SX-750 Bulb Trouble

[theiceberg]

OK, I finally got the reading for the four drivers, don't have the pin numbers so just made a template for them, orientation is as would be looking at the back of the machine. In regards to the transistors, I ended up going with these NSC 2SB541/2SD388 set, I'm thinking these will work?

 

[Watthour]

I don't understand your readings. The common method for testing bipolar transistors is to measure forward and reverse junction voltage drop for each of the three junctions. This is colloqially termed the "six-way diode test" detailed here: https://www.audiokarma.org/forums/i...lar-junction-transistor-testing-basics.43186/

TO-3 case devices (your output transistors) commonly have their connections as follows:

Set your meter on a diode test range, usually denoted by a symbol like this. ─►|─ The meter display should indicate the voltage drop across the junction being measured. That is the critical data we need to determine the potential health of the output transistors (or any other bipolar transistor, for that matter).

 

[theiceberg]

I see, my mistake. I'll retest these and report back.

 

[theiceberg]

Oh, to note, I posted data for the housing components wired to the power supply, and labeled voltage from each colored wire as such. The transistors were measured in this way you posted, 2 were indicating failure, reporting inconsistent values when compared to the other same model transistor.

 

[theiceberg]

So, the news was going to be moderately positive, but now its not looking too good. Received the transistors, and did a quick install and test to check their behavior. No more protection circuit activation with both bookshelf speakers on, but the problem persisted with the one speaker, very quiet and with raised volume, horrible sound quality. So I proceeded to screw everything back down and retested to see if there were contact issues. Isolated the problem speaker via balance, turned up volume, protection circuit activates. In addition, one of the covered resistors on the 046 board burns and smokes. A picture was taken of the original transistors, and the new ones were installed using that as a guide, and they only go in one way, so I am hesitant to blame this. I will wait to proceed until a bit more concrete advice may be given.

 

[theiceberg]

Alright, to anyone getting to this point of the thread, I think I'm calling it here. The bulb issue has been resolved, and I'm getting into irrelevant territory now in this thread. I will make a new post outlining the new issues to keep it more accurate. Thanks everybody for the help getting to this point!