Philips PM2528

[stcoso]

Hi guys i've recently bought this old but very nice benchtop multimeter for a few bucks. It powers up but some strange and obscure messages appear on the LCD. Playing around with the buttons i'm able to make some of the range relays switch (actually only the current range relays)  but i can't get any measurement...
I know it's a long shot but i think that may worth the effort of repairing it

So... i've opened it and checked the power supply and all seems to be fine...

Any hint?





PS i've never seen anything built like this.. it's a thing of beauty. They've put so much care into designing and bulding this thing 

[markce]

Are you sure it's a Philips PM2528?
I only know that one with LED display...

[PA0PBZ]

Are you sure it's a Philips PM2528?
I only know that one with LED display...

Exactly, I have one at home and it's LED.

[coromonadalix]

thats a nice meter,  but  there a ton of trimpots in there, relays too

some inside look : http://www.gloeidraad.nl/radioforum/index.php?id=146115

[markce]

Yep, lots of trimpots, so you can calibrate it with very simple equipment.
The large HP LED's are very convenient. The meter powers on in an instant. Mine is from 1982. I still use it one on a daiyly basis.

[markce]

The PM2528, if that's what it is, has a serial interface to the display (shift registers). On startup it displays whatever is in the registers, looks a lot like 'ABBA' text on my meter   . On mine it's always the same pattern, but its different on another meter.
I guess your meter does not clear the display, so does not finish initialization. It has a 8031 processor control system with its firmware in old EPROMs. Unless you can measure on the processor bus, and given power supply is ok, I would check clock running end EPROM checksum next.

[markce]

.

[stcoso]

I notice only now the reply ! So i'm gonna take some pictures..


Messing around i've noticed that one of the IC (a uln2003) was inserted in its socket with one leg bent up ... is it normal?

[markce]

Depends which ULN2003 you were looking at. The one on the main board is fully used. The one on the display board is only used partly, lifting one of the unused pins is harmless.

[stcoso]

It's pin1 of the uln2003 on the main board

[markce]

Pin 1 is an input, pin16 is its driver output, which connects to the K1603 relay. The "20mA Ac" and "20mA Dc" ranges will not work with pin 1 disconnected.