Bench PS Problem (Volteq HY3010D)

[orientalsniper]

Re: Bench PS Problem (Volteq HY3010D)

It's 38V now.

Thanks for the help, here are the readings:

M2
1: ignored
2: 38V (same as displayed voltage)
3: 40V
4: 32V
5: ignored
6: 50V
7: 50V
8: ignored

M1
1: ignored
2: 38V (same as displayed voltage)
3: 38V (same as displayed voltage)
4: 32V
5: ignored
6: 38V
7: 50V
8: ignored

[eccerr0r]

Re: Bench PS Problem (Volteq HY3010D)

Okay, based on the data you provided here, it looks like your control pot or that part of the circuit is bad, and your op amps are probably fine (Did hear relay click as you powered up? This probably means the LM324 is fine too.)

I'd look at the pins on RP7 (on your front panel) and ensure RP6 is still good (don't know where it is - trace the two RP7 pins that isn't the wiper, one of them supposedly leads to another potentiometer and then to GND. This leg is the suspect leg.

[orientalsniper]

Re: Bench PS Problem (Volteq HY3010D)

Yeah, I can hear the clicks when I power it on.

I can see where RP6 and RP7, how would I test them?

[eccerr0r]

Re: Bench PS Problem (Volteq HY3010D)

The wiper of RP7 should be the same voltage as what you see on pin 2 of M1.
The voltage at RP6 should be fairly low on both sides (one should be GND, other should be somewhat low). The pin that's connected to RP7 should of course be the same voltage as the higher of the RP6 voltages.

If RP6 voltages are high -> bad ground on RP6
If RP6 voltages low but RP7 voltage high - bad connection between the two potentiometers (or RP6 is broken).

If RP7 had been broken, you should be able to go both low and high but not stuck high... or maybe some random voltage on output if the wiper is bad. Perhaps it would be good if you take a 1MΩ resistor and connect the RP7 wiper(or pin 2 of M1) to GND to make it drop low if the wiper is intermittent or broken... Actually, the leakage of C13 should leak down to 0V if the wiper was bad, so your RP7 wiper is probably good.

[orientalsniper]

Re: Bench PS Problem (Volteq HY3010D)

Hello, by wiper you mean middle pin?

Ok, so in RP7: middle pin is 38V, another one is also 38V and last one is 0V (I assume it's GND) and in RP6: I'm getting 1.2V in one of the pins that is not in the middle, the other two are 0V.

[eccerr0r]

Re: Bench PS Problem (Volteq HY3010D)

Yes, middle pin is usually wiper, if it's a regular pot.

Okay, something doesn't make sense here. The 1.2V should be showing up on RP7 because RP6 is connected to RP7. Now the problem here: since the middle pin is 38V, that's exactly what the feedback loop is trying to match!

Question is, Why is it 38V? Is it stuck there? When you change the position of the potentiometer, it should change the voltage there... if not, that's the problem there.

The next unlikely possibility is if C9 is shorted. Which it can't be because it's not even populated and neither is C13. Wow they took a lot of shortcuts on this board to cheapen it...

[orientalsniper]

Re: Bench PS Problem (Volteq HY3010D)

I measured them again, getting different readings:

RP7:
-Pin 1: 38V
-Pin 2: 38V
-Pin 3: 1.5V

RP6:
-Pin 1: 0V
-Pin 2: 0V
-Pin 3: 1.5V

So I moved the knob and the voltage goes higher, from 38V to 50ish V, middle pin reflects the same voltage as in the display.

[eccerr0r]

Re: Bench PS Problem (Volteq HY3010D)

Which pin on RP7 goes higher? both 1 and 2 stay at the same voltage and together - this would be unusual behavior. Thinking about it, pin 1 should always be higher voltage than pin 2 until you hit the end of travel.

Is it difficult to disconnect the wiper pin (center pin) from its wire and ...

1. Connect the disconnected wire to GND through a 1K resistor (nominal, pick any value greater than say 400 ohms). What is the voltage on the output now?

2. What is the voltage at the center pin 2 (without the step 1 hack), does it vary between pin 1 and 3 as you adjust the control?

Currently thinking that the M1 µA741CN may truly be at fault now. The design of this PSU is very scary IMHO and could result in this IC's death... If you do end up replacing it, definitely socket it.

(sigh. I wish I had a use for the pile of LM741's in my junk box...)

[orientalsniper]

Re: Bench PS Problem (Volteq HY3010D)

Pin 1 and 2 of RP7 have 0 resistance between them.

1. Disconnecting the middle pin of the potentiometer (RP7) and with a 25K ohms resistor to GND, I'm getting around 51V.

2. Without any hack, moving the knob, pin 3 of RP7 goes from 1.9V to 1.5V (goes from high to low inversely to main voltage 38V to 50V).

I had already ordered the IC's of the N2 and N4 when I made the post, in case they are bad.

[eccerr0r]

Re: Bench PS Problem (Volteq HY3010D)

Whoops made a mistake on post 24, the middle/wiper of RP7 should be connected to pin 3 of M1 - as the schematic says, not pin 2.

