GWInstek GPS-3030D nasty intermittent fault - Page 1
Forum section: electronics / repair

author: Swainster
author_rank: Frequent Contributor
timestamp: October 21, 2022, 03:16:17 pm
content: Hi,hope someone can help me identify the fault with my GPS-3030D supply. It's particularly a particularly evil problem which occasionally seems to disable any regulation from the supply. In other words, I connect it to some device which needs power, leave it to do its thing then sometime later come back to a smoking ruin.Basically the symptom is that at some random time after turning on the supply, the output will shoot up to 40+ volts and the current will display 4+ amps (it doesn't necessarily output this current as it still shows this even with no load). Turning it off and on again doesn't necessarily reset this condition - it seems to recover just as mysteriously as it appears.During the latest episode I was able to turn the supply on and off a number of time and move it between desks and even from home to my office workbench without clearing the fault, only for it to recover after a few minutes when I had it left it open and powered up on the bench.I tried wiggling various connectors to see if it could provoke the issue again but no luck, plus as far as I can tell, the fault doesn't seem to be related to mechanical vibration.So... anyone experienced this issue before? (And hopefully solved it)

author: SkyMaster
author_rank: Frequent Contributor
timestamp: October 21, 2022, 08:40:47 pm
content: I have a GPS-3030DD, it is Dual Display but probably identical inside. Mine has no problems, but I am really interested to know what is causing the terrible behavior you are describing.

author: srb1954
author_rank: Super Contributor
timestamp: October 21, 2022, 11:02:27 pm
content: Quote from: Swainster on October 21, 2022, 03:16:17 pmThe time taken to recover from the fault condition seems to suggest that is it a thermal problem causing the fault. It could be a cracked component, bad solder joint or broken track that is breaking as the temperature increases.Set up the PSU with a load that can withstand the over-voltage condition and with external metering to verify the over-voltage and/or over-current. Use a heat gun to apply heat to various parts of the circuit to try and provoke the fault. Once the fault occurs you could then use a freeze spray to try and pin-point the exact component at fault.

author: Swainster
author_rank: Frequent Contributor
timestamp: October 22, 2022, 02:49:00 am
content: Yep, i think the 3030DD should be almost identical inside. This is indeed a particularly annoying problem as it burnt the tracks off my robot vacuum docking station PCBA before i realised what was happening. Luckily the docking station has over voltage protection so the damage wasn't transferred to the vacuum cleaner itself.Regarding thermal loading, that sounds like an excellent suggestion... only problem is that a friend is currently borrowing my (aliexpress) electronic load, but I should be able to cobble something together with power resistors... although thinking about it, given the nature of the fault, a constant power load would be safer... Anyway, will try it out and report back

author: Swainster
author_rank: Frequent Contributor
timestamp: October 26, 2022, 07:07:01 am
content: Quick update:1) I borrowed a 24W Resistive load from another project to warm things up... so far, after a few days testing I've not seen the issue spontaneously appear.2) Early on in testing, I saw the issue appear on start up a couple of times. Thinking about it, the power supply was in a common area at home (keeping the robot vacuum going while I repaired the charger's own internal power supply). It's quite possible that the bench supply was power cycled via the mains connection by the mother-in-law. This means that this issue may not be quite as nasty as thought i.e. only happens on power up, not spontaneously during operation.3) Not been able to reproduce it recently - perhaps all the fiddling has disturbed some bad connection.Other observations:1) The supply intermittently emits a noticeable "pop" on power up. Seems to be comming from near the front panel. Could be something to do with the hard power switch?2) Confirmed that the max no load output from the rectifier (before regulation) is 48V i.e. matches the observed faulty output. This requires the relays to be energised correctly (if no relays are energised then the no load rectifier output is more like 20V)3) When the fault appears the front panel current reading is either -1 (low range) or 4+ amps (high range), even when no load is present. This suggests that the fault also affects the current sense circuit. Voltage reading matches actual output.4) Unplugging the main front panel connector results in zero output.Parting thoughts:1) Wish I had a proper schematic2) Could be a failing adjustment pot? However I'm not that keen in giving them all a good twiddle as I don't have the calibration instructions...edit: Just to be clear, I'm not giving up on this yet. Will be keeping it on the bench and poking at it now and then

author: electr_peter
author_rank: Unknown
timestamp: October 26, 2022, 01:19:05 pm
content: Check that front panel potentiometers are not broken. I have seen similar supplies with poor front panel mechanical construction break potentiometers. If potentiometers break, PSU can enter open loop mode with max voltage at the terminals.

author: Swainster
author_rank: Frequent Contributor
timestamp: October 28, 2022, 04:51:21 pm
content: Hi electr_peter,It's a good idea but looking at the schematic, I believe that on this model, a broken front panel pot will cause the voltage to rise to the max programmable voltage, not open loop (I.e. the feedback loop doesn't go through the front panel controls). Disconnecting the front panel altogether causes the voltage to hover near zero as the ref input to the voltage control op amp is left floating.The fact that the fault shows open loop symptoms does indicate that the feedback loop is likely to be involved somehow. As a quick check I've swapped out the LM301A voltage control amp just in case it helps (i keep this part in my spares collection). Too soon to tell if it has helped yet.Actually my most recent 'theory' is that the original LM301A is occasionally going into phase reversal on power up. That could indicate that the fault is with the zener across the op amps inputs. So far no measurements to support this - I haven't even looked at whether the LM301A is able to go into phase reversal yet.Edit: haha, a quick look at the TI datasheet suggests LM301A is not subject to phase reversal/latch up, so I guess that idea is off the table

author: Swainster
author_rank: Frequent Contributor
timestamp: November 01, 2022, 06:04:49 am
content: Good news - I think I've solved this problem. I found a dry soldered jumper (actually the jumper hadn't been properly inserted into the single sided board). After many years of service it must have finally lost contact. This jumper carries the -15V supply from the regulator to the various op-amps, so when it was open all the op-amps went crazy, hence the weird current reading as well as the unregulated output.The jumper is question has been re-soldered, along with another suspicious looking one, and everything has been buttoned back up (plus I put the orginal LM301A back in). I will keep the supply on the work bench for a few more days just to confirm the fix, and if the fault returns then I will report back here.RegardsStephen