LeCroy 7200 PSU smoke - Page 1
Forum section: electronics / repair

author: shakalnokturn
author_rank: Super Contributor
timestamp: August 22, 2018, 09:31:35 am
content: I'm currently moving, the other day I pulled out my first DSO from under the desk where it had been collecting dust for a few years, thought that it was of considerable volume and hadn't been used for too long.So I decided it was time to try to sell it, when I powered it up to take some photos it let some thick grey smoke out of the back. (Looks like the scope doesn't want to leave me...)I opened it expecting to find a cracked RIFA line filter but there was none. The PSU is a real PITA to disassemble, the culprit was found fast enough: A shorted tantalum drop on the secondary.It took more time to clean the burns than actually troubleshoot/repair. While in there, I made the most of it to clean some connectors and refresh some weak solders, that had signs of heating.Note that the under-side has plenty of clearance between primary and secondary traces, but on the top side clearance is much reduced, the bad tantalum (secondary) melted through the plastic sheath of the primary bulk capacitor it was next to.

author: Zucca
author_rank: Unknown
timestamp: August 22, 2018, 10:06:15 am
content: nice, will you replace also the melted primary bulk capacitor?

author: shakalnokturn
author_rank: Super Contributor
timestamp: August 22, 2018, 10:44:53 am
content: Quote from: zucca on August 22, 2018, 10:06:15 amNo, can't be bothered to search a replacement, besides the bulk cap is not defective, I stuck a few layers of Kapton tape over the hole, that is probably already safer regarding melting isolation than the design was in the first place.Not that it is really unsafe for the user, as the scope is meant to be earthed, at the worst if isolation was lost through the bulk cap's can it would probably only cause more damage to the PSU, all the same I consider this as a little bit of a design overlook...

author: Zucca
author_rank: Unknown
timestamp: August 22, 2018, 11:10:00 am
content: Sometime I just replace components because they look bad even if I know they are ok.There is a kind of magical unwritten (EE) gold rule: if it is bad for the eyes it is or will be also for the device.

author: shakalnokturn
author_rank: Super Contributor
timestamp: August 22, 2018, 11:30:17 am
content: Quote from: zucca on August 22, 2018, 11:10:00 amI can understand liking things to look neat, however sometimes it is just not worth the bother (and I do not have enough spare time right now to make the insides of a closed frame PSU with a crap design look cute).I'm not of those who shotgun electrolytics for the sake of it, and when repairing vintage audio amps I'll even leave electrolytics with shrunken sheathing in place as long as they measure OK and the exposed can is not a risk to me or surrounding components.All the same your rule does apply in many cases...

author: Zucca
author_rank: Unknown
timestamp: August 22, 2018, 12:20:59 pm
content: I agree with you shaka...If you are in the mood of wood...https://www.dhtrob.com/projecten/elna1_en.php

author: shakalnokturn
author_rank: Super Contributor
timestamp: August 22, 2018, 01:23:17 pm
content: Quote from: zucca on August 22, 2018, 12:20:59 pmWell... some people do go over the top a little, sure looks better, so it must sound better. (Lacks a little blue light maybe?)I used to do that, now I have GMO bamboos that grow the capacitor themselves. Cut a chunk, add solder paste and you have audiophile gradeB.S. capacitor.