Philips PM3335/40 scope startup problems

[Stein-Olav Lund]

We have a Philips PM3335 combiscope which has begun to get startup
problems, the LCD shows all characters, and CRT is blank (seems like a
uController not initialized)
When the scope is switched off and in fast sequence switched on again,
it most often comes up. I have looked at several signals to the uP
(8032AH) especially the RESET line, but I can't see anything obvious.
We don't have a service manual for the scope
Any tips are welcome.

Stein-Olav Lund
Trondheim, Norway
Service engineer

 

[Asimov]

"Stein-Olav Lund" bravely wrote to "All" (06 Oct 03 12:23:43)
--- on the heady topic of "Philips PM3335/40 scope startup problems"

It may be a problem with the LCD display communicating with the uP and
nothing wrong with the reset. But the idea may just be a case of
killing the messenger. If you strongly suspect the reset line then
trace it and replace any dry or leaky electro used for timing you may
find. Perhaps a switching diode is associated with the reset cap and
diodes sometimes do go intermittant open circuit. Does mechanical force
seem to affect the failure to start up? Perhaps a cold solder joint in
an area that gets a lot of heat cycling like in the power supply?

SL> From: Stein-Olav Lund <stein.o.lund@iet.hist.no>

SL> We have a Philips PM3335 combiscope which has begun to get startup
SL> problems, the LCD shows all characters, and CRT is blank (seems like a
SL> uController not initialized)
SL> When the scope is switched off and in fast sequence switched on again,
SL> it most often comes up. I have looked at several signals to the uP
SL> (8032AH) especially the RESET line, but I can't see anything obvious.
SL> We don't have a service manual for the scope
SL> Any tips are welcome.

SL> Stein-Olav Lund
SL> Trondheim, Norway
SL> Service engineer


.... High voltage can give a dangerously uncomfortable discharge.

 

[Stein-Olav Lund]

Asimov wrote:

"Stein-Olav Lund" bravely wrote to "All" (06 Oct 03 12:23:43)
--- on the heady topic of "Philips PM3335/40 scope startup problems"

It may be a problem with the LCD display communicating with the uP and
nothing wrong with the reset. But the idea may just be a case of
killing the messenger. If you strongly suspect the reset line then
trace it and replace any dry or leaky electro used for timing you may
find. Perhaps a switching diode is associated with the reset cap and
diodes sometimes do go intermittant open circuit. Does mechanical force
seem to affect the failure to start up? Perhaps a cold solder joint in
an area that gets a lot of heat cycling like in the power supply?

SL> From: Stein-Olav Lund <stein.o.lund@iet.hist.no

SL> We have a Philips PM3335 combiscope which has begun to get startup
SL> problems, the LCD shows all characters, and CRT is blank (seems like a
SL> uController not initialized)
SL> When the scope is switched off and in fast sequence switched on again,
SL> it most often comes up. I have looked at several signals to the uP
SL> (8032AH) especially the RESET line, but I can't see anything obvious.
SL> We don't have a service manual for the scope
SL> Any tips are welcome.

SL> Stein-Olav Lund
SL> Trondheim, Norway
SL> Service engineer


... High voltage can give a dangerously uncomfortable discharge.

The problem was burnt RS232 drivers _AND_ the UART in the scope.

The 5V was a little low due to this (around4.6V)

Stein