Need a hand understanding how to read a part of the schematic.
So, as reported in the earlier thread, after repairing the KMA-01 hybrid IC on the PSU, the scope came to life without any issues other than calibration.
There were two of these scopes in the job-lot however, and the 2nd one also had the same bad IC on the PSU which was repaired in the same manner. This 2nd scope also had some missing transistors on the main board, which only arrived yesterday, and unfortunately, installing these components hasn't helped to resolve the lack of trace on the CRT. I know the CRT is working as it was tested on the other 'good' scope.
All of the LV rails are also present and correct at the input connector to the main board, so the PSU is sound.
The area on the main board in question, is part of the CRT control and via VR104, regulates two +37.5v lines which are taken from the +80v rail. At the moment the Collectors are reading 77v on one rail (Q's 14+15), and 5v on the other (Q's 12+13). Not 37.5v.
What I am not yet understanding, is the sequence of control signals (or where they ultimately come from) to the bases of the transistors which regulate the +37.5v lines.
There is the +80v input as well as both +8v and -8v connections further down the circuit.
For comparison, I've taken voltage measurements from both scopes and it is clear that the 2nd scope is at least a couple of sandwiches short of a picnic.
The section in question is attached if anyone fancies a challenge?
I'll post photos and all the voltages if it will help
So, as reported in the earlier thread, after repairing the KMA-01 hybrid IC on the PSU, the scope came to life without any issues other than calibration.
There were two of these scopes in the job-lot however, and the 2nd one also had the same bad IC on the PSU which was repaired in the same manner. This 2nd scope also had some missing transistors on the main board, which only arrived yesterday, and unfortunately, installing these components hasn't helped to resolve the lack of trace on the CRT. I know the CRT is working as it was tested on the other 'good' scope.
All of the LV rails are also present and correct at the input connector to the main board, so the PSU is sound.
The area on the main board in question, is part of the CRT control and via VR104, regulates two +37.5v lines which are taken from the +80v rail. At the moment the Collectors are reading 77v on one rail (Q's 14+15), and 5v on the other (Q's 12+13). Not 37.5v.
What I am not yet understanding, is the sequence of control signals (or where they ultimately come from) to the bases of the transistors which regulate the +37.5v lines.
There is the +80v input as well as both +8v and -8v connections further down the circuit.
For comparison, I've taken voltage measurements from both scopes and it is clear that the 2nd scope is at least a couple of sandwiches short of a picnic.
The section in question is attached if anyone fancies a challenge?
I'll post photos and all the voltages if it will help
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