SR-52A rebuild project (SR-52A 942058 LTA4176)

[albertofenini]

Thank you very much
However, the SR-52 troubleshooting guide never mention a Q4,
it mentions a Q1, a Q2 and a Q3
I need to go back to the PCBs and take a good picture
On the other side, I don't remember removing a Q4 and the holes on the PCB look really untampered
Do you mean that if Q1 and Q2 are present, then Q3 and Q4 are not necessary ?
Please bear in mind that on both spare units Q3 is indeed present
Thanks again for help
If you have any picture that would be of help
In the pictures provided by another firm member, in order to reconnect the card reader, I can spot a Q4 ...

(03-05-2021 03:33 PM)jebem Wrote:  Q4 is used with Q3 as a Darlington pair to drive the motor on the original SR-52 model PCB.
Q1 and Q2 are used as the Darlington pair to drive the motor on the SR-52A revisions.

Q4 do not have special requirements in this position, any npn high current type is adequate, see the Q2 specs on the SR-52A revision, it should be similar.
I would say a npn with IC of 1 ampere maximum and VCE of 20 volt would do the job.