Tektronix PS280 troubleshooting - problem with channel outpu

[nad5273]

Hi everybody,

I have a Tektronix PS280 power supply, but i am looking for help to
troubleshoot it.

Here is the problem: channel 2 outputs a high voltage, around 42-44V
(This is very disturbing since the PS280 is rated to output 0 to 30V).

I am an electronic student, have the required equipment to repair this,
but i don't have any clues about how to tackle this problem. If anyone
can give me cues about what to verify, what could be wrong, i will
greatly appreciate it.

Thanks a lot, hope to have help !

Nadine

 

[BobH]

nad5273 wrote:

Hi everybody,

I have a Tektronix PS280 power supply, but i am looking for help to
troubleshoot it.

Here is the problem: channel 2 outputs a high voltage, around 42-44V
(This is very disturbing since the PS280 is rated to output 0 to 30V).

I am an electronic student, have the required equipment to repair this,
but i don't have any clues about how to tackle this problem. If anyone
can give me cues about what to verify, what could be wrong, i will
greatly appreciate it.

Thanks a lot, hope to have help !

Nadine

Hi,
The first thing I would recommend is to find the service manual on it. I
looked at the best place I know of (other than Tek) for manuals and
didn't see it. Tek had a users manual on the web site, but they wanted
me to register, so I skipped it.

Without a manual, it takes either luck or a lot more work. I am assuming
it is a linear regulated supply, as that is what most variable benchtop
power supplies are. The output being stuck at a high voltage may be a
shorted series pass transistor. If you look on the back of the supply,
the pass transistors will probably be on the case or a heat sink, as
they can produce quite a bit of heat (44V - Vout) * Iout watts or so.

If the part is socketed, pull the transistor and check for a collector -
emitter short with a meter. If it is not socketed I would unsolder the
transistor and do the same test.

Good Luck,
Bob