Missing Components inside Power Supply? - Page 1
Forum section: electronics / repair

author: .
author_rank: Newbie
timestamp: September 03, 2016, 07:44:42 pm
content: Hello everyone,I have been given a 'Deltron' bench power supply capable of 32V at 1A.This unit has clearly been roughly-freighted a long distance, as the nearly-10kg transformer inside [which coincidentally had no screws to secure it] has made scratches even in the top half of the case.. as such, the adjacent circuitry is just a little rough [a relatively common story, it seems] Anyways, here's the extent of the damage:And the same location, on the opposite side of the PCB:[Best shot I could get without further disassembly; I don't have a space anywhere to do so at the moment]The problem is mainlythe fact that Deltron was not exactly champs at documenting what they branded, from what I've found. Thusly I haven't yet sourced any documents relevant to even the 'RP' series of power supplies. Additionally, the only remnants of the red capacitor is the chunk in the picture; the crate in which this was given to me is void of any pieces of capacitor, or anything else. On top of that, there's yet another component missing as that one protruding lead would suggest, [I made an attempt at highlighting the probably-corresponding lead] however there are no remains of anything else that I could find, so I would definitely benefit from a suggestion there! I am not confident in assuming what should be where, even though all of these missing components appear to be after-the-fact additions which might explain how this unit was working "fine" when the last person had it. I should lastly mention that I was going to put a red [ceramic/tantalum?] 400v capacitor which I saved from a very old fake Cree lamp where the old one appears to have been, just to see what would happen, but I will wait for that.Apologies for any scattered words; I struggle to avoid them. Regardless, thanks for getting this far and have a good day or\then evening.addt'l photoshttp://public.fotki.com/Snow/deltron-rp30-1s--53711-/

author: Kleinstein
author_rank: Super Contributor
timestamp: September 04, 2016, 09:42:27 am
content: It is rather difficult to guess what cap belongs there and what else is missing. Form the position close to the power transistors, this could be a afterthought (and thus on the back) cap to reduce oscillations. These caps can be tricky to guess, even if you have a circuit diagram. The capacitance can matter and could be anywhere from 10 pF to about 10 nF, depending on the circuit.Without the schematics its really hard to tell what is missing, and even than one might need to do a simulation or/and measurements to see, what is missing / wrong. If you are lucky the cap is just extra buffering and less critical, at least that could be seen from the schematics.The resistor (100 Ohms ?) that is still there at the under side looks damaged too. At least this one is easy.

author: .
author_rank: Newbie
timestamp: September 04, 2016, 08:40:11 pm
content: Thank you for sharing your knowledge! I suppose I should invest in a scope which isn't 80 years old and do some testing. It is very relieving to know these aren't completely critical, as the person before me used this continuously, and I had assumed that they really might have damaged it.But thank you for letting me know; this will be a good way to start reviving and continuing my passion.. Thank you again for the input.Good day for now

author: Cyberdragon
author_rank: Super Contributor
timestamp: September 04, 2016, 08:45:48 pm
content: Why would they put large components on the back side of the board like that?If you have any trimmer capacitors you could experiment with the value untill the circuit functions properly.

author: Kleinstein
author_rank: Super Contributor
timestamp: September 05, 2016, 08:14:23 pm
content: One reason to put the cap on the back side is the need to adjust it, with no easy access to the other side. Variable caps in the nF range are really rare and large, so not that easy.If the capacitor is for a stability adjustment, it is well possible the supply works with well behaved loads even without the capacitor. But without the right size cap it might show more ringing or could oscillate with a more critical load. So it may kind of work without, but could fail unexpected with different loading.The first thing would be to get a schematics, at least for the part just around the cap. Today one can simulate the circuit and this way get a clue for the right size of the cap, maybe even better than it was possible by measurement.

author: .
author_rank: Newbie
timestamp: September 06, 2016, 10:43:04 pm
content: Yes I think that is probably one of the coolest things I have heard in a long time.. I will definitely invest in software if there is something decent for Linux.Also, one of the last hobbies my father had was collecting ancient radio equipment, so I have way too many variable capcitors.. but they are all metal so I don't know how much capacitance they may be. And off the topic...http://www.ebay.com/itm/Vintage-Radio-Shack-Probe-Style-Digital-Oscilloscope-Made-in-Germany-/361712304467?hash=item5437bbc153%3Ag%3AD1sAAOSw8oFXyikO&nma=true&si=GgMeyIz9egJyMsC7A45vb%252ByxoAs%253D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557I just bought this as a novelty.. [I am still looking locally for a decent scope] but I just wanted to share that here

author: bitseeker
author_rank: Super Contributor
timestamp: September 07, 2016, 01:51:24 am
content: For those who'd like to see the pen scope, I believe it's the same model that Dave showed in Mailbag #860

author: .
author_rank: Newbie
timestamp: September 08, 2016, 06:51:05 pm
content: Sorry to bump the thread again but I replaced the red capacitor and everything is happy [not hot, etc] but I replaced the 100+\- 10% with an equivalent one, only with +/- 5% tolerance, and the voltage gauge slowly rises even when its knob is at 0% when powered on, so I think I may have quite a bit of simulation / trials to do