Well that was the easy bit with the HP 5248M, one dead 1853-0001 transistor (Q3) on the A25 oscillator power supply board replaced, luckily I had a used spare from something else. Output now back to +20V with a load test and I reconnected/refitted it to the counter.
Apparently 1853-0001 is a selected 2N1132 (according to the 5065A manual) and 1854-0003 on the same board is a selected 2N1711, if that helps anyone else who needs to replace those.
![](https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/?action=dlattach;attach=1117422)
![](https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/?action=dlattach;attach=1117426)
Still lots more problems to find & fix with this counter, at least it now has a 5MHz & 10MHz output on the back from the 00105 series crystal oven, none of the other selections or the separate 100MHz output are working.
The main input board & six out of the eight display boards are working properly, but it currently only counts in manual count mode with the gate active all the time.
David