Teardown and troubleshooting:  P.G. Electronics PSA300 DC Power Supply Analyzer. - Page 1
Forum section: electronics / testgear

author: Spawn
author_rank: Frequent Contributor
timestamp: March 15, 2013, 06:44:19 pm
content: Original post:I was in a electronics dump shop today and checking some stuff out, I seen this Power supply analyzer from P.G. Electronics. Model number is PSA300.There was a note on it, saying “working but not fully” For its size it is really light weight, from the vent holes I could only see a PCB behind de control panel and huge cooling rib in de middle of the case. I did some search on internet and couldn’t find anything. I asked the shop worker he said he doesn’t know what the problem was in there he says it powers up but there is some problems he didn’t know what. It shouldn’t be complicated to be honest and shop is asking 50 euro’s for it.It is for testing DC power supplies till 60V and 30A, which sounds great. It has scope BNC connector for ripple measurement and I am not fully sure how the bananaplugs work, it need a reference voltage? or it is just connected with 4 wires from the PS you are testing, at least the image shows that.Anyone familiar with this? Before I commit to buy I like to know if there is some schematics for it.Sorry about the image, it was little dark in there and I took it with a phone:EDIT after purchase:Well it is on my bench now with its guts out. If anyone see something wrong which I didn’t see let me know please.Front panel:Nice fan, it is still working (LOUD):From above, the positive load input is on the heat sink nice way to connect the transistor, I think I need the schematics, because it is already checked by someone else and some things might be connected wrong:Shunt:Upper side of the PCB, any hobbyist does a lot better job making with a PCB, the traces are really thin, checked the caps all 470uF two 35volts and one 25volts, all 3 okay. Unfortunately I couldn’t replace them because the ones I got are 10volts (got it in a package).Other side of the PCB, looks like potentiometer is replaced once or they did really bad job on shorting its rod, soldered out and checked and works in all range, it is 5kOhm, as you see some fix is already done before, because of burnt traces:A trace is disabled by the last owner and another dodgy fix by last owner? :Found 2 burned out traces on same line, both fixed now, only ampmeter works now, and there is still full load so it didn’t fix much:NPN power transistors 2N3055:PCB where the transistors are soldered:Heat sink and the transistors while they were connected, I took it out and measured the resistance between positive and negative still measuring 0 ohms, next step is checking the transistors I guess:Like I said, if someone sees something wrong please let me know.

author: robrenz
author_rank: Super Contributor
timestamp: March 15, 2013, 07:22:39 pm
content: I think the reference volt connection is for the remote sense leads of the power supply you are testing.

author: Spawn
author_rank: Frequent Contributor
timestamp: March 15, 2013, 10:16:30 pm
content: That could be indeed, I have only one PSU with sense output.I am not sure if I should get it, but like I said it shouldn’t be hard to fix it. I don’t know how it loads with the PSU’s you test.

author: PA0PBZ
author_rank: Super Contributor
timestamp: March 16, 2013, 03:14:54 pm
content: I think I recognize that wall, Baco isn't it?

author: Spawn
author_rank: Frequent Contributor
timestamp: March 16, 2013, 03:21:07 pm
content: Yeap it isThey are not always the cheapest but I check there time to time.So what do you think, is it worth to get it?

author: PA0PBZ
author_rank: Super Contributor
timestamp: March 16, 2013, 04:28:00 pm
content: If you need something like this (as a load) I'd say go for it, it is probably not too bad if it's not burned up on the inside.Worst case you end up with some parts

author: Spawn
author_rank: Frequent Contributor
timestamp: March 16, 2013, 04:53:24 pm
content: Yeah I got couple power supplies and want to test some other stuff too. There is not much in there which is not replaceable I think, if some unknown parts are burned out need to do some reverse engineering I guess. I hope it acts good as a active load, like I said I can’t find anything about it so I am not sure on what principle it runs like with power resistors or something else.They are closed now so next day I can go there is 26 march other days I am working, I hope no one grabs itBut from what I understood it is sitting there for a while now. I hope this topic won’t trigger some of my countryman lol %-B

author: PA0PBZ
author_rank: Super Contributor
timestamp: March 16, 2013, 08:26:32 pm
content: Quote from: Spawn on March 16, 2013, 04:53:24 pmYeah, mentioning the place was maybe not the smartest thing to do, but I'll promise you not to buy it myself

author: PA0PBZ
author_rank: Super Contributor
timestamp: March 20, 2013, 07:31:41 pm
content: Yes, pictures is what we want... release thedragonpictures!

