A Hallelujah moment

[62vauxhall]

The past few weeks I've been picking away at trouble shooting a free NAD 7225pe receiver, using the primitive means at my disposal. I have been pulling transistors to check them and suspected that two I removed were actually installed backwards. It was very time consuming (for me anyway), following the schematic to determine which pin went where.

Untill today.

I discovered that the service manual for this receiver was not as informative as that for it's 3225pe integrated amp counterpart.

After spending a whole bunch of time in this process, I just realized what this symbol means for TO220 transistors.

 

[J!m]

They sometimes have them listed off to the side on the schematic with part number and pin out. Not always, but Kenwood, Pioneer and Micro seem to do it.

 

[WOPL Sniffer]

If the amp has been worked on/upgraded beware, the 220's can go in either way. On the Carver M1.0's M1.5's etc.... we install newer transistors which may or may not have the same pin out so we have to flip them. So, you COULD have a transistor which you may think is in backwards but may NOT be.

 

[62vauxhall]

Yes and two of them are supposed to be 180 degrees from the corresponding two in the other channel. Seeing that some were installed one way and some the other made me wonder about orientation of the lot of them.

The integrated amp's service manual, but not the receiver's, had diagrams of the trace sides of the board that included those symbols and transistor position numbers. Studying that clued me in. I realized then that the circuit board actually did have that symbol for each TO220 and that some were the reverse of others.

If I had known that before it would have saved me a lot of time determining what component the emitters connected to so I could confirm transistors were right way round or backwards.