hg_man
Well-known member
Situation: I inherited a Soundcraftsmen MA5002 power amp. One channel (the B channel) has gotten increasingly distorted.
On the scope, the B channel can be seen to be clipping on the negative peak of the wave.
The B channel's heat sink, while not overheating, is substantially warmer than the heat sink of the A channel under the same load. This leads me to suspect one or more of the 4 transistors on that heat sink.
I got the schemo and service manual and parts list. This let me narrow down the search to one of three transistors. Unfortunately the manufacturer used transistors just labeled "#4 power". I expect that these were simply commercial transistors that they relabeled. (I looked carefully at the transistor case, to no avail - I expect they used solvents to remove the original numbers.)
So finally the question: is there any way I can make an educated guess as to what to replace these with? I expected to see a lot of NPN transistors in TO-3 packages, but so far I haven't found very many.
Thanks for your help.
On the scope, the B channel can be seen to be clipping on the negative peak of the wave.
The B channel's heat sink, while not overheating, is substantially warmer than the heat sink of the A channel under the same load. This leads me to suspect one or more of the 4 transistors on that heat sink.
I got the schemo and service manual and parts list. This let me narrow down the search to one of three transistors. Unfortunately the manufacturer used transistors just labeled "#4 power". I expect that these were simply commercial transistors that they relabeled. (I looked carefully at the transistor case, to no avail - I expect they used solvents to remove the original numbers.)
So finally the question: is there any way I can make an educated guess as to what to replace these with? I expected to see a lot of NPN transistors in TO-3 packages, but so far I haven't found very many.
Thanks for your help.