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Forum Index : Microcontroller and PC projects : Old Philips PM6668 counter to 1 GHz --- in trouble
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plover Guru  Joined: 18/04/2013 Location: AustraliaPosts: 306 |
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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Marcel27 Regular Member  Joined: 13/08/2024 Location: NetherlandsPosts: 94 |
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 |
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| Marcel27 Regular Member Joined: 13/08/2024 Location: NetherlandsPosts: 94 |
Plover, could you post some pictures? |
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| Marcel27 Regular Member Joined: 13/08/2024 Location: NetherlandsPosts: 94 |
https://github.com/MagicSmokeBlog/Philips-PM2535-Kermit |
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| plover Guru Joined: 18/04/2013 Location: AustraliaPosts: 306 |
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 |
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| Volhout Guru Joined: 05/03/2018 Location: NetherlandsPosts: 5072 |
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 PicomiteVGA PETSCII ROBOTS |
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| plover Guru Joined: 18/04/2013 Location: AustraliaPosts: 306 |
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. |
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| plover Guru Joined: 18/04/2013 Location: AustraliaPosts: 306 |
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. |
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| Marcel27 Regular Member Joined: 13/08/2024 Location: NetherlandsPosts: 94 |
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