PM3262 oscilloscope repair - Page 1
Forum section: electronics / repair

author: sainter
author_rank: Regular Contributor
timestamp: April 01, 2015, 07:06:18 pm
content: Hi,At last found some time to repair second channel of my oscilloscope. The R1681 resistor was dead, It's 33R2 so will need to order it. A question about it, at local dealer i only find 1% 33R2, and I don't have a good multimeter to cherry pick the closest one of some batch. Is it better to order internationally high precision resistor or is 1% good. As I understand (from my limited electronics skills, if I can call it skill at all) it controls the voltage going to preamp of the second channel input. For testing I used 10 turn pot with more or less 33.2 turned.Second question, I fully cleaned all the switches and selectors I could find with contact cleaner (10 turn delay pot was crusty as hell). What else should I look at (because it's quite dissembled to take out the broken board). Is it better to change axial caps or should you only tinker with them if something is wrong?Was happy to find the manual:http://bee.mif.pg.gda.pl/ciasteczkowypotwor/Philips/pm3262.pdfIt helped a lotBy the way, do you think buying it for 60 Eur was a good deal or not ?Thx.

author: tautech
author_rank: Super Contributor
timestamp: April 01, 2015, 07:23:44 pm
content: You would hope that for 60 EUR it would have been working properly.The Service manual should have the resistor spec in the BOM, a 1% sounds good for the job.Check the PSU voltages are correct and any ripple meets spec.The main smoothing caps will be quite old (unless they've been replaced) and not smoothing the ripple .I wouldn't worry about any that are not associated with the PSU at this time.Each PCB is likely to have bulk capacitance also and you might like to check/replace these too.

author: sainter
author_rank: Regular Contributor
timestamp: April 01, 2015, 07:33:55 pm
content: Thx, will change PSU caps, It was a bit noisy i think.In my county there is an absolute shortage of used lab equipment. I had to look for a year or two before I Found this one. There a some Russian made scopes to buy (bought C-112A for 18 Eur, but It's only 1 channel 10 MHz scope) but they a few.I so envy people finding good deals on all kind of stuff on ebay and auctions (buying from ebay is out of the question, because shipping is very expensive).EDIT: btw can axial caps be changed for standard electrolitic caps of they must be the same?

author: tautech
author_rank: Super Contributor
timestamp: April 01, 2015, 07:49:59 pm
content: If you can source axial, it makes for a tidier repair, but that's up to you.You should measure ripple and compare with manual spec before replacement of caps, that's what the spec is for.Use a DMM set to ACV on a low(mV) range.You have a good quality unit, some that know them better than I might say only fix whats broken in it, probably also good advice.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: April 02, 2015, 06:25:40 pm
content: I have a bunch of axial Philips Caps here, which I don't need. My Philips Scope has fresh caps in it.Send me a message, if you want them.

author: KJDS
author_rank: Super Contributor
timestamp: April 02, 2015, 06:40:46 pm
content: I suspect that a 33R 1% resistor would work well enough, it might not be perfect but if you have one available it's preferable to waiting for something 0.6% different to arrive.

author: sainter
author_rank: Regular Contributor
timestamp: April 03, 2015, 05:02:01 am
content: Ordered 0.1% 33R2, better wait a week then have a problem with it latter.

author: sainter
author_rank: Regular Contributor
timestamp: April 13, 2015, 05:43:49 am
content: Ok, next problem. 100 nF 10% 250V polyester film cap is no moreQuestion would be- can i stick anything with this rating of polyester film has something important about them?

author: tautech
author_rank: Super Contributor
timestamp: April 13, 2015, 07:26:58 am
content: http://www.aliexpress.com/item/Free-shipping-20pcs-lot-CBB-capacitor-250V-104-100NF-0-1UF-pitch-10MM-Polypropylene-Film-Capacitors/1554972346.html

author: sainter
author_rank: Regular Contributor
timestamp: April 13, 2015, 12:02:47 pm
content: I understand that you can buy film caps, but wanted to ask, is it necessary to use film caps, or is it possible to use other type? If no, (for the purpose of knowledge, what spec. film caps do have that make them irreplaceable), then will have to wait few months to get them

author: Shock
author_rank: Super Contributor
timestamp: April 13, 2015, 06:25:53 pm
content: These two links may help.http://en.wikipedia.org/wiki/Types_of_capacitor#Comparison_of_typeshttp://www.radio-electronics.com/info/data/capacitor/capacitor_types.php