Marantz PM-66SE Burns Transistors

[petehall347]

Re: Marantz PM-66SE Burns Transistors

quickly get voltages at bases of q754 q756 .
on another note do have the means to connect a series light bulb to the mains power to limit the current ?

[hyva_ana]

Re: Marantz PM-66SE Burns Transistors

Q754, first rises to about -12V then starts dropping.
Q756, first rises almost -17V then starts dropping.

I have to build that light bulb current limiter.

[eccerr0r]

Re: Marantz PM-66SE Burns Transistors

Seems Q754 Q756 and Q758 should be in cutoff but they're not ... somehow Q758 is shorted or has the wrong polarity?
Check the npn/pnps carefully if the transistor still tests good...

adding original board photo to this thread too...since icloud is so slow for non apple users apparently.

[hyva_ana]

Re: Marantz PM-66SE Burns Transistors

Now I tested all of these transistors:

Q757, Q758
Q753, Q754
Q751, Q752
Q755, Q756
Q759, Q760

All of those are good and in right position.

[hyva_ana]

Re: Marantz PM-66SE Burns Transistors

And now:
QN01, QN02, QN03
Q701, Q702, Q703, Q704
Q801, Q802

This means that whole board is stripped out of transistors, and none of them is faulty (or at least not shorted). How close these small transistors (2SC2240 and 2SA970) should be each other in terms of gain?

[eccerr0r]

Re: Marantz PM-66SE Burns Transistors

Put all the transistors back except Q757-Q764. you should be testing at steady state - after everything settled. When you mentioned -12V@B(Q754) and -17V@B(Q756) this was a bit large of a differential but should be okay - as long as the difference between the two pins stay less than 4v or so apart after settling. According to the schematic they should settle to 3.4V difference or so, 1.7V each to GND when idling/silent.

At the next stage with Q758/Q760 installed, their bases need to be within 3v of each other. It says 2.4V or 1.2v to GND at idle/silent.

The gains of Q753-Q764 don't matter very much, they just need to work as transistors.

[hyva_ana]

Re: Marantz PM-66SE Burns Transistors

Now those transistors are back in their places, except Q757-Q764.
Q754 @B 17.8V, Q756 @B 14.5V
Q758 @B 17.8V, Q760 @B 14.5V

I don't know if I'm just too tired or what, but I could almost swear that when little earlier I measured those bases of Q754 and Q756, the voltages were negative, and now those are positive...

But now, state is steady.

[eccerr0r]

Re: Marantz PM-66SE Burns Transistors

17.8V-14.5V=3.3V so this is actually good for Q754/Q756 but its absolute value should not be so high unless there's an input bias (are you shorting the inputs to 0v during testing?)

With the voltages at 14-17v, Q756 and Q760 should be cutoff, but you're saying the B-E junctions of Q754 and Q756 are 0 volts difference and thus shorted?

R762 is in place? Did it fry?

What is the voltages at Q702 and Q704 (B,C,E)? In any case the voltages on the drivers are looking like they shouldn't cause the drivers to fry unless the wrong devices were inserted or pins swapped.

[hyva_ana]

Re: Marantz PM-66SE Burns Transistors

I'm taking a few days off from this project. I'll get back to it soon.

[hyva_ana]

Re: Marantz PM-66SE Burns Transistors

17.8V-14.5V=3.3V so this is actually good for Q754/Q756 but its absolute value should not be so high unless there's an input bias (are you shorting the inputs to 0v during testing?)

With the voltages at 14-17v, Q756 and Q760 should be cutoff, but you're saying the B-E junctions of Q754 and Q756 are 0 volts difference and thus shorted?

R762 is in place? Did it fry?

What is the voltages at Q702 and Q704 (B,C,E)? In any case the voltages on the drivers are looking like they shouldn't cause the drivers to fry unless the wrong devices were inserted or pins swapped.

Back again.

What exactly you mean by this: are you shorting the inputs to 0v during testing?

Q754 B-E: 0.62V. Q756 B-E: 0.58V

Components that warms up: Q763, Q764 (1k resistors between B-E), Q756, Q760, Q704, Q703 (warmest), Q728, R732.

R762 is in its place and not even getting warm.

Q702 B: 22.6v; C: 18.6V; E: 23.2V
Q704 B: -16.7V; C: 13.9V; E: -17.2V

Those are readings when I'm driving that board with two in series connected BPS, with voltages marked back side of the board: +24V and -18V.

But, when I connect board into its own transformer, that gives +/- 41.6V and then things are getting really hot. Especially those 1k resistors connected between B-E in Q763 and Q764 gets burning hot almost immediately.

What is the "right" way to try to figure this thing out?

[alfatv]

Re: Marantz PM-66SE Burns Transistors

Check C-E of Q801, Q802, they are probably shorted.
Then check the voltages from attached screenshot.
+24V and -18V must be there otherwise something else is wrong with those regulators.

