0.5mv

Q6 Base: 0.572v
Collector: 22.70v
Emitter: 0.5mv

Q7 and Q9 base at 0 ohms: 1.90v
Q8 and Q10 base at 0 ohms: 2.36v

Q7 and Q9 base at 100 ohms: 2.24v
Q8 and Q10 base at 100 ohms: 2.72v

BUT Things are getting better

Q5 Base: 0.579v
Collector: 22.88v
Emitter: 0.5mv

Q6 Base: 0.572v
Collector: 22.70v
Emitter: 0.5mv

first check the 4 18 ohm resistors, R17,28,29,30
and the 4 150 ohm resistors R31,32,33,34

If they look good in circuit, then you don't have to lift a leg for now, but if it is EASY to lift the legs, it would be preferred on the off chance that the correct reading would be masked.

If one is more than 20 % off then hold off on the stuff below:

Then I need ground referenced voltage readings from both sides of, and differential readings across R23, R24, R25 & R26
and
ground referenced voltage readings of eb & c on Q7/ Q9 and Q8 / Q10 and pins 7, 8 , 9 , 10.

All these are at zero ohms for now.

This will allow me to profile the two sections each of both channels at the same time.

Basically Q8 and Q10 are still too high, and would give the unreasonably high idle currents.

 

[mattsd]

Here we go!

R23: Voltage 1: 47.2v
Voltage 2: 43.3v
Across: 3.96v

R24: Voltage 1: 47.3v
Voltage 2: 43.3v
Across: 3.95v

R25: Voltage 1: 43.3v
Voltage 2: 24.98v
Across: 18.47v

R26: Voltage 1: 43.4v
Voltage 2: 25.30v
Across: 18.10v

Q7 Base: 25.02v
Collector: 49.1v
Emitter: 24.46v

Q9 Base: 23.10v
Collector: 47mv
Emitter: 23.63v

Q8 Base: 25.30v
Collector: 49.1v
Emitter: 24.74v

Q10 Base: 22.98v
Collector: 72.4mv
Emitter: 23.52v

Pin 7: 0.1mv

Pin 8: 0.1mv

Pin 9: 24.05v

Pin 10: 24.09v

Edit: almost forgot to add, all the resistors tested to within 5% of stated level, and I tested all of them out of the circuit.

Your turn!

 

[markthefixer]

I'm in the process of crunching numbers, but if you could measure the voltages across D1, D2, D3, D4 it may be crucial.

 

[mattsd]

Here are the diode voltages

D1 Voltage 1: 23.26v
Voltage 2: 23.00v
Across: 209.9mv

D2 Voltage 1: 23.63v
Voltage 2: 23.04v
Across: 0.692v

D3 Voltage 1: 25.00v
Voltage 2: 23.26v
Across: 1.680v

D4 Voltage 1: 25.28v
Voltage 2: 23.63v
Across: 1.660v

 

[markthefixer]

D1 is bad, it's a 1s2076 which is a general purpose diode. 450ma 30v

It is used for it's voltage drop. it should be 0.6v or so.

Please swap it for another 1n4004.

If you have some small glass diodes, let me know the numbers and I'll see if they are substitutes.

The 4004 doesn't have reverse recovery time specified, so it is slow
BUT
It isn't reversed in this application, so the 4004 will do fine.

after the diode is in, do these:

Q7 and Q9 base at 0 ohms: 1.90v
Q8 and Q10 base at 0 ohms: 2.36v

Q7 and Q9 base at 100 ohms: 2.24v
Q8 and Q10 base at 100 ohms: 2.72v

once more.

You COULD skip a step and put the outputs back in, and SKIPPING THE 100 OHM CHECK, check the voltages and then also idle current at zero ohms, then CAUTIOUSLY while watching the idle current, turn up the idle current (increase the resistance) from zero ohms and see how it behaves.

Somewhere back in the thread we may have cured the escessive idle current problem, and just revealed the bad diode. Luckily the 1.6v stv diodes were not harmed.

 

[mattsd]

Here you go!

I replaced it with a 1n4004, as I did not have any glass diodes.

Q7 and Q9 base at 0 ohms: 2.31v
Q8 and Q10 base at 0 ohms: 2.36v

Q7 and Q9 base at 100 ohms: 2.67v
Q8 and Q10 base at 100 ohms: 2.72v

If these check out all right, should I put in the outputs?

 

[markthefixer]

Here you go!

I replaced it with a 1n4004, as I did not have any glass diodes.

Q7 and Q9 base at 0 ohms: 2.31v
Q8 and Q10 base at 0 ohms: 2.36v

Q7 and Q9 base at 100 ohms: 2.67v
Q8 and Q10 base at 100 ohms: 2.72v

If these check out all right, should I put in the outputs?

Yes, put in the outputs

 

[mattsd]

Okay, good news and bad news.

