Digimess 3040 PSU

[Andy peace]

Hi guys.
I thought I would ask for some help here.
I have a nice Digimess 3040 psu. Although I've had it for four years I have NEVER used it until the other day when I went yo use it! .
well it all powers up fine but the voltage does not stabilise ?
It jumps about up and down and does not fix?
I'm not sure why this has happen but clearly it did not like not being used??
Any ideas please?
Many thanks
Andy

[CJay]

Forgive me but I've no idea how much experience you have so:

Be careful, that PSU will have deadly high voltage DC present when plugged in and also possibly for some time after it's switched off.

Depending how it's been stored I suppose it could be tarnished contacts on a control or a dried out capacitor somewhere.

There's a thread here with schematics and information for one of these that's 'blown up' but that's not the problem you're having.

https://www.eevblog.com/forum/repair/am3040-repairteardown-and-a-few-questions-on-smps's/

First thing to check on any switcher is the small value electrolytic capacitors and high value resistors as well as looking for any sign of scorching on the boards and components.

Did you buy it new, second hand, spares repair? Would the previous owner be able to confirm it was working before they sold it to you?

[raz221]

Hey Andy, and welcome to the forum!
Anyhow, there is clearly something not working properly inside the unit.
Probably a resistor, capacitor or diode. In order to properly troubleshoot it, you'd have to open it.
You'd also need a multimeter, a capacitance meter a capacitor discharge tool, a soldering iron and knowing how to use all of em accordingly.
Now, I could be wrong, but judging by the way you've put it, it sounds like you don't have any prior experience with
troubleshooting & repairing electronics, so this could be a very steep learning curve for you.
You might be best taking it to an expert or some local electronics repair shop.
But if you insist on doing this yourself, I could definitely give you some pointers, as well as recommendations on what equipment to buy.

[Andy peace]

Hi guys thanks for replies.
Well I am a service tech, but with copiers . But with those. If a power supply goes down we put a new one in!  Very modular kind of work so not much component level diagnosis  unless it's obvious but as I said even then we never repair pcbs we just change them !
I am confident with electronics but to be honest I have no idea what is wrong with this psu?
I purchased it NEW four years ago to power a 28v amp but it's a project that never happened,  I did test the amp twice then put it away. Stored carefully just not used until the other day when the fault showed itself.
I did remove the covers and the psu is immaculate inside, no dust no burns all components look like new!
But as suggested it's probably gone dry somewhere as didn't like sitting unused.
Shame as I paid £300 for it !!
I thought if I opened her up I would see a potential fault but really I could not ?
 Many thanks
Andy

[raz221]

I did remove the covers and the psu is immaculate inside, no dust no burns all components look like new!

As they say "looks can be deceiving"
There has to be one or more failed components in there.
Physical indications are not always present in such cases.

But as suggested it's probably gone dry somewhere as didn't like sitting unused.

Electronic components can fail regardless to how often the device is used actually.
There is of course an increased risk of that happening when the device is in regular use, but it can happen either way.

I thought if I opened her up I would see a potential fault but really I could not ?

Never heard anyone referring to a bench PSU as a "she" before, lol!
Anyhow, it is what it is, you have 3 options here:

1. Take it to an electronics repair shop - they'll know how to troubleshoot it and get it fixed.
2. Buy the right equipment, be ready to learn the "ropes", and maybe eventually, you'd be able to get it fixed yourself.
3. Let it go and get rid of it.

[Andy Watson]

I would contact Digimess in Derby - see if they have any economically viable options for restoring the unit to working condition.

[Anks]

Or just ask someone  with a modicum of sense to fix it then the it can continue its bat shit idea of being a power supply

[grumpydoc]

It's a Mastech one - recent discussion threads on these designs include https://www.eevblog.com/forum/repair/mastech-hy5020e-50v-20a-bench-supply-economical-to-repair/ and
https://www.eevblog.com/forum/repair/am3040-repairteardown-and-a-few-questions-on-smps's/msg639535/#msg639535 - the latter has the schematic for the 3040.

Or just ask someone  with a modicum of sense to fix it then the it can continue its bat shit idea of being a power supply

Yeah, they aren't the greatest.