# PPI Pro MOS 50 - Identify this component



## TomV (Nov 17, 2020)

*[Background]*
I'm the original owner of 3 Precision Power amplifiers from the mid 90's. (PPI 2050AM, PPI 2150AM and Pro MOS 50) These amps were retired form use in 2000 and stored in a bedroom closest. 

Now a blast from the past and 20 years later, I plan to use them in my 1989 Mustang GT, as they will be "period correct" and didn't have any problems when stored.

Before I reuse them, I plan to solder in new electrolytic capacitors as we all know they degrade over time. In fact, I just spent $50 from Mouser Electronics to recap all 3 amps.

*[Issue]*
While determining what capacitors I needed, I noticed one of the Pro MOS 50 components appears damaged. It almost appears to have been damaged by a soldering iron during original assembly, but I'm not certain. I don't believe it's non-functional, but while I'm doing the capacitors I could easily replace it. The problem is I don't know what it is?










See the attached pictures of component TS1. I believe it might be a TVS diode or type of rectifier that is unique for lthe ow impedance protection of the Pro MOS amplifiers. The 2150AM doesn't use the same components, but it does have a TS1, TS2 and TS3 on the same locations of the printed circuit board. Any input would be greatly appreciated.


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## TomV (Nov 17, 2020)

I've been searching for more details and leaning towards the ProMOS50 having a Thermal Switch (TS1) that opens the circuit when too hot and closes after cool down. I wonder if PPI quality control tested it with a soldering iron? I suppose I could check continuity and heat it to see if it opens.

The PPI 2150 appears to have 3 Temperature Sensors (TS1, TS2, TS3) and yellow protection LED. This is probably an earlier design of thermal detection using 3 thermistors, but I'm not sure how the test circuit works to protect the amp.


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## SQ_Bronco (Jul 31, 2005)

I think you are correct. I am on the road but iirc on my promos50 it also looks damaged but the amp works fine. Its been years but I think I actually considered fixing it in the past and decided against it. I’ll be back this weekend and try to remember to take a look. I have a 2150m as well I can compare it to.

I seem to recall that Perry Babin specifically talked about this part in his amp repair tutorial.


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## TomV (Nov 17, 2020)

Thanks for the reply. I also found a picture of another promos50 on eBay and it looks the same.


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