Sansui AU-6900 Posistor destroyed

[CJDJ]

Re-assembled my Sansui AU-6900 and forgot to re-attach posistor to heatsink.
Turned on amp and it blew 2 fuses straight away.
1. Could not attaching posistor be the cause of blown fuses?
2. I also need to find a replacement posistor as I've accidentally destroyed mine in meantime (don't ask). Any idea what value it is?

Posistor is pictured attached to heatsink (not my actual amp but same thing).

All it says in service manual is 'posistor', part no. 0320120.

Any advice gratefully received.

 

[ivandezande]

1: No. You messed up somewhere else. Why aren't you using a DBT?
2: Not sure. eBay is your friend.

 

[GrisPato]

https://audiokarma.org/forums/index.php?threads/need-help-pth487a-posistor.61799/

In this thread you can find the info you need.

 

[Hyperion]

https://audiokarma.org/forums/index...0000-protect-mode.914226/page-2#post-14041759

This thread might also be of interest.

Unfortunately one thread that is referenced by me and others as a Golden source of information for this issue is no longer accessible.

 

[CJDJ]

Thanks for the advice. The Murata PTFM series look like a perfect replacement but no longer manufactured.
Still not sure what resistance value to use for the AU-6900. Found some 2.2K ones on eBay so might try them.
The posistor is on the power amp board 2596 (PR601), but can't find it shown on the schematic.
Murata PTFL series is a leaded blob type rather than metal ring terminal so might work but not sure how to mount it on heatsink. Maybe glue it in original ring terminal with hot glue?

 

[CJDJ]

1: No. You messed up somewhere else. Why aren't you using a DBT?
Thanks yes, assumed it was probably another issue causing fuse blow. Maybe time to make a DBT.

 

[richardpp]

Thanks for the advice. The Murata PTFM series look like a perfect replacement but no longer manufactured.
Still not sure what resistance value to use for the AU-6900. Found some 2.2K ones on eBay so might try them.
The posistor is on the power amp board 2599, but can't find it shown on the schematic.
Murata PTFL series is a leaded blob type rather than metal ring terminal so might work but not sure how to mount it on heatsink. Maybe glue it in original ring terminal with hot glue?

Try looking for a replacement with a resistance value of around 200 -300 Ω at 25°C. 2.2KΩ is way too high and will likely put the amp into protection. It’s also important to have the eyelet connection for good thermal bond.

This could be an option: PTC (Positive Temperature Coefficient) p/n: B59052D1070A040
It has a target temperature of 70°C and a resistance value of 570Ω (still okay) at 25°C, operating voltage 30V.

BTW, the posistor is identified as PR601 on F2596.

 

[CJDJ]

Great advice thanks. Somehow missed the Epcos TDK ones at Mouser and appreciate your guidance on values. Will put on my next Mouser order and report back. Thanks for showing the PR601 on schematic. It was eluding me.