Bench PS Problem (Volteq HY3010D)

[orientalsniper]

Re: Bench PS Problem (Volteq HY3010D)

For post #58

PS (-) with MM (-):

With RP7 wiper disconnected and MM (+) on it I could get from 18V to 37V by turning the potentiometer from one side to the other.

[orientalsniper]

Re: Bench PS Problem (Volteq HY3010D)

For post #52

PS (+) with MM (-):

Pin 4 of N4: 12V
Pin 8 of M1 and M2: 0V
Pin 11 of N4: -15V
Pin 4 of M1 and M2: -6.2V

R2: -6.2V and -27.8V
R39: 0V and -27.8V

[orientalsniper]

Re: Bench PS Problem (Volteq HY3010D)

I screwed up, wiper was grounded, check photo.

Tests done for post #51

Voltage measurements for M1 with M2 pulled out. PS (+) with MM (-):
-6.2
0
0
-6.2
-6.2
-0.5 (jumps a lot)
12
0

I will report back with the tests that follow.


EDIT: THERE WAS A BLOB OF SOLDER UNDER M2, MESSED UP THE READINGS.

[eccerr0r]

Re: Bench PS Problem (Volteq HY3010D)

Well, the worry is not necessarily something blowing up, it's damage to the potentiometers, they are not meant to handle that much power and well, kind of expensive to replace!

[orientalsniper]

Re: Bench PS Problem (Volteq HY3010D)

Yeah, I was a bit hesitant to leave the PS on for long period of time since I saw glue smoking off. Don't want a PS blowing up in my face.

I will double check tomorrow, I might have left RP7 wiper shorted to GND. I think I'm gonna put some safety glasses on.

[eccerr0r]

Re: Bench PS Problem (Volteq HY3010D)

This is weird. What's the output voltage of the PSU now? Oh gosh... that's also unexpected R16 overheating... hmm. need to check my other computer to think about what's going on with it now. At least you had a picture of the resistor before it heated up!

But anyway, what is the voltage on the output of the PSU now with that bottom LM741 out (Note that both of them are silkscreened N2, so be careful. I think you got the "right" one in terms of the voltage feedback unit versus the current feedback unit.)? If it's not 0V, could you do that short test on V13 - solder a wire between base and emitter of the transistor and check the voltage output real quick when turning it on.

In theory the output should be and remain at 0 on the panel, and all the relays should also be off - and thus that N3 regulator as well as pretty much all the semiconductors should also stay cool.

---

OH FSCK THAT'S WHERE R16 was... this is that resistor on top of the stack and it was a 47 ohm resistor which does NOT match the schematic with a 56Ω resistor.

*** DONT TURN THE PSU ON UNTIL YOU FIGURE OUT WHAT'S GOING ON!!! ***

This means the potentiometers are also passing a lot of current - in which they should NOT. Did you inadvertently short RP7's center pin/wiper that's normally connected to pin3 of the LM741 you removed, to GND? (or pin 4?). That could cause RP2 to fry if RP7 is turned all the way up... DANGER DANGER DANGER!

[orientalsniper]

Re: Bench PS Problem (Volteq HY3010D)

I think it's a new symptom since I took out M2 IC unless I haven't noticed it before because the glue near the heatsink is melting.

Check the attached photo please. Is R16 looking fine? It's got 0.433K ohms

I'm worried leaving it on for more than 15 seconds to do the other tests.

[eccerr0r]

Re: Bench PS Problem (Volteq HY3010D)

Well, other than drawing a lot of current, think it's doing fine. It only needs to draw 0.5A or so to get quite warm, with three relays all 'on' it can get there...

As long as it's not hot "OUCH" to the touch...

[orientalsniper]

Re: Bench PS Problem (Volteq HY3010D)

Yeah. 25V-0V-12V for the 3 pins. Heatsink is very hot, is it normal?

[eccerr0r]

Re: Bench PS Problem (Volteq HY3010D)

Has it always been getting warm? Is this a new symptom?

Is it still giving 12V out (measure its output with your black meter lead on the POS output of the PSU)?

This regulator would dissipate the most power if all three relays are on.

[orientalsniper]

Re: Bench PS Problem (Volteq HY3010D)

I'm overwhelmed, I was about to try post #51

Removed M2, put M1 back in and then turned on power supply, then I noticed N3 (L7812CV) giving off a lot of heat, it wasn't smoke, I'm pretty sure it was burning the glue in the heatsink.

[eccerr0r]

Re: Bench PS Problem (Volteq HY3010D)

Well, it was suggested the black input on the POSITIVE output of the power supply. But it really doesn't matter - as long as if you tell us where both probes are connected, then we can figure out the status of the supply.

The current outstanding tests/experiments are:
1. Still not certain about this: with the M1 µA741CN removed or the wiper/center pin disconnected from RP7, and RP6 set to the lowest setting: can you adjust the voltage on that center RP7 potentiometer pin through the whole range by turning RP7? Ideally, volt meter negative pin on PSU negative output as reference.

If result: pin2 of the potentiometer can now go through a large swing of voltages and even hit 0V. Then likely M1 LM741 is indeed shorted and the potentiometers are fine.
If result: pin2 is stuck at a few voltages and cannot swing more than a few volts. Then need to repair/replace potentiometers.

