Bench PS Problem (Volteq HY3010D)

[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)

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)

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)

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)

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)

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)

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)

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)

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)

Actually don't be hasty and replace them, we don't know what's wrong yet. If you report the voltages on those pins then we could help pinpoint the problem.

I tried to make a guesstimate based on the schematic. I referenced "Ground" as the negative output of the main power supply, just to pick an arbitrary point.

And yes, UA741CN, same op amp circuit as LM741.

[orientalsniper]

Re: Bench PS Problem (Volteq HY3010D)

Oh yeah, I just didn't need the PSU urgently and had things going on in life. I had the parts ordered months ago and just replaced them.

You mean UA741CN? You want the voltage to ground? I can't seem find ground in this PCB.

Edit: Just read your edit, I'm just going to order the UA741CN and LM324, will report back when I replace them.

[eccerr0r]

Re: Bench PS Problem (Volteq HY3010D)

Ah... problem still exists we thought you fixed or gave up!

Well M1 and M2 (LM741s) are the error amplifiers - M1 being the voltage error amplifier (M2 is the current limit feedback). What is the voltage at each of the pins of M1 when you have the voltage turned down all of the way?

In case it's not clear, M1 is the LM741 that has the unpopulated C8 near it and J7 on the other side. M2 is the one that's between C10 and RP9.

Oh gosh 45V??? I think that will kill the LM741, you may need to replace them regardless now. But still report the voltages an the pins. A proper working PSU probably should look like:

(Note: voltages reference to GND, or output negative pin)

Pin 8 - NC - ignore
Pin 7 - V+ 12V over what your output voltage is
Pin 6 - OUT your output voltage minus somewhere from ~3 to ~11 volts.
pin 5 - Offset - ignore
pin 4 - V- 12V under what your output voltage is
pin 3 - IN+ this should be fairly low, no more than 1V or so
pin 2 - IN- this should be whatever your output voltage is
pin 1 - Offset - ignore

[orientalsniper]

Re: Bench PS Problem (Volteq HY3010D)

OP rezzing thread, just replaced V14 and V13, still voltage high, 45V now.

[redwire]

Re: Bench PS Problem (Volteq HY3010D)

It's the usual circuit, where the pass-transistor (array) is normally on (R4, V11) and the control op-amps turn it off through an OR-gate (V15,V16).

Like budm mentions, check the driver transistors. I would check the +12V, -6.2V rails.

Circuit-common for the control op-amps and stuff is the power supply's +OUTPUT, once you get a handle on that, these chinese bench PSU's are easier to repair.
But like this one, a potpourri or kludge of parts.

[budm]

Re: Bench PS Problem (Volteq HY3010D)

So you verify that the Output transistor driver V13, V14 are good?

[orientalsniper]

Re: Bench PS Problem (Volteq HY3010D)

I just replaced the 4 power transistors (2N3055) and still got the same problem.

[stj]

Re: Bench PS Problem (Volteq HY3010D)

shit, that's some scary foto's!

the cap almost? touching the heatsdink, the rectifier just bolted to the case without sleeving on the outputs, the soldering!

[orientalsniper]

Re: Bench PS Problem (Volteq HY3010D)

I tested the 4 2N3055 in circuit and they don't appear to be shorted. I'm gonna have to desolder them and do this test ( https://www.youtube.com/watch?v=xyKzUCrwTpA ) to make sure.

I attached better and more focused pictures (log in to see) so you get an idea of what's inside.

[orientalsniper]

Re: Bench PS Problem (Volteq HY3010D)

Thank you all for the assist, I'm gonna try all your suggestions and will let you know.

[stj]

Re: Bench PS Problem (Volteq HY3010D)

http://www.volteq.com/volteq-regulat...new-model.html

looks like a rebadge of:
http://www.mastechpowersupplies.com/...h-hy3010d.html