Volteq HY series bench supply, wrong current display

Did you check out the A/D reference?

RL

Sounds like a typicall issue for these supplies. We use quite a few of them and have seen this problem too.

The schematics are still good enough to at least try and fix them.

I can see some design flaws especialy in their output current limiting that can break the output FET if you short the output at high voltage.

boB

Looks ok. The main board is sending a voltage up to the ADC for the current display which varies with the set voltage (but shouldn't). The current signaling runs in the tens of millivolts which was a poor design decision and they had to add a CM toroid, probably to get that quiet.

I could try but got so many projects already. I was hoping someone would say "Oh, that happened to me as well and the fault turned out to be ..."

Yeah, the design is sub-optimal. Many of the parts are pretty robust though and they gave it a way more massive heat sink than my ham radio SMPS.

Hi Joerg, My first inclination is to check the current-sense resistor "R206". That alone, if raised in resistance, or opened up, would cause such behavior. = RS

Rich S wrote: =================

The posted schem is illegible.

..... Phil

Click on the PDF link after the schematics images

In Schematic, it looks like current sensing is completely independent

- A jellybean 7107 circuit. No controller influence.

Check isolated supply levels for this section.

RL

Gentlemen, found it. It wasn't just one poor solder joint but three. All in the connection from the big current shunt to the 7107 display board for the current display, plus one on the voltage display board. Not sure how but this also caused the power supply to lock up.

If someone else has that happen: Check the blue and black wires going through a toroid towards the back of the unit. They measure sort of ok but give them a tug near the solder joints and the resistance changes.

I can't remember when I last saw such a poor solder job. Basically consisting of splats and dull blobs. I'll have to take the whole thing apart and resolder the wires. Considering that they also jammed in lots of the screws because many things didn't line up that won't be fun.

Glad you found it. (I mentioned that resistor first, since I always check high-power parts first; And, it seemed like the PS output was zero, with any load,)

ALWAYS first assume solder joints are a cause and re-solder anything remotely suspicious. In a mass-produced product, the solder-process QC is too easily 'relaxed'; and weak joints can be hard to detect.

Actually when troubleshooting, there is a long list of basic steps. Here on sed, I tend to assume these were checked off.

Would we benefit from a "s.e.d.-level" repair FAQ?

regards, RS

Even the Chinese can have a bad day once in a while.

watch the guy soldering at 23:01-23:05

snipped-for-privacy@fonz.dk wrote: ===================

That iron tip must be glowing red to go so fast, just look at the smoke coming off, Terrible, crazy idea.

..... Phil

Aha - the detective Lasse, scores again. Thanks! well said, Phil! they are may get joints that Look ok, on the surface, but.. what darkness lurks beneath?

Soldering is a chemical and mechanical process. You can speed up the chemical reaction with higher temp, up to a point. (...Until you degrade the flux, the PCB, etc.) But the mechanical? there's that physical thermal time constant of the assembly.... regards, RS

if you are paid by how many you can make in a day it is a great idea ..

snipped-for-privacy@fonz.dk wrote: ===================

That manager guy looks like he would be more at home running a brothel filled with 12 year old girls. Maybe he does that too.

...... Phil

It wasn't zero, you could set the voltage correctly until it locked up with a fake overcurrent depending on potmeter settings. The solder problems are in the cable path but also in the ground cable path of the voltage display.

You sure could call that soldering style "relaxed" :-)

Well, you can't always see it, only after I used the mirror from my Bernstein set. I was hoping someone had experienced the same thing. Meatime I found yet another bug, a ceramic capacitor is "touchy" and makes the current display go crazy. So that also needs to be replaced.