author: Spawn
author_rank: Frequent Contributor
timestamp: March 20, 2013, 09:33:02 pm
content: DidI Edited first post all pictures are there.I might need some help to find out what’s going wrong, a schematic would be great but I doubt if I can find any, checked couple things and fixed some burned out traces, more details in first post.

author: Bored@Work
author_rank: Super Contributor
timestamp: March 20, 2013, 09:59:17 pm
content: Looks like a hobbyist build, with most work going into the front plate. Maybe a circuit from some old electronics magazine?

author: Spawn
author_rank: Frequent Contributor
timestamp: March 21, 2013, 12:59:32 am
content: Doesn’t look professional indeed, however it says “Made in Italy” on the front panel, but it could be also a kit of course:I am drawing out the PCB layout on the photo’s right now, need to fill the components and the wiring to other stuff around, could take a while but, it will make more sense with a drawing to see what’s happening, this is how far I got, the image I work on is a lot bigger:

author: amspire
author_rank: Super Contributor
timestamp: March 21, 2013, 01:48:54 am
content: It probably has a shorted 2N3055. It should be easy to find.Put 1A into the output terminals, and find which one of the emitter resistors (the black coils of wire) on the heatsink PCB has a few tens to hundreds of millivolts across it. If the transistor is good, there will be no voltage across the resistor (less then 1mV).It looks like it was made as a special job for a power supply manufacturer. The board layout was done with tape on a plastic sheet - probably by the apprentice engineer or tech. The prototype PCBs were corrected and used in the final unit.

author: Spawn
author_rank: Frequent Contributor
timestamp: March 21, 2013, 02:27:53 am
content: Thanks amspire!I think the 3 of them is shorted, I don’t know what I am doing at this hour out of my bed because I have to work in couple hours but I took the measurement as you told, only the heat sink and the 2N3055 were not attached to the case/PCB so I measure directly. I will have to order these and wait till they arrive.Here are the results, 9.6mV and 87.3mV4.7mV and 0mV

author: Spawn
author_rank: Frequent Contributor
timestamp: March 21, 2013, 02:53:34 am
content: Okay, I was measuring wrongThe current through the PCB was enough to put some low voltage, but if I directly measure on the emitter resistors only the third one from left reads 75.4mV but since these are not expensive I will order couple more just as spare or even replace them all.

author: amspire
author_rank: Super Contributor
timestamp: March 21, 2013, 03:00:04 am
content: Quote from: Spawn on March 21, 2013, 02:53:34 amI was just about to suggest that - it is probably just the one 2N3055 that is faulty, but probably a good idea to get at least two transistors. It is a useful workhorse power transistor to have in your collection of parts anyway.

author: Spawn
author_rank: Frequent Contributor
timestamp: March 21, 2013, 03:05:10 am
content: Thanks again amspire, I hope that was the only thing, the burned out traces are already fixed, need to do some cleaning and when the 2N3055 arrives I will reassemble it again.

author: amspire
author_rank: Super Contributor
timestamp: March 21, 2013, 03:11:24 am
content: Quote from: Spawn on March 21, 2013, 03:05:10 amYou can remove the faulty transistor and then test the unit with remaining 3 2N3055 transistors. Should work fine.Just do not take it over 75% of full current.

author: Spawn
author_rank: Frequent Contributor
timestamp: March 21, 2013, 03:16:35 am
content: Great, my highest PSU goes till 10A that’s only 33% load. I will have to try that tomorrow after work. If I don’t sleep now I will be like zombie tomorrow, not a youngster anymore can’t take much without sleep

author: SeanB
author_rank: Super Contributor
timestamp: March 21, 2013, 05:48:54 am
content: Replace with 2N3773's, a better transistor.

author: Spawn
author_rank: Frequent Contributor
timestamp: March 21, 2013, 10:44:52 am
content: Thanks SeanB I will keep that in mind, one of my colleagues had a 2N3055 at home, he is a real EE so no wonder, I am an E too but much different current and voltage ratesI will get it from tomorrow, I am at work now, but tonight I will test the unit with one less transistor.

