EEVblog Electronics Community Forum

Electronics => Beginners => Topic started by: david69 on October 17, 2014, 11:30:46 am

Title: Philips PM2535
Post by: david69 on October 17, 2014, 11:30:46 am

Hi, I would like to ask something about multimeter Philips
PM2535, I tested EPROM, SRAM, battery, its OK, but I can`t
calibrate multimeter, I don`t have null and corect voltage,
0> 6mV, 60V > 58V, at DC in NC mode, is there analog hardware problem? Switches seem right? Thank You for any idea..

Title: Re: Philips PM2535
Post by: david69 on October 17, 2014, 12:50:03 pm

I found broken zener diode in reference circuit for DAC ..

Title: Re: Philips PM2535
Post by: EEVblog on October 17, 2014, 01:06:36 pm

Quote from: david69 on October 17, 2014, 12:50:03 pm

I found broken zener diode in reference circuit for DAC ..

That'll do it.
So it's the actual reference zener itself?
In that case it will need careful selection on a replacement.

Title: Re: Philips PM2535
Post by: david69 on October 17, 2014, 05:17:45 pm

Now I have +/-5V reference for DAC, I have short circuit
on input multimeter, but integrator and slope amplifier with comparator still continue generate signal, but I have now smaller value mV on display :( I dont know right function
of multiplexer 4051 with TEST probe clips, I dont have there
any voltage nor signal?

Title: Re: Philips PM2535
Post by: david69 on October 17, 2014, 07:09:20 pm

I removed MUX 4051, and output Z conected to analog ground. Multimeter shows zero in AC modes, 0.19mA,
0.19mV, 0.19Ohm/2W in DC modes, broken power supply??

Title: Re: Philips PM2535
Post by: david69 on October 18, 2014, 01:51:43 pm

I will replace MUX 4051 and switch 4066, +-REF is OK :)
in front of integrator ... power supply is OK

Title: Re: Philips PM2535
Post by: david69 on October 20, 2014, 07:57:56 am

MUX4051 improved DC range voltage :-) but LTC1052
is noise??

Title: Re: Philips PM2535
Post by: david69 on October 21, 2014, 02:10:08 pm

The power analog voltage is +8V, -8V and digital +6V, -6V, There are stabilisators 78L05 and 79L05 with zeners
in collectors, 3V3 and 3V9, and stabistor 1V5. I played
with zeners, and changing voltage has big influence on
measurement, mainly analog voltage, What right value should I have on output power supply?

Title: Re: Philips PM2535
Post by: Simon123 on October 21, 2014, 03:20:50 pm

You mean zeners on ground lead?
The output voltage should be voltage of zener + voltage of regulator.
http://bee.mif.pg.gda.pl/ciasteczkowypotwor/Philips/pm2534_PM2535.pdf (http://bee.mif.pg.gda.pl/ciasteczkowypotwor/Philips/pm2534_PM2535.pdf)
page 66 for psu

Title: Re: Philips PM2535
Post by: david69 on October 21, 2014, 03:48:22 pm

depends on output current and current via collectors
7805 and 7905, there will be difference with types of use zener diodes.

Title: Re: Philips PM2535
Post by: david69 on October 22, 2014, 03:43:29 pm

I have understand PM2535 yet, Calibration DC,AC voltage is OK :-) I think that multimeter is functious :-) AutoZero works
well...

Title: Re: Philips PM2535
Post by: david69 on November 04, 2014, 12:56:50 pm

it is good to replace watchdog 7705, MUX 4051,
switch 4066, chopper LTC1502, zener diodes in power, and capacitors :-)