[SOLVED] Unknown fault transformer in Philips PM 2519

[arkeo]

Hi,

Just today I received a PM 2519 from eBay. Packaging looked good but the multimeter didn't turn on. Once opened I saw that the transformer was uprooted cause an inaccurate transport - but still fixed enough not to make me suspect that something was wrong when I shook the package as I always do.

The wires broke in an area of the transformer inaccessible to the welder so I could not measure the voltage ratio. I tried to open it (it is sealed on one side) to remove a loop both in the primary and the secondary windings and in doing so I interrupted a winding, so I am sure that it's impossible to measure it now. I downloaded the service manual but cannot find where the characteristics of the transformer are declared. There is only the part number for the replacement. I know that it could be possible rebuild a power supply section and supply the voltages required by the circuit (shown in the diagram) but it is beyond my technical capabilities and I would avoid damage the instrument. The only solution I can try for my technical (in)abilities is to replace the transformer but I can do it only if I know the voltage on the secondary. I do not have a variac to power the instrument with a transformer of which I know the data until the instrument turns on. Any ideas?

Thank you very much for any useful information. Sorry for my English, hope it is understandable.

https://www.dropbox.com/s/hzha68oilovw51g/philips_pm2519_service_id517.pdf?dl=0

[Chris56000]

Hi!

The transformer you require has a single secondary winding, 12V rms rated at 1.5A will be adequate to power this meter!

The series regulator is somewhat unusual as it's designed to split the unregulated supply part way to supply +5V & –5V for the various digital and analogue ICs in the meter, but the transformer I suggest will give 18V approx across the 330uF reservoir capacitor C1600.

The series regulator circuit providing the main supplies has built in over–voltage protection provided by the "programmable thyristor" V1603 (BRY39) – failure of the main regulator will result in this device conducting to shut the regulator off.

Two auxiliary supplies of +9V and –9V for the ADC/Amplifier ICs are obtained from V1605/V1606 which is connected as a self–oscillating Hartley oscillator with the centre–tapped inductor T1601 as it's oscillator coil, the +9V and –9V supplies rectified from the outer ends of T1601. A simple voltage feedback loop is connected from the –9V line back to the base/emitter circuit of V1605 to stabilise these two supplies.


You might be able to get a chassis type or a 'block' type pcb mounted transformer that will go in the PCB, failing that, a Chinese 'R' Core transformer with a 12V 1.5A (20VA) transforner will go in there – these have a metal base plate with four mounting holes as standard, and you might be able to redrill the meter chassis to suit the new transformer.

These small R Core transformers usually come with an interwinding screen (green/yellow wire) which should be connected to mains earth/general metalwork of the instrument, and a label is usually provided stating the wiring colours with each transformer.

https://www.ebay.co.uk/itm/20VA-Pure-copper-R-core-transformer-6V-9V-12V-15V-18V-24V-28V-L16-2/192885300377?hash=item2ce8dc1c99%3Am%3Am-WuRptnCwP17Td8HHAKuAQ&LH_BIN=1%7C1

Don't forget to specify '12V' from the "drop–down" selector if you order one of these!

Chris Williams

PS!

If you order one of these transformers suggested in my eBay link to repair your meter, I'll post back with suitable wiring instructions at a later date, but first of all, remove the old transformer from the meter chassis to begin with and post some more pictures of the space available please!

[arkeo]

Thanks a lot! I have a bunch of 12 V transformers and picked one around in a drawer. I felt not too confident to adapt the transformer to PCB but luckily there is much room inside the box and the workaround was straightforward (not too elegant but it works).

I made some quick checks and I think that I'll not try to align the instrument because the construction seems a bit poor and makes me think that it was a bottom line product. But if I'll find somewhere that the design is worth the effort, I may change my mind.

Thanks again, I appreciated very much your help.

[Chris56000]

Hi!

Glad you had a suitable transformer to hand to repair your meter!

I don't think you need to worry about the calibration of your meter – the 34401A is an excellent quality instrument whose readings can be relied on for many years once it's initial calibration is correctly done, and your Philips '2519 is almost certainly reading close enough for it's calibration to be within Philip's specified accuracy limits!

Enjoy your purchase, I'm always pleased to assist anyone who gets stuck!

Chris Williams