Philips PM2534 - Test EPROM

[meandeev]

Hello,

does anybody has a test Eprom (or an image), that is mentioned in the service manual?
I´m looking also for an image of the normal eprom.

I´ve got this multimeter. It is in strange condition. Some measurments are ok, some not, cannot be calibrated...
I know, it is not the best thing, but it was cheap and I want to learn, how these things where build 20+y ago.

Thanks in advance

[Smith]

It doesn't care if it's cheap or expensive, if it does the job for you, then it's fine. I've got some old Philips stuff from the same era, and the quality is quite good. Some cheap stuff too, but it serves me well.

Don't these things have batteries inside? Have you checked these? When batteries go flat, the strangest of things can (and therefore will) happen. Check and replace them if needed, then try calibrating again.

[therew]

Hi looking for the service manual of this system voltmeter or if anyone can provide the technical specs it will help as well.

[PA0PBZ]

Hi looking for the service manual of this system voltmeter or if anyone can provide the technical specs it will help as well.

http://www.ko4bb.com/manuals/download.php?file=Philips/Philips_PM2534_PM2535_System_Multimeter_Service_Manual.pdf

[meandeev]

@smith: if my post sounds a little bit negative - this was not my intention. I´m fascinated which precision was achieved. I used these kind of multimeters when I was a student - but is was strictly forbidden to open it. 
 
I replaced the battery - this was the first thing that was done. I did it while it was powered with 2 alkaline cells and a resistor. Nevertheless after that I saw "NC" while calibration sometimes - so I followed the procedure that should be done after RAM replacement.  But even after that I saw (sometimes!) "calibration fail"

@therew: I found only 3 "different" links, but it seems, that all came from the same source (scan). The link that was posted by paopbz is one of the better quality documents.

One can find my "normal'" ROM in the attachment

[Smith]

Calibration failure can mean several things.
1. A value which is out of bounds (probably a hw failure or dirty connections/PCB or a measurement error.
2. Device is not in calibration mode. Some devices need to be unlocked by hw or sw.
3. Unable to save the new cal value. This is quite unlikely.

Number one seems the most probable (taken into account you followed the manual). Which measurements work, and which don't? Are they far out of spec?

[meandeev]

I agree with you for the possible problems. I can reject no.2 :-) I followed the service manual. So no.1 and no. 3 are on the table. I asked for the test eeprom to eliminate no. 3.

My plan was eliminate no.3 - and then dive into the schematics. I sent the device to a calibration company and got an income protocol, so I know what was in the specs. So some values were marked as "failed" even there was a "more or less nearby value".
For instance: resistance 2wire faulted. If I connect a 3.00.. Kohm value (measured with a keithley 196) then it shows 2.8... Kohm. I couldn´t  calibrate this for sure (sometimes it was possible, sometimes not - got "fail" - I tried it several times)

How stable should the resistor be? Maybe It´s the temperature drift of the test 3k-resistor (2 trimmer resistors)...

[Smith]

Temp drift should be less than 1000ppm for the worst trimmers, that would need to be (200E of 3k) 6,7% dev /0.1 = 67 degrees drift minimal. So that's not the issue.

Normal metal film resistors would do fine for most diy calibrations unless you go 5.5 digit and up. Compare it to your 196 in the same room, and temp drift should not be an issue.

How is your current measurement? If this is off too (at least the mA range and down) my first bet would be on moisture or contamination on the PCB. If other ranges deviate too, then check voltages first.