[hyva_ana]

Re: Marantz PM-66SE Burns Transistors

Check C-E of Q801, Q802, they are probably shorted.
Then check the voltages from attached screenshot.
+24V and -18V must be there otherwise something else is wrong with those regulators.

Those are not shorted.

Q801: B 24.4V; C 41.0V; E 23.8V
Q802: B -18.0V; C -40.3V; E -17.5V

[alfatv]

Re: Marantz PM-66SE Burns Transistors

OK, but +24V and -18V are not the only voltages. +/-38V are used for the amp.

[petehall347]

Re: Marantz PM-66SE Burns Transistors

i think something is wrong at around q752 q702 q722
get voltages for those 3 .

[hyva_ana]

Re: Marantz PM-66SE Burns Transistors

Q752: B and C; voltage rises to about 26V for a little while and then rapidly drops to about 10 V, then it drops more slower towards zero - the lower it get's the slower it drops. But, when I cut the power off, the voltages rises rapidly to about 15V, and then drops to zero within couple of seconds. This same thing applies to Q702 collector.

Q752: E -25.6V

When I measured voltages again from Q752 E, it goes first to about +22V, then it rapidly drops to couple of volts and then slowly to zero and from there to negative voltage (increases slowly). Now when I cut off the power, voltage jumps to about +10V, the drops to couple of volts, then suddenly goes to -3V and jumps around, till it gets to 0V or something like that...


Q702: B 40.3V; E 40.8V

Was that Q722 a typo? I strongly think that there are no such transistor on that board.

[petehall347]

Re: Marantz PM-66SE Burns Transistors

i meant q704
see what voltages for other channel as well

[hyva_ana]

Re: Marantz PM-66SE Burns Transistors

Here are some voltages:
https://www.badcaps.net/forum/pictur...&pictureid=968

Now all the voltages were pretty stable, unlike on earlier measurements. Things really seem to change on this amp board...

I don't know much of these, but I just wonder those QN03 voltages, or especially collector voltage.

[eccerr0r]

Re: Marantz PM-66SE Burns Transistors

if E-Q752=-25.6V and C-Q752=26V to 10V to 0V, this transistor is not working properly. If the transistor is working and not getting hot, this would imply R752 is broken.

However I'm worried about measurement errors as the numbers reported post 35 are different in post 30 for Q702.

I do apologize for all helping, we sometimes ask people to do things over and over again whether by mistake or TLDR, but sometimes this does show some measurement errors and without accurate measurement we can't deduce what's wrong.

When I said input shorting, I meant the inputs to the entire amplifier - just want to make sure you didn't have some signal, especially one with a DC offset, going into the amplifier. Reduce the number of variables going on here.

---

just saw your new post which seems to invalidate measurements in post 30 and Q752 is showing properly behavior as the difference between E and C is what it should be - around 4 volts and not 25V... At 25V this would cause your driver transistors to get hot and fry. Please ensure R752 is intact in any case and hopefully not flaky, but if your new measurement is correct then R752 is working.

Again failure in QN01-QN03 will not cause your driver transistors to get hot, these merely cause shutdown to protect your speakers.

[hyva_ana]

Re: Marantz PM-66SE Burns Transistors

if E-Q752=-25.6V and C-Q752=26V to 10V to 0V, this transistor is not working properly. If the transistor is working and not getting hot, this would imply R752 is broken.

However I'm worried about measurement errors as the numbers reported post 35 are different in post 30 for Q702.

I do apologize for all helping, we sometimes ask people to do things over and over again whether by mistake or TLDR, but sometimes this does show some measurement errors and without accurate measurement we can't deduce what's wrong.

When I said input shorting, I meant the inputs to the entire amplifier - just want to make sure you didn't have some signal, especially one with a DC offset, going into the amplifier. Reduce the number of variables going on here.

---

just saw your new post which seems to invalidate measurements in post 30 and Q752 is showing properly behavior as the difference between E and C is what it should be - around 4 volts and not 25V... At 25V this would cause your driver transistors to get hot and fry. Please ensure R752 is intact in any case and hopefully not flaky, but if your new measurement is correct then R752 is working.

Again failure in QN01-QN03 will not cause your driver transistors to get hot, these merely cause shutdown to protect your speakers.

Only thing that goes to the amplifier board is that three pole transformer cable. Nothing else.

Q752 stays cool as well as R752 and it is very good looking, like a new and reads 10 kohm.


As I have told before, there is something "going on" on that board. Sometimes voltages are steady and stable, sometimes some voltages fluctuates all over the place and so on...

[eccerr0r]

Re: Marantz PM-66SE Burns Transistors

Do you have clips for your meter, perhaps what's next is to clip to specific points and carefully try to flex the board to see if voltages changes upon slight bending.

If this ends up being a problem, then it's up to you to figure whether this is worth to fix or not.