Philips PM6650 Counter/timer with dead A input - Page 1
Forum section: electronics / testgear

author: sbprojects
author_rank: Contributor
timestamp: November 09, 2021, 12:22:34 pm
content: Recently I've bought a beautiful PM6650 timer counter from Philips. Alas the A input is dead. The PM6650 is one of the rare instruments that returns a blank on the net. Can anybody get me a copy of the schematic diagram of the input amplifiers please? I wouldn't say no to a copy of the scan of the entire manual either, if any of you has one.

author: Gyro
author_rank: Super Contributor
timestamp: November 09, 2021, 12:35:20 pm
content: Hmm, it does appear to be a rare one [Edit: Strange not to even be able to find an image of it]. The usual manual sites bring up service manuals for several PM66xx models (it was quite a wide range though). Hopefully you can find one with a sufficiently similar input amp...http://www.ko4bb.com/getsimple/index.php?id=manuals&dir=Philipshttps://bama.edebris.com/manuals/philips/P.S. Any chance of a photo? What maximum frequency is printed on the front panel?

author: C.J.S.
author_rank: Contributor
timestamp: November 09, 2021, 01:06:14 pm
content: Quote from: Gyro on November 09, 2021, 12:35:20 pmDid you try google?QuoteSee photo below. Front panel says that max frequency is 512 MHz.

author: sbprojects
author_rank: Contributor
timestamp: November 09, 2021, 01:12:46 pm
content: There are only a few pictures on the internet, below is the best I could find. Currently I'm not at home so I can't take a picture of the actual instrument. And this is an Hungarian web site with the only information about the counter I could find on the nethttp://regimuszereklhanzi.5mp.eu/web.php?a=regimuszereklhanzi&o=2wEQJ_zWSw.The frequency range of input A is DC to 160MHz. Input B is from 5Hz to 160MHz if I'm not mistaken. And input C is from 5MHz to 512MHz. Inputs B and C are working.

author: Gyro
author_rank: Super Contributor
timestamp: November 09, 2021, 01:23:12 pm
content: Quote from: C.J.S. on November 09, 2021, 01:06:14 pmNo, I use DuckDuckGoQuote from: sbprojects on November 09, 2021, 01:12:46 pmIt might be worth checking out the PM6652 / PM6654 then. They list A and B as 120MHz, not too dissimilar even though they look more advanced.P.S. It looks as if the display is a Panaplex rather than LED(?). If so, it may be the same vintage as the PM6622 (80MHz)

author: sbprojects
author_rank: Contributor
timestamp: November 09, 2021, 01:37:53 pm
content: It is indeed a panaplex display. The instrument is in a rather beautiful condition. It has no latches. So you can see it count, then the display freezes until it has to count again. Real vintage. The 6652 is far too modern.

author: Gyro
author_rank: Super Contributor
timestamp: November 09, 2021, 01:51:27 pm
content: Yes, their older ones are lovely. All discrete logic, no fading EPROMs to worry about. You can change the display counting behaviour with the Memory button irrc.My PM6622...https://www.eevblog.com/forum/reviews/lets-see-your-nixie-tube-equipment/?action=dlattach;attach=244012;image

author: sbprojects
author_rank: Contributor
timestamp: November 10, 2021, 08:41:56 am
content: Thanks Gyro. Indeed the Memory button changes the counting behaviour. I didn't RTFM, because don't have the FM. My memory key has some trouble latching, needs some cleaning I guess.And the input amplifier of the PM6622 looks a bit similar to what I've seen on the PM6650. At least it features a dual JFET, which is my main suspect.

author: Gyro
author_rank: Super Contributor
timestamp: November 10, 2021, 01:24:17 pm
content: You're welcome. Yes a little TLC works wonders.A couple of quick and simple checks. Make sure the voltage little Out(?) terminal at adjacent to the trigger level knob varies sensibly when you adjust the knob, on both voltage ranges (and knob pulled and not). Also check that you actually have electrical connection between the BNC connector and the PCB (you should be able to read 1M resistance on the BNCs in DC mode without having to take the lid off). It wouldn't be the first time...Don't rule out the possibility of switch contact issues (or no-FM trouble) with the input trigger related push buttons either. Worth checking before assuming that it's the JFET.Lastly, don't forget that the counter has a check function which should at least exercise the trigger logic (though probably not the analogue front-ends).P.S. Looking at the picture, the PM6622/24/25 manual should be helpful for most functions, even if the control layout isn't identical.

author: WirelessESD
author_rank: Newbie
timestamp: October 04, 2023, 07:25:41 am
content: Hello I own a physical copy of the PM6650 manuals and have recently gone through the effort to digital scan the service and user manual.You can find them on:-https://museum.dantalion.nl/item/philips-pm6650-counter-user-manual-https://museum.dantalion.nl/item/philips-pm6650-counter-service-manualAs well as archive.org directly using:-https://archive.org/details/philips-pm6650-counter-operating-manual-https://archive.org/details/philips-pm6650-service-manualAppreciate if you also check out the rest of my museumKind regards