Philips combiscope PM 3365A failure - Page 1
Forum section: electronics / repair

author: drashiel
author_rank: Newbie
timestamp: July 14, 2015, 06:55:02 pm
content: Hi to everyone.My name is Miguel, amateur on electronics. I bough this scope on ebay six months ago and works fine until today. My knowledge on electronics is not too big (I used scope to measure PWM and other stuff on arduino boards) but understand the basics.Today during measurements, vertical deflection start to fail. Image on screen was compressed when scope was warm (unplug and wait until scope is cold made start to work again but about 10 minutes turn on, scope start to fail). If I tap the scope, magically repair itself, I think it's a matter of time that the fault is permanent.I have tried to reseat all connectors on XYZ amplifier (could be an false contact), but still happens. Everything looks fine, there is no blowed components or leaky capacitors. Have got service manual but I do not know where to start.Any help would be appreciated.Thanks.

author: kripton2035
author_rank: Super Contributor
timestamp: July 14, 2015, 07:43:42 pm
content: if it comes back when you tap the scope, then it's probably a dry soldier.open the scope, and try to tap more precisely to see on what card the bad soldier can bethen inspect this card and find the dried soldier and resoldier it

author: tautech
author_rank: Super Contributor
timestamp: July 14, 2015, 09:19:59 pm
content: The Tek troubleshooting guide in the first post in this board is good to have.PSU's should always be checked to meet specs on scope repairs. You can check for ripple on the DC supplies with a DMM set to AC volts.Often the schematics have DC voltages listed, be aware normally the scope must be set in a specific way for the DC voltages to be relevant. RTFM.For others watching the manual is here:http://elektrotanya.com/philips_pm3365a_67a_75_77_oscilloscope_sm.pdf/download.html103 Mb.

author: drashiel
author_rank: Newbie
timestamp: July 15, 2015, 07:09:18 am
content: Thanks tautech and kripton2035 for your inputs.As said kripton2035, resolder transistors on Y amplifier but not solve problem. Reseat connectors between preamplifier/adaptation unit board and seems to start working fine again.It is possible bad soldering appears 20 years after? (I thinks this units was build on 1995)Regards.

author: tautech
author_rank: Super Contributor
timestamp: July 15, 2015, 07:34:52 am
content: Quote from: drashiel on July 15, 2015, 07:09:18 amThe soldering has now been subjected to many thermal cycles since manufacture and it is not unheard of for joints to crack especially those that suffer any mechanical stress.Interconnects and other headers are worthy of careful inspection.But just thermal cycling will crack joints, particularly those not fully "tented" at manufacture.

author: HighVoltage
author_rank: Super Contributor
timestamp: July 15, 2015, 08:48:22 am
content: I just fixed a Philips PM3370B that had a bad power supply. So, I would start with the output rails and make sure all voltages are correct.

author: PaulAm
author_rank: Frequent Contributor
timestamp: July 16, 2015, 04:43:44 pm
content: Sometimes a component will develop a crack, possibly where a lead joins the body. These can be incredibly frustrating to track down. You need light, magnification, an insulated rod to tap components with and a lot of patience.I had a Tek 468 that I was working on that had a crack in a ceramic resistor network that behaved like that. Took me forever to find it.