Philips PM2527

[Zeitkind]

While trying to repair a Datron multimeter, my good old Philips PM2527 multimeter started to fail… grrreat timing.    Yes, it's an old meter, but I like it.
Symptoms: DC Volt in automatic range showed eg. 10V (correct), manual mode showed ~4,98V (wrong, always about 50%). Also, the decimal point jumped around. After switching ranges and modes around the DC volt mode is often completely out of order, all I see is a "00", which is out of range.
But: If I power off and power on again, it may work again without a problem - or may not. Ohms seem to work fine, but I haven't tested this in deep.
Anyone seen this before? The unit was never serviced, so prob. a recap? The service manual lists ~26 electrolytics, but I haven't look inside yet.

[SingedFingers]

I have a PM2524. It's the range switches that went dicky on mine. If you can get into it (the PM2524 is a bastard to get inside) and expose the range switches, pull the little plastic caps off the end if present and spray some decent quality contact cleaner and stab at the switches heavily a few times. Cured mine.

Haven't checked the schematic but there's usually a mains isolation transformer followed by a small switching supply. Check the voltages and ripple on the output of the switcher with a scope as well.

I actually did this on mine only the other day. Details here: http://vintage-radio.net/forum/showthread.php?t=133612

The electrolytics are all fine in mine and mine was made 34 years ago. It's a very good meter!

[Zeitkind]

Update: Well, it's always the electrolytics? Not sure yet, but almost _every_ small cap is either totally dead of way out of spec. All 3,3µF are more of less open circuit with capacitance below 50pF. And there are many inside.. The unit is terrible to disassemble, it's a mess, and many plactic-whatever-things-to-hold-the-PCB are broken (aged). Not sure yet how to replace them. I will try to fix it, but Jesus, that's a terrible meter inside..  Gonna have to use a big pile of hot glue..

[SingedFingers]

Good luck. I'd probably scrap it or strip out the expensive parts (ICs, FETs and 0.1% resistors) if it was in that state.

The big plastic spacers that clip onto the board only break if it's dropped. One of mine is broken after the idiot who shipped it did it with the handle extended. Still holds together though.

[Zeitkind]

I won't buy new axial caps for it. But I have enough spare radial 3,3µF caps and others to replace all. So, well, I will try to repair it. The biggest problem are those broken plastic sliders that hold the PCB and are screwed to the shielding on both sides. They just brittle in your hands and quit their job while I took the meter apart. I need a non-conductive replacement that is strong enough, which is.. hmm.. no idea. It might end up with a messy bunch of hot glue..
It's always the same with old equipment. You got used to it and will miss it though you know for sure it's not really worth repairing. A new shiny plastic meter from Uni-T, Mastech or $brandname will be as precise as this old Philips and won't cost my time and money.

[SingedFingers]

Are those the clear plastic ones? If so I thought about replacing them with M3 studding and a mix of rubber and metal washers and nuts. I've done this on equipment I have designed to perform the same task.

All my kit is now older than 1994 - it's fun fixing stuff

I really don't trust some of the newer cheap ass meters. They have virtually no protection. The Uni-T UT61E I had was scary; got rid of it. The PM2524 isn't very good either to be honest but it's a 4.5 digit meter so it's staying until I pick up a cheap Fluke 8050/8060 on ebay

[Zeitkind]

Are those the clear plastic ones?

Hard to describe.. The PCB is surrounded by 2 metal shields on the left and right. These shields are screwed to the left and right aluminium chassis. But not directly, the nuts sat in several sliding plastic pieces - and those are completely gone. Not sure why they took plastic, I could take some metal <whatever>, but not sure if the electrical contact to the outer chassis would be a wise thing to do. Simply solder the nuts onto some metal pieces might be the easiest way, need to check, if there is electrical contact by design anywhere else. If both are isolated, I have to find some stiff plastic, wood or <whatever>.