2. The two shorting experiments: either
a) Can you short V13 transistor's B to E (tests pass transistor tree for shut of capability)
or
b) short the anode of V16 to one of these three points: (tests shut off capability in general)
- pin 4 of M1
- pin 4 of M2
- anode of V6

If result: Voltage on the +PSU output will drop to 0 or at least very low.
Provided the diodes are good, this would strongly indicate M1 needing to be replaced if it's the only problem.
If result Voltage on the +PSU output stays the same.
This means one of the pass transistors have shorted or stuck on for whatever reason.

Oh boy just noticed V16 is an unpop too... need to see how the heck this thing is connected. Wow...

[orientalsniper]

Re: Bench PS Problem (Volteq HY3010D)

Hey, thanks for the replies and sorry for the delay, I need to fix some laptops first, need to clear my desk.

So for all my tests I have to use (+) lead of multimeter on (-) output of power supply? Got it! Will do the tests by the end of the day.

[eccerr0r]

Re: Bench PS Problem (Volteq HY3010D)

Any further words on the experiments while waiting for parts?

[eccerr0r]

Re: Bench PS Problem (Volteq HY3010D)

Staring at the schematic I still don't get how it can maintain regulation... VREF is ~2.5V over whatever the current output voltage is... So it appears to be comparing VOUT with (VOUT + 2.5)*(Frac*RP7+RP6)/(R16+RP2+RP6+RP7) or something like that. whiskey tango foxtrot, how stable can this be or am I missing something here?

Someone needs to give me one of these pieces of crap so I can play with it!

[redwire]

Re: Bench PS Problem (Volteq HY3010D)

Yes - the PSU can keep blowing the voltage control op-amp until some protective resistance and clamp diodes added, or the stuck output is fixed.

If OP's LM741 (M1) shorted, it can damage the voltage setpoint potentiometer or voltage divider trimpots. I would check RV7.

I add a pair of 1N4148's across the op-amp +/- inputs and a couple series 10k, one on each op-amp input.
Another protection diode across C-E of the pass transistors is needed but that is another discussion, if you ever charge batteries.

I would re-test the pass transistors and drivers. Shorting E-B on driver V13 should give zero output voltage.

Another weirdness about these power supplies is the voltage control pot/divider string goes from VREF to VOUT(-), it's not intuitive.

[eccerr0r]

Re: Bench PS Problem (Volteq HY3010D)

O/P has already verified the auxiliary PSU is working by the measurements done on M1 and M2 in #21.

Using PSU out+ as a reference is also reasonable, but really it doesn't matter where your reference is as long as you know what it is. Subtract out the 38V that's on pin 2 as this is connected to out+ from the voltages #21 gives the expected voltages based on the voltages listed...except that pin 2 should be changeable from 0 to ??? volts - indicating either a shorted/destroyed input caused by fast voltage change downwards, or the pot is broken somehow.

---

Another possible mod is to put a resistor in pin 3's path, and use two inverse series 5.1V zener diodes to clamp the input to pin 2. Actually, maybe don't even need zener diodes - two inverse parallel silicon diodes (or even LEDs) should technically do the trick too - just need to make sure that resistor is there to soak up the current that would flow through these diodes. This should be sufficient prevent the slew from damaging the LM741.

[kaboom]

Re: Bench PS Problem (Volteq HY3010D)

check 3 opamp supplies, using out + for DMM negative lead:

+12V at pin 8 of M1 & M2, pin 4 of M4
-15V at pin 11 of M4
- 6.2V at pin 4 of M1 & M2

also check at junction of R2:V6 and R39:V21

you must use out + as the common reference- see schematic

we cannot assume anything about the opamps til it's understood they've got both their pos and neg supplies.

[redwire]

Re: Bench PS Problem (Volteq HY3010D)

Use the power supply (+) output as your common point [multimeter (-)] for making voltage measurements on the control circuit.
Do not use the power supply (-) output as multimeter (-) it will drive you nuts.

The 2N3055 pass transistors and drivers V13, V14 are normally full on.
R4 and zener V11 bias them on, and the voltage M1/current M2 control op-amps turn the transistors OFF.
So both out-of-socket, the transistors will stay full on.

I would pull M2 (disable current control) and leave M1 in and measure voltages on all its 8 pins, WRT output(+).

A problem with these power supplies is the O/P goes straight into the op-amp M1- which leaves it vulnerable. The op-amp gets damaged if the PSU output gets stuck on, with RP7 set to minimum.
So it will continue to eat op-amps.

I have this schematic for a HY-3010D.

[eccerr0r]

Re: Bench PS Problem (Volteq HY3010D)

Ah okay... I can't be certain that the swap also killed the other 741 if it had been working, hence asking the 324 be removed in order to protect the 741 - and so that we can do some experiments. The 324 is used to save power.

I was wondering if you had sockets so removing the ICs and plugging them back in would be easier when the new ones arrive. Especially the M1 741: this one I can see it failing often.

Okay that's good that you can fairly easily desolder these ICs without damage to the board. At least this board is a single sided, which makes things easier.

Looking at the data for the LM741 you should be able to short the M1 output (pin6) to one of the rails (say, pin 4 for the test I am curious in) to see if the voltage on the PSU output will drop to zero without damage to the IC. I'd like to see this experiment done. If you can do this with M1 out of circuit, that would be okay too, then again I would hope the voltage output should be 0 with M1 removed. You can also short the anode (the non-banded side) of diode V16 to M1's pin 4 if you'd like instead, both of these theoretically should drop the PSU output voltage to 0.

All things are still pointing at the pots and/or M1 though.