author: Spawn
author_rank: Frequent Contributor
timestamp: March 21, 2013, 10:04:19 pm
content: IT IS ALIVE!Thanks again amspire, removed the defective 2B3055 and it works great, only ampmeter is reading lower in low ranges at 0.6A and 3A, I did try to adjust it but it still was to low and of course it affects the higher current measurements.I was always eager to know how my crappy Yihua PS-3010D PSU would hold at its highest voltage and current (30V/10A) it is confirmed now and it is indeed crapit didn’t hold that good after 5 minutes it cut the current output and after 2 minutes cool down it start to work again.Had to use my Gossen didn’t want to risk a Fluke with it's 10A expensive fuse, and Yihua reads to high too… :

author: Spawn
author_rank: Frequent Contributor
timestamp: March 23, 2013, 08:59:09 pm
content: I am thinking to upgrade the analog current meter with more accurate digital current meter, this one is almost 20% off in lower ranges. Probably going for a extra shunt without touching the existing one, because of the reading for the PCB and adjustments from existing shunt. I could also replace the Volt meter to have same look at the front panel if I can find the correct sizes.Does anyone know the exact name for a red see through display filter? I can’t find anything on eBay. If I can’t find correct size panel meters I have to make my own front bezel and need this filter.

author: amspire
author_rank: Super Contributor
timestamp: March 24, 2013, 03:15:17 am
content: Quote from: Spawn on March 23, 2013, 08:59:09 pmOne option is to leave the meter as is. You should get much better then 20% error in the lower ranges - not sure what is going on there but you should be able to get reasonable accuracy.What you can do instead is to add two extra terminals to the case that connect to the current sense resistor - perhaps with some extra resistors and a pot to calibrate it for a convenient A/mV sensitivity. When you need to check the current accurately, just connect a multimeter to the new terminals and measure the voltage.

author: Spawn
author_rank: Frequent Contributor
timestamp: March 24, 2013, 04:53:51 am
content: I think scaling is not right amspire, the ranges on the switch and the current meter are not same either, meter has 4 scales and they added couple extra pots just for the current meter on the PCB.I already ordered panel meters with 7 segment red LED displays for current and voltmeter just to have vintage look, was a long search because there is way too much LCD panel meters but matching LED meters for both was hard to find. Meters have 0.5% accuracy and probably I will put the volt meter directly on the input instead of through the PCB that way I don’t need to use extra set of wires.I am not sure why the reference voltage has different input, because I thought it could be to keep current stable when you drop the voltage on same setting, but when I test it without any reference voltage input I can set it up at any current and change the voltage on the PSU and current stays perfectly same as it should be.The thing is I like to keep things original, so the idea is giving it original look and storage the old meters if I want go back to original meters, so there will be a lot cutting and sawing to use same bezel for both set of meters.

author: PA0PBZ
author_rank: Super Contributor
timestamp: March 24, 2013, 09:51:29 am
content: Quote from: Spawn on March 24, 2013, 04:53:51 amhttp://www.baco-army-goods.nl/meetapparaten/led-digitale-paneelmeter.html

author: Spawn
author_rank: Frequent Contributor
timestamp: March 24, 2013, 12:42:06 pm
content: Thanks PA0PBZI already ordered one, meter from Baco doesn’t have the right dimensions, the one I ordered fits in the original bezel, I think I forgot to mention the bezel is not attached to the meters, I need to make another bezel and put the new meter in there than I can put the meter from behind in the original bezel but I will also use a smoked Plexiglas to give a better looking finish.There is no earth connection in the main power cord, I need to earth the chassis so I will change that too.I got this voltmeter and a matching current meter with a shunt:

author: Spawn
author_rank: Frequent Contributor
timestamp: April 08, 2013, 02:03:14 am
content: Okay… I didn’t use the load for a while and today I wanted to test one of my PSU’s but the analyzer was fully shorted again, PSU was set on 1A, so I did a quick check and the transistor at same position was blown again. Last time I tested was 8A for a review and nothing more, I don’t understand what’s going wrong I didn’t fix it yet because of an another project I was busy on. Maybe a fast fuse in line with the transistors will help.Meanwhile I received the panel meters couple days ago, I need to do some milling to create a flat surface when the meters are in position. Still waiting on smoked foil to mask the display.