Marantz PM-7200 Front Panel IC

Following the tracks on the board, Pin 18 goes to the emitter of a TO-92, out of the collector and into the negative side of an electrolytic 50v 22uF. I'll test it in the multimeter to see if it's still alive.

Interesting... The amplifier I repaired also had a TO-92-like transistor in its microcontroller reset circuit and it was actually the transistor that had broken down - I remember because it seemed so unusual. I don't think it was a Marantz, though.
 
Interesting... The amplifier I repaired also had a TO-92-like transistor in its microcontroller reset circuit and it was actually the transistor that had broken down - I remember because it seemed so unusual. I don't think it was a Marantz, though.

Yep, it turned out that it was a faulty TO-92 as well: marantz PM7200 dead
 
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The most simplest way to test a crystal and I used to test communications crystals when younger is to monitor a signal generator with a ,scope --put the crystal in series and watch for a much increased resonance while tuning the generator.


Yes I know you can buy --xyz or use sophisticated gear but that used to work for me.


I would be interested to know what your next step is now ?
 
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I’d be very careful not to blame the controller until being absolutely sure it wasn’t the clock, reset ( if external) or PSU.

They are incredibly reliable and almost always only go if abused.

I haven't followed the thread but absolutely agree 100% on this...

I always (always :)) used to go around every pin on a suspect uP with the scope and make sure that what you saw looked reasonable.

If there are any 'keyscan matrices' then make sure no buttons or diodes in the matrix are leaky.

Its never the big chip ;)
 
I've also tried bypassing the TO-92, wiring pin 18 straight to VDD but still nothing.

Pin 18 is an active-low reset with built-in pull-up resistor, if I understood the datasheets, so with pin 18 hardwired to the supply, the microcontroller doesn't get reset properly. You could disconnect it from the external circuitry that's normally connected to it and give it a 4.7 uF or so capacitor to ground.
 
The most simplest way to test a crystal and I used to test communications crystals when younger is to monitor a signal generator with a ,scope --put the crystal in series and watch for a much increased resonance while tuning the generator.


Yes I know you can buy --xyz or use sophisticated gear but that used to work for me.


I would be interested to know what your next step is now ?

I haven't followed the thread but absolutely agree 100% on this...

I always (always ) used to go around every pin on a suspect uP with the scope and make sure that what you saw looked reasonable.

If there are any 'keyscan matrices' then make sure no buttons or diodes in the matrix are leaky.

Its never the big chip

Pin 18 is an active-low reset with built-in pull-up resistor, if I understood the datasheets, so with pin 18 hardwired to the supply, the microcontroller doesn't get reset properly. You could disconnect it from the external circuitry that's normally connected to it and give it a 4.7 uF or so capacitor to ground.

Thanks guys, you're all awesome. It's getting close to a point where I'm spending good money after bad but there is a huge row of TO-92s, all of the same value I could try replacing and I have 5 Panasonic 22uF 50V to replace the remaining caps. I'll also try MarcelvdG's suggestion of clipping pin 18 and wiring it to GND via a cap.
 
I was bored this morning so took my working PM7200 to pieces, removed the front panel control board and transplanted it into the faulty amp. Everything fires OK and since I've done more extensive servicing and re-capping, I've kept it now as my main amp.

I did notice that the board was quite different - it matched the schematic in the service manual. From a look at the S-808 CMOS voltage detector guarding the reset pin on the Toshiba IC on the faulty board, the manufacture date on it is May 2004, so I reckon it's a revised board. They've scaled back the number of components on it. The S-808 is an NPN that seems to read OK on the diode setting of a multimeter but I'm damned if I can find a replacement anyway. I can't find the Vce, Vcb or Veb from the Seiko datasheet. It's driving me nuts.
 
I haven't followed the thread but absolutely agree 100% on this...

I always (always :)) used to go around every pin on a suspect uP with the scope and make sure that what you saw looked reasonable.

If there are any 'keyscan matrices' then make sure no buttons or diodes in the matrix are leaky.

Its never the big chip ;)

Also the IC on the transplanted board was different - a 4-bit Toshiba TMP47C200BN instead of the 8-bit TMP87PH46NG hence it may not have been readable / writable between ICs.
 
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It sounds like there was quite a major production change somewhere during its lifecycle... quite strange for an amplifier really. Maybe there are some clues in the full number and any extra letters and digits signifying different global markets.
 
I have a spare pm7200 amp if anybody needs it? I was given it to fix and it was a dry joint issue on power amp.

Got it running well. I should have stopped here!

Decided to do the the electrolytic and lifted a track on power amp,section. The fuses blew and it went back in the cupboard. If anyone can use it it is in good nick and boxed.

Spares or repair £50.
 
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So does it work if you remove the cap?

If it does and the cap is at zero volts then there might be a bit more to it all than that. Some chips can remain 'locked' in an invalid state for days/weeks even when all voltage is removed. One particular remote control was super prone to this.

Interesting :)
 
So does it work if you remove the cap?

If it does and the cap is at zero volts then there might be a bit more to it all than that. Some chips can remain 'locked' in an invalid state for days/weeks even when all voltage is removed. One particular remote control was super prone to this.

Interesting :)

I've just tried that and it powers on but won't come out of protection mode. The input selector works and it responds to the remote control so surely the IC now isn't at fault :)

When I transplant it into another PM-7200, the fault is identical so it must reside on the front control circuit. The only things that haven't been replaced now are the diodes, an axial inductor and the odd looking axial film caps that look like resistors. A tenner would cover it and I've replaced everything else for pretty cheap so it's worth a shot.