Hello,

I have a secret service pinball machine and I am getting a strange reading on the power supply for the alphanumeric display.

The voltages I see for the display are the following:

+102.8 vdc
- 122.9 vdc
+ 4.94 vdc

The negative voltage for the display seems really high. I have verified the components in the circuit for the negative voltage and they all test normal.

Anyone ever had this issue?

TR4 has a mds60 installed instead of a MJE350.

the mds60 appears to be factory installed

it reads 122 with and without the display attached

TR4 is the transistor in question.

looks factory installed which is strange they would install a mds60 instead of MJE350

P1040276.JPG

desoldered the mds60 and ordered parts from GPE.

will update what changes this makes.

still no idea why the mds60 was there

tested everything else and its all normal. the zener diodes are 4763a so someone swapped them already.

the only thing which doesn't test correctly is the mds60. so hopefully when I put the MJE in the voltages drops to the correct level.

thanks,

I am seeing 99.8v and -105.6v on the zener diodes

I actually just ordered a MJE15035 from your site which is what the schematic shows. I know I will have to bend the pins but is there any downside to using this part instead?

installed the MJE15035, had to bend the legs as different pinout.

the voltages now read at the display!

99.8vdc and
-105.6v

I will be replacing all of the resistors soon so that should drop both down to 90vdc

thanks all!