Marantz PM32 help

[Honda Z50M]

I've just picked up a faulty Marantz PM32, it was used to drive speakers with too low an impedance, which shafted it.

IF any of you guys/dolls could give me an idea of a anything to check so I can repair it it would be appreciated.

Thanks in advance

Tom

 

[dragonweed]

What is your knowledge/experience/confidence level on the subject?

 

[Honda Z50M]

I would say not bad, excellent soldering skills, reasonable fault finding etc

 

[dragonweed]

Check the parts circled on the picture (most likely candidates in the event of failure you described), also for blown fuses (if any), burned, discolored resistors, bulged, leaking electrolytics, darkened PC board areas, signs of overheating, etc.- the usual stuff.

 

[Honda Z50M]

Thanks, won't be able to look until Monday (amp is at work)

Do oyu know if the compenents are still available or possibly better alternatives?

I guess if one blown the same componenets for both channels will need replacing.

Tom

 

[Honda Z50M]

Initial power up 1A fuse at switch blows.
Doesn't blow when power disconnected from PCB.
Transformer output measures 28.9v 0v 28.9v
Short across pins 2and3 of Q761 (D1894) and Q763 (B1254)
Resistors R805 and R806 appear to be open circuit (PCB around both slightly darkened)

Tom

 

[dragonweed]

Usual symptoms of a blown OP stage.... The outputs are Darlington types, so you need the originals to replace them. R805 nad 806 are in the supply circuit for the protection IC (QN 04 - TA 7317), so it might failed too, but this is not a common failure, so check around what else could have gone wrong in that vicinity. Mains fuse should be 1.6A, not 1A. Also check Q751, 752, Q703, 704, QN 01, 02, 03, Q 801, Q802. In some cases the driver IC (Q 705- AN7062) also blows, but it is not easy to measure. When you replaced everything suspect, power up the amp with the "light bulb in series with the primary" method, so it won't blow everything again.
Good luck!......

 

[Honda Z50M]

Thanks for the reply.
I take it I can remove Q's 761 and 763 and power up (should I fix other issues in PSU side of things.)

Tom

 

[dragonweed]

Not sure it is a healthy idea to power up the amp without the output transistors....

 

[dragonweed]

The driver IC will be open loop, DC levels might shift, etc., dozens of things can go wrong......

 

[Honda Z50M]

Do you know if there is much difference in alternative transistors and originals (B1254/S2B1254 and D1894/S2D1894)?

Tom

 

[dragonweed]

B1254=2SB1254, D1894=2SD1894. There are no such transistor types as S2B, or S2D...... If you cannot get the originals you can substitute them with TIP142/TIP147 pair- lower voltage (still OK), higher current, higher power dissipation, and a bit slower than the originals.

 

[Honda Z50M]

That's probably what I meant sorry..