High boost pump works but not on low

[M252]

Hi,

We recently did the annual on our M20K 252 and noticed that the boost pump would only run with the high boost switch on but not the low boost switch:

- Checked the switch and boost pump regulator and found that there is a short on cable #2 from the regulator (the yellow cable is somewhere connected to GND). The short has actually damaged the big transistor on the regulator board (a PMD17K100). 

- Now the challenge comes: where is the short between cable 2 and GND.

-> Anyone who has seen similar issues with the low boost pump?, any hints on how to find the short?

Thanks,

M252

[Mcstealth]

Do you have continuity between ground and the transistor? can the transistor be the short itself?

[M252]

Found the reason why the bipolar transistor on the low boost regulator was killed: The boost pump had signifiant mechanical resistance after 2000h and 25 years of service (well I only used it to prime before engine start) but still... 

I sent it to quality aircraft accessories to get it overhauled.