I would just like to know if anybody have the PM6668 freq ccounter

Mine is showing problem with the display when I powered up, as it has a battery unit it could be the problem it seems, working my way through the manual.

However somebody may know the answer,  there are two counters  PM667, no battery unit and PM6668 with battery options.

The counters are 1985 abouts vintage, be interesting so see how far I can get with repair.  

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Hi plover,

I've seen someone with also a Philips device with LCD troubles. It seemed that after years the contacts will erode. Those little rubber strips with laminated carbon between the display and the pcb.

Marcel

Plover, could you post some pictures?

https://github.com/MagicSmokeBlog/Philips-PM2535-Kermit

Yes I will do but not sure when I can find time.  I just had a quick look at your link  

The concept will be perfect for my unit, though the amount of programming needed may be too much for me.  

Thank you it is great start

You may have a look at the counter in a project, not mine, giving the PM6668 a heart transplant, this was my starting point 15 years ago when I got the unit, it got put on the storage shelf until recently a major clean out started.

https://www.sbprojects.net/projects/sb6668/index.php

Hi,

Can't you replace the LCD with something like this.


 
Looks like the 6668 has a 8 numeric display.

I am convinced we could replace the 8048 with a pico, driving that display.

The pico's PIO can do the counting. All software in MMBasic.

Volhout
Edited 2025-06-25 05:32 by Volhout

Volhout

Very good idea, but personally I will be unable to handle the programming I am just getting too slow, think it has something to do with being 81 years old, bit disappointing but hey lets see.

I have just managed to get the battery unit removed, during taking counter out of the case I must have stirred something up.  While checking operation I turns out when pushing the ON button, display went through very quick check showing all segments and then settling down to showing all digits zero.

I will come back on the replacement displays, I would at least like to check out theoretically what would be needed.  In case it is just a new battery I need.it looks like being open circuit, the charge current then sent the voltage up to 7V 'over voltage limit' which stepped in and stopped operation.

Update on counter.

After removing the battery unit and scrutinizing the schematic diagram of the battery unit the penny dropped. In the schematic there is an 7805 5V regulator, which is removed when battery unit is installed.

I found a 7805 in my stock installed it in 30 second place in socket install a 3 mm csnk 3mm screw, washer and nut.

Turn on and measure 5V output but crazy display. Head scratching and accidentally knocking the counter I realised there was an intermittent associated with the pre-scaler board.  Gentle knock on the side of the case now installed seems to start proper operation.

this was a pleasant surprise as the pressure to look for modification and to replace display can be put off.