Philips PM6668 frequency counter -display problem - Page 1
Forum section: electronics / repair

author: wedgetail
author_rank: Contributor
timestamp: June 21, 2025, 06:50:05 am
content: After many years of storage I have looked at a PM6668 that I meant to modify/repair, but gave up at the time for lack of time to look harder. I think the problem may have been the same.I have a feeling I may have been thinking of attempting modification as referred here, also from here I made not of the 'display replacement' Part number Philips display 5322 130 9402https://www.sbprojects.net/projects/sb6668/sbbuscontrol.phpThe model I have has a battery, which I think may be dead, not looked inside yet. I have downloaded a couple of manuals so I have a lot of information. I has been on charge for 10 hour plus, but no sign that battery is taking over when removing power cord.Anybody here that have experience with this model and done service I am keen to hear to figure my next step

author: andrewtaylor
author_rank: Contributor
timestamp: June 21, 2025, 12:53:17 pm
content: The lo bat indicator in the right Side of the display is....saying everything.Chg. battery NOW

author: factory
author_rank: Super Contributor
timestamp: June 21, 2025, 01:38:25 pm
content: Battery seems to be a 6V lead acid type, probably shorted or partially shorted, causing the strange display.David

author: wedgetail
author_rank: Contributor
timestamp: June 21, 2025, 02:18:05 pm
content: Thank you both for posting. I have just finished scanning the manuals I have, reading a bit here and there.1.. I thought the odd display indicated I may have bad display, it did earlier change slightly every time I turned front panel power on and off. This may have settled down as now it seems to be steady same display.2.. I was wondering about the battery unit, theoretically I thought removing the battery unit would be a start as I was hoping to get power restored. Can confirm the battery is a 6V unit according to the manual.It is past midnight here in Australia, will see tomorrow. I will removing the cover and look inside.

author: factory
author_rank: Super Contributor
timestamp: June 21, 2025, 02:42:30 pm
content: You would need to find out if it's designed to work without a battery fitted, I can't comment further as we had some 6667 at work without that option. From memory they were a bit temperamental and I remember one of them giving an error code that wasn't in the manual, it reset after a power cycle.David

author: wedgetail
author_rank: Contributor
timestamp: June 23, 2025, 10:21:30 am
content: A bit more work on the manual, trying to convince myself that removing the battery unit will/should allow the PM6668 to work on mains connection only. Will p[lace 3 pictures here for that purpose.Not sure what happened, but had trouble placing 3 files in one go, think I have got it right.Having had a look at replacing the display with a 16 character single line or 8 character 2 line display as no hit trying to find a a single line unit that has all individual segments available to 'handwire' from the 3 ICs SSA1062 doing the job at the moment.At the moment I have no room to remove the cover in my lab, it is choker full have to stand up, PM6668 taking over the seat. I am trying to make a dramatic cleanout, how the PM6668 got 'found again'

author: Haenk
author_rank: Super Contributor
timestamp: June 24, 2025, 10:15:09 am
content: I have a PM6666 that originally came with a battery option installed, which was - of course - dead and brought down the whole device.Removed the Nicads, unplugged, and put the whole carrier/stuff back in, for keeping it as original as possible.That solved the problem of "not running".

author: wedgetail
author_rank: Contributor
timestamp: June 24, 2025, 02:07:05 pm
content: HaenkThank you for information, I will look into this counter. Got the service manual and also a very nice write up on the unithttps://lajtronix.eu/2019/10/14/philips-fluke-pm6666/

author: wedgetail
author_rank: Contributor
timestamp: June 25, 2025, 12:44:08 pm
content: Update, cleared enough desk space allowing me carefully to take the unit out of the case. Allowed me to check the battery voltage, only a residual voltage of less than 1.5V. I removed the battery unit from the unit, removed the battery from bracket and tried to charge with a constant 100mA from a Hewlett Packard bench supply.Before I removed the battery unit I found out that applying mains power by connecting the IEC connector and then pusing button from STDBY to ON I believe I saw the display go through a very quick check before all digits showed zero. That was a big surprise, just taking it out of the case made the display 'come right'.However the battery voltage measured 7V, the over voltage limit and operation shut down I believe because the kHZ, MHz, and LO-BAT icons turned off.I studied the manual rather closely and believe I have convinced myself that I should be safe applying mains power when battery unit removed. I will sleep on this and go through making sure I have got it right one more time.

author: wedgetail
author_rank: Contributor
timestamp: July 04, 2025, 09:05:01 am
content: Good news on the PM6668 counter. Finally figured out the schematic diagram and combined with a not in the service manual about removing a 7805 voltage regulator before installing the battery unit. Took me quite a while before I noticed this regulator not installed when battery unit installed.Then the schematic made sense. I applied mains power, measured approximately 4.95 V. The worked and the quick start test showed me the display worked fine. After a days running the counter I installed it in it case again.When I turned power on again, it did not work. Gave a bit of head scratching but accidentally it sprang alive again. I realised soon there was an intermittent associated with the pre-scaler board. I think it is the multi pin connector joining the board to the main electronic board.Now when it happens I give the case a gentle knock on the side and counting restored. I will need to find time to open up box again and remove pre-scaler board.