Temperature Q4 transistor 2SB531 TRS-80 M1

[HansTRS]

Currently I am restoring a TRS-80 M1 with Japanese PCB and I have now replaced all electrolytic capacitors. The RAM chips have been checked and replaced if necessary. On the RAM IC sockets I measure the correct voltage approximately -5V, +5V and +12V. So far so good.

But transistor Q4 (2SB531) does get very hot, I measure about 75 °C / 167 °F. I know it can get hot (see other post) but can anyone tell me if this very high temperature is normal?

 

[Trash-Eighty]

This high temperature isn't normal. In Adrian's video the reason (fault) for this is explained and a solution is provided.

 

[HansTRS]

Thanks for your advice! I just watched the video, but if I'm not mistaken (English is not my native language), transistor Q4, which is the TO-3 housing, remains very hot when Fabian closes the power supply section in the video.

Am I mistaken?

 

[Trash-Eighty]

You are right. I had mixed up Q4 and Q3.
Therefore a temperature of 75°C is normal for the Q4. This transistor has the big heat sink for that reason. So it's fine with that.

 

[HansTRS]

That's nice to read, then I no longer worry about this high temperature. Thanks!