The good news, music! This thing, even through the junk speaker I was using, sounded gorgeous.

The bad news, the idle current is too high. It's hovering around 75-80mv on each channel, and I have at zero ohms. I measured the current from start up and the right channel starts at about 40mv and goes up. The left channel starts at 25mv and goes up, as a result, the transistors after about two minutes become hot to touch, the right side heating up faster then the left. So it looks like another thermal runaway.

I did put it back on the 40 watt bulb, could the reduction in input voltage cause it to do this? Or are the outputs damaged from the previous times that they were in? The 40 watt does what it did before, goes bright as the caps charge, then goes dim and slowly grows bright, and right about the time the transistors are hot to touch, it levels off and stays at the same level. Turning up the idle current causes the bulb to glow very brightly, cutting off most of the input voltage.

Should I use the 100 watt, or what? Here are the Q7, 9, 8 and 10 voltages at the time the transistors got hot with the 40 watt in place.

Q7 and Q9 base at 0 ohms: 2.32v
Q8 and Q10 base at 0 ohms: 2.36v

 

[markthefixer]

Measure the R25 and R26 differential voltages again, (across them), so I can calculate the diode currents. Also the DC voltage across the speaker with no sound (leaky capacitor from post #1??)

Did we / you ever replace the electrolytic caps?

We can try shorting out D1 and D2, which will reduce everything, and hopefully the 0 to 100 ohms and 0.3v adjustment range will give us enough leeway to hit the idle current.

The tip41 and tip42 transistors from the other thread that you purchased, were they On-Semi (863-)? Or Fairchild(512-)?

I really don't get it, we're just about back to factory new on this, all the resistors have been checked ok, and BOTH channels are doing it.

IN the past I have used On-Semi mje15032 and mje5033 transistors in the driver stages of the 3900's amp and I had high bias problems there too, until I put in Fairchild transistors. I wonder if these On-Semi transistors also have a slightly lower turn on emitter to base voltage that is biting us in the you know what...

edit- I just checked the old thread, (863-) On-Semi... we could try using other tip-41/2's (512-tip41b, 512-tip42ctu) but shorting the diodes is faster.

edit 2 - why did I fixate on tip41/2's? the originals are 60v 4a 30w 40-240hfe 3mhz transistors....
512-KSB596OTU pnp to-220 bce 80v 4a 30w 3mhz 15-240hfe $0.62
512-KSD526O npn to-220 bce 80v 4a 30w 3mhz 15-240hfe $0.62
would do fine...

edit3 use:
512-KSB596Y pnp to-220 bce 80v 4a 30w 3mhz 15-240hfe $0.62
512-KSD526Y npn to-220 bce 80v 4a 30w 3mhz 15-240hfe $0.62
I grabbed edit2 from an old post, these are the in-stock numbers...

 

[mattsd]

Did we / you ever replace the electrolytic caps?

No, I did not replace the big caps yet. It is possible that they leaking, but you had me put a 1000 ohm "speaker" load in the terminals and here are the results:

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.

However this is before replacing the caps and transistors on the board, so here is what I am measuring now:

Left channel: Jumping between 10 and 50mv
Right channel: the same as above

It jumps around so much it's almost impossible to read.

Here are the resistor voltages:

R25: 14.80v
R26: 14.80v

Edit: Just found your second edit, should I use those? Also, I did use ON tip 41 and 42. Get your information straight, Matt

 

[markthefixer]

Do the diode shorting thing to cut the idle current. Roger the On-Semi TIP's... (DRAT!!!)


14.80 v / 4700 ohms = 0.00315 mA

0.00315 mA x 100 ohms = 0.315 volts adjustment range.


re: 10 to 50mv jumping around... harmless but if you redo the electrolytic caps, get the output caps too.
(that WAS with zero volume? right?)

 

[mattsd]

(that WAS with zero volume? right?)

Yes it was.

Okay, I shorted the diodes, and it solved the overheating, but even with pots turned all the up I could get only 0.1mv of idle current on both channels, but I assume that is normal with the way it is configured. With the pots at 0 ohms the idle current was a flat 0mv.

Edit: also, the power transistors you suggested are discontinued, will these work?

512-KSD526Y npn to-220 bce 80v 4a 30w 8mhz
512-KSB596Y pnp to-220 bce 80v 4a 30w 3mhz (min)

 

[markthefixer]

Ok, that is progress.

Either we add resistance (another 47 to 100 ohms fixed resistance) or change the outputs to the KSB/D transistors I mentioned.

My numbers are old... let me check...

I grabbed those old numbers from an old post, these are the in-stock numbers that I maintain in my master list.......
(da%$ shortcut bit me in the A!! again)
512-KSB596Y pnp to-220 bce 80v 4a 30w 3mhz 15-240hfe $0.62
512-KSD526Y npn to-220 bce 80v 4a 30w 3mhz 15-240hfe $0.62