Power source with loud noise and does not work well (FDPS-100N-R5)

[SoporteHR]

Re: Power source with loud noise and does not work well (FDPS-100N-R5)

that is common everywhere,
i only repair stuff i get for free first or stuff that cant be replaced because it's special or expensive.
the usual stuff - tv's pc's etc people just dump and replace.

Yes, until last year it was profitable to repair that kind of equipment, now it's time to redefine the business focus to look for more profitable things.

Thank you

[stj]

Re: Power source with loud noise and does not work well (FDPS-100N-R5)

now in Venezuela, the cost of repairing has exceeded the cost of purchasing a new unit

that is common everywhere,
i only repair stuff i get for free first or stuff that cant be replaced because it's special or expensive.
the usual stuff - tv's pc's etc people just dump and replace.

[SoporteHR]

Re: Power source with loud noise and does not work well (FDPS-100N-R5)

Hello STj, thanks for the info, if you knew that change of name from Lucky GoldStar to LG.

Momaka, thanks for your comments, it was a challenge and it helped me to solve it was when I decided to change IC1. After that the source began to work perfectly and zero noise.

The components as you comment, use them from a PSU ATX that had no use.

It's a pity that the client found the repair very expensive, now in Venezuela, the cost of repairing has exceeded the cost of purchasing a new unit.

Finally one of the primary capacitors of 250v x 220uf does not indicate reading with the tester or with the ESR meter that I built. Then the total of components to change is 17.

So, I only had the experience and learning. (which is important)

Thank you all.

[momaka]

Re: Power source with loud noise and does not work well (FDPS-100N-R5)

Ah, I missed the replies.

Good to hear you got the PSU fixed, though. (And all by your own troubleshooting work too. )

Removed IC1 to check for pins in short circuit and found the following.

Tester in function Diode test / continuity

Pin 7 (GND) with Pin 13 (Output Control) = 0,32ohm
Pin 7 with pins 10 (E2) and 11 (C2) = 0.10 ohm
Pin 7 with pin 1 = 617 ohm
Pin 7 with pin 2 = 617 ohm
Pin 2 with pin 13 = 632ohm
Pin 3 with pin 11 = 615ohm
Pin 7 with pin 4 = 625 ohm
Pin 4 with pin 11 = 625ohm
Pin 5 with pin 6 = 753 ohm
Pin 7 with pin 5 = 592 ohm
Pin 12 (VCC) no reading regarding the other pins

I'm surprised no one saw these readings as problematic, particularly the short-circuit between C2 and E2. In fact, this is most likely causing the buzzing you heard and the reason for the partial voltage. After all, pins 10/11 are used for the output drive, along with pins 8 and 9 (C1 and E1). In a half-bridge PSU, all of these are used. But with C2 and E2 being shorted, one of the transistors on the primary side will never be driven to turn On... and hence why the PSU couldn't come up to full output voltage.

All the other readings are problematic too, as some pins are pretty much heavily insulated from each other.

I removed the IC TL494 and replaced it with another that I extracted as a test of an ATX PSU. Immediately the source stopped ringing and the voltage on the PIN 12 stabilized at 17.55vdc and on pins 13 and 14 I got the reference voltage of 4.94 vdc. (5vdc nominal)

So this was the whole problem, the failure of the IC affects the operation of both the primary and the secondary.

Now it's time to locate the new replacement components, since it uses pieces extracted from other equipment as a test.

It should be fairly easy to find a replacement IC like that. Just about every older cheaper/gutless/crap half-bridge ATX PSU has it. So just go around a few computer shops and ask if they have old broken AT/ATX PSUs.

As for the IC itself (TL494)... you can actually use any of the following:
DBL494
KA7500

The KA7500 is basically pin-compatible replacement for the 494. That said, some very old socket 462 motherboards also used a 494/7500 chip for the CPU VRM (mostly cheaper ones like ECS and PC-chips). If you have a dead one from that era, have a look. It may just have this IC.

[stj]

Re: Power source with loud noise and does not work well (FDPS-100N-R5)

LG = Goldstar.
the original comany name back when i was buying 5¼ floppy disks from them was "Lucky Goldstar"
so now you know what "LG" stands for!

[SoporteHR]

Re: Power source with loud noise and does not work well (FDPS-100N-R5)

Hi R_J

What a coincidence, if the screen really turns on all the decimal points of the display or shows very fast erratic readings.

So nothing, impossible to measure anything with it in the primary.

Thank you all for your comments.

Greetings.

[R_J]

Re: Power source with loud noise and does not work well (FDPS-100N-R5)

I just had a closer look at your Goldstar DM-311 meter and it is the same as the LG DM-311 I have on the bench. They just don't like checking dc if there is a high frequency pulse also present like in smps and and ysus boards.

[CapLeaker]

Re: Power source with loud noise and does not work well (FDPS-100N-R5)

Happy you solved this problem. Usually IC's either work, or they don't. I guess in this rare case, the IC was at fault. There was nothing much more left to check on that board.

[R_J]

Re: Power source with loud noise and does not work well (FDPS-100N-R5)

Good to here you found the problem, Some meters do not like the high frequency pulses, that is likely why your meter has problems measuring the primary voltages.
I have an LG meter that goes overload when checking the Vs voltage on some plasma tv's (fluke checks them ok)

[SoporteHR]

Re: Power source with loud noise and does not work well (FDPS-100N-R5) Case Closed

Hi all.

Finally, I managed to find the problem of noise at the source (RrRRRRrrrrr) and the poor voltage output on the secondary.

I removed the IC TL494 and replaced it with another that I extracted as a test of an ATX PSU. Immediately the source stopped ringing and the voltage on the PIN 12 stabilized at 17.55vdc and on pins 13 and 14 I got the reference voltage of 4.94 vdc. (5vdc nominal)

So this was the whole problem, the failure of the IC affects the operation of both the primary and the secondary.

Now it's time to locate the new replacement components, since it uses pieces extracted from other equipment as a test.

Attached for future reference, image with the voltages measured when the source is operating correctly.

It was impossible for me to measure the voltage on the primary pins of T2, the multimeter goes crazy.

Thank you all for the comments and help provided

Case closed.

[RJARRRPCGP]

Re: Power source with