Okay, based on this information, it seems M1 is bad - the input somehow is shorted against something inside the IC and passing voltage out instead of being high impedance. I would hesitate to swap M2 with M1 but if you want to try it, go ahead (or simply leave M2 out; it should still work without it - but without current limiting.)

I would think LM741s are cheap, perhaps you should have bought a tube (or perhaps whatever the first discount batch) of them

[orientalsniper]

Re: Bench PS Problem (Volteq HY3010D)

Hahaha, I bought a lot of 10 pieces, for now I will swap the IC's and report back.

What is your suggestion to protect the IC against the bad design of this PSU?

[eccerr0r]

Re: Bench PS Problem (Volteq HY3010D)

I think adding C13 in, as well as adding a resistor in series with the wire you disconnected may be the things you could do to help prevent damage to the IC. This mod will slow down the slew rate of the potentiometer.

A cheap/FREE solution would be to change how the operator uses the knobs - to not turn the knob (specifically RP7) rapidly If you make slower adjustments to the knob, not letting the knob voltage go way too out of sync with the voltage on the meter, it will help protect the IC. This is especially important if you connect additional capacitors outside the PSU.

Otherwise, make sure you have a good socket there, and replace them if it goes bad with the same symptoms again. Unfortunately this may mean you may be powering something with 50 volts. (What were you doing with the PSU when it broke?)

[orientalsniper]

Re: Bench PS Problem (Volteq HY3010D)

I just swapped the IC's, still got the same problem.

I didn't do anything, I use the power supply to find shorts in motherboards. I remember turning it on once and got this problem.

I found someone with a related problem: https://electronics.stackexchange.co...y-stuck-on-48v

[eccerr0r]

Re: Bench PS Problem (Volteq HY3010D)

With M1 disconnected/removed, can you adjust the voltage all the way to a low voltage on the middle pin of RP7? That needs to be ascertained before anything can be done...

Based on the other link, it seems that there are multiple problems that cause the LM741s to die, unfortunately it looks like you may have a few more dead LM741s...

Did you replace the LM324? Can you leave the LM324 out while debugging (or disconnect the coils to the relays)? This should help save the LM741s while debugging....

[orientalsniper]

Re: Bench PS Problem (Volteq HY3010D)

Before we go any further, which pin is 1 in the potentiometer? Maybe I'm measuring pin 3 as pin 1....

If you swap the measurements between pin 1 and pin 3, would the diagnosis change?

[eccerr0r]

Re: Bench PS Problem (Volteq HY3010D)

https://en.wikipedia.org/wiki/Potentiometer for a picture. I would label 1 2 3 as in order, and with these pictures, pin 2 is the middle one, and is connected to the wiper.

As pin 1 and 3 should be reverse-images of each other, knowing what the voltage of both are will tell what the range the middle one/wiper should be.

I normally would consider pin 1 will have 0 ohms (or close to 0 ohms) to pin 2 (wiper) when the knob is rotated all the way to the counter-clockwise direction. Likewise pin 2 would be 0 ohms to pin 3 when the knob is rotated in the clockwise direction. Hopefully this will kill some ambiguity at least in what I call what pin

The key numbers: pin 2 voltage needs to be between the voltages at 1 and 3. It could be equal, but only if rotated fully clockwise or counterclockwise.

[orientalsniper]

Re: Bench PS Problem (Volteq HY3010D)

I will have to read up on it.

So took out M1 (it's marked as N2 the same for M2) pin 1 (or 3?) and 2 are the same voltages, started out as 51.2V as lowerst, if I moved the knob to maximum it reached 51.8V.

[eccerr0r]

Re: Bench PS Problem (Volteq HY3010D)

If you have RP6 tuned all the way down to 0V, if you can't get RP7's wiper (pin 2) to 0V with M1 (or both LM741s) out of circuit, something is wrong with RP7.

I assume RP7 is coarse and RP6 is fine control on the front panel?

Also, just making sure we aren't chasing the wind here: Are you measuring the output with an external (at least somewhat calibrated) meter of some sort, and not reading the display on the PSU itself?

[orientalsniper]

Re: Bench PS Problem (Volteq HY3010D)

This is the power supply: http://www.volteq.com/volteq-regulat...new-model.html

RP6 is fine and RP7 is coarse.

Yeah, I'm using a Fluke multimeter to measure the voltage and it's the same as the display on the PSU.

[eccerr0r]

Re: Bench PS Problem (Volteq HY3010D)

Okay, I recall a thread we had on badcaps.net about someone else working with the display and we were having all sorts of trouble with it, so thanks for confirming that you're not trusting the readout

So can you adjust the wiper pin of RP7 (coarse) all the way down to 0V when the IC is out of socket, and you can't do it anymore when it is in socket? Doesn't point fingers, but wanted to verify that the resistors can indeed go down to 0V. This is assuming that the voltage on the output of the PSU is that unexpected voltage of >38V with the IC out of socket is still there.