Had a bit of a disaster with the Philips PM6645 counter I acquired this week, accidentality shorted the supply for the NIT* to the display logic.
Before this it was sort of functioning, but seemed to have a problem with the decimal point, a possible faulty NIT, the lamps for the gate & frequency range are mostly blown as well, the only working one "kHz" is very dim too.
Before pictures of an approx 1MHz signal from a hp function gen & the correct reading from the 5245L.
Now it seems to be stuck in a reset state displaying zeros, apart from one NIT that is stuck on two.
The display board contain some obsolete 74 series 74176 & 74196 as well as standard 7490 that I usually find in frequency counter circuits, hopefully those are OK as I haven't got those, I do have some 7475 & 7490 & the NIT driver IC.
*term used by Philips in the "digital instrument course part 2" pdf that can be found on the web.
David
I have 3 x 74196 if you can't find any. I looked for 74176 but I don't think I have those.
Thanks for having a look for those, there does seem to be some old stock on ebay too, the 74176 is available from Europe or a dodgy seller that probably hasn't got any in the UK.
I've been working on the display counter board on it's own, so far I've confirmed the problem with the NIT stuck displaying a two as the 7475 having failed, that has now been changed, it does seem to count OK but only when the shorting link is added.
Think I need to find manual to progress this further, radiomuseum have the circuit diagram but it will take two months to download the set as I'm not a member and don't want to join.
Here are some teardown pictures as mine has some differences to the one on RM.
Logic underneath the display board and power supply section.
Input board with modification that has replaced three custom Philips IC's & a bunch of transistors with this extra board containing more custom parts? including a Plessey IC. Note the trouble someone had working on this.
Oven oscillator option and lots of spider webs in the background.
David