debugging a TSSA 1.8

[sonnya]

Yes it need to be powered. anything between +/-18V to +/-32V is good.

 

[Siberia]

Q8 identified as the problem. The v1.7 schematics indicates part number PMBFJ175. Obsolete. @sonnya can you confirm it's the same part on v1.8? And what could be the replacement?

 

[sonnya]

Here it is in stock

https://www.digikey.dk/da/products/detail/onsemi/MMBFJ175LT1G/919588

 

[Siberia]

Thank you. Local shop also indicates as possible to obtain. Waiting for their answer.

 

[sonnya]

I would post all my files on the tssa v1.8.

Pads viewer can be used to follow traces and read diagrams.

 

[Siberia]

yes, please do

 

[Siberia]

Still struggling with it. Replaced Q8 and now the board takes power alright. No hectic behaviour as previously.
Now the offset is 40mV and the pot is doing nothing to it. Same for bias – 0V and not reacting to bias adjusting.

 

[vgeorge]

Measure pot resistance. Sometimes multiturn trimmers fail.

 

[Siberia]

Just checked them. And they look like they respond to manipulations.

 

[Siberia]

@sonnya Do you have voltage schematics to share, so I could check around the circuit?

 

[Siberia]

Do I have any other troubleshooting options without buying a SG and a scope?

 

[sonnya]

No I do not have a voltage schematic.. Sorry.

But on gate of each mosfet you should have around 1.2V and 1.6V ... they are asymmetrical.

BR

Sonny

 

[Siberia]

I have v1.8 amp and v1.7 schematics. Is it much different?

 

[sonnya]

Only one capacitor in difference. The yellow ceramic capacitor close to ECW20N20 or 16N16

 

[vgeorge]

Once again one channel stopped working. This time it was one of the L1 or L2 that was desoldered. Put some extra solder for safety to both of them and the amp is back to normal.