Philips PM6680 power board - Page 1
Forum section: electronics / testgear

author: Ypsi
author_rank: Contributor
timestamp: July 13, 2019, 07:46:01 am
content: Hi boys!I bought damaged PM6680, and found problem on power board. No voltage on secondary side... Founded three cracked SMD resistors /??/ on primary side.However, i can't find any documents about powerboard with /most likely/ old version. All documents what i found describes only version with UC3842, but my board is with 4069 as a driver chip.If anyone has this documentation for powerboard with 4069, i will be very pleased for looking on.Thank you!!

author: tautech
author_rank: Super Contributor
timestamp: July 13, 2019, 07:59:07 am
content: Welcome to the forum.Nope, look harder and give us better/more pics. You're missing something as HEF4069 is a hex inverter, a logic chip and not suitable for a SMPS controller.

author: Ypsi
author_rank: Contributor
timestamp: July 13, 2019, 09:19:50 am
content: Thank you for the answer. Here is the album link for more pictures:https://photos.app.goo.gl/Ka3TRrdwX3fqQ7sg9.Yes, i know, 4069 is the classical logic chip and is confused for me why is used in this topology...New versions uses UC3842 /or something similar/ in standart circuit.

author: tautech
author_rank: Super Contributor
timestamp: July 13, 2019, 09:31:04 am
content: Is the SMPS controller the 8 terminal black TDK package or is it just a mains filter ?Just Googled the 112F8E on it, no joy.

author: Ypsi
author_rank: Contributor
timestamp: July 13, 2019, 09:46:43 am
content: Hmm, it can be something as controller... Mains filter is located outside this powerboard...

author: CDaniel
author_rank: Frequent Contributor
timestamp: July 13, 2019, 10:44:22 am
content: Yes , that black box should be some kind of controller ... and many , many small transistors + 4069 , very unusual power supply . You have to measure every single component for obvious shorted transistors or blown resistors ... But the whole thing should be possible to replace if no luck trobleshooting

author: Ypsi
author_rank: Contributor
timestamp: July 13, 2019, 11:27:10 am
content: Thank you boys for answers.Cracked components was caused by wrong dissambling of the powerboard by original owner. No components was damaged by fire, or short circuit... Only mechanical crack by the scredriver .But, some new facts. I tried to use 3 pieces of 22k resistors instead bad SMD, and powerboard runs up!But i still think that no good way, however it shows that is no other components damaged.I will inform about next steps.Thanks!

author: TurboTom
author_rank: Super Contributor
timestamp: July 13, 2019, 11:43:15 am
content: Quote from: CDaniel on July 13, 2019, 10:44:22 amEven though the OP solved the problem, some comments on the PSU: I bet my bottom dollar (or Euro that is...) that the black TDK brick is a gate/base driver transformer. It appeares the PSU is a half-bridge topology and as suggested by the OP, the 4069 is really somehow used to control the primary side. Philips is (or rather ...had been...) notorious for coming out with the weirdest designs that were very awkward to reverse engineer, let alone understand even if a schemantic was available. Moreover, their products had a very distinctive design so they could be identifyable as Philips even if there wasn't any label or imprint telling so. Once in a while, I love poking around in old philips gear, for that reason I keep an old PM3234 analog storage tube scope in my TEA collection. Pure nostalgy...

author: ArthurDent
author_rank: Super Contributor
timestamp: July 13, 2019, 02:11:32 pm
content: I bought a very dead PM6680 counter real cheap and the switching power supply was badly burned with a number of components damaged beyond repair, like the transformer. The A.C. to D.C. part of the supply is on the motherboard outside the power supply cage so the supply inside the cage is basically a high voltage input D.C.-D.C. converter. I gave up on repairing the supply but came up with a scheme that worked. Where I'm only going to be seeing 120vac input in the U.S., the replacement supplies didn't have to be wide input range and the nice Cosel supplies I used were 85-125vac rated input.This is where it got tricky because I wanted to use parts I had on hand and not put a lot of money into this project. I needed +5,+15,and -7 volts to run the counter. I wired a +5 Cosel and a -7 volt Cosel for two of the voltages and used a 12 volt input, 15 volt output D.C.-D.C converter for the third. With the 12 volt input of the 15 volt supply wired between the -7 volt to the +5 volt outputs from the two Cosel supplies , I got the 12 volts input I needed for the +15 volt supply and it worked great. All the supplies output more current than I needed so they run nice and cool. Here is a photo of the repair I did.

author: Ypsi
author_rank: Contributor
timestamp: July 13, 2019, 05:04:45 pm
content: Arthur, it's not bad idea, i purchase few DC-DC converters, and i will try build something as original powersupply.Now i testing repaired board, and we will see...Thanks!

author: Ypsi
author_rank: Contributor
timestamp: July 23, 2019, 10:59:33 am
content: Hi friends. After 9 days of testing is counter still alive with original repaired powerboard. I hope that he has back in live for a long time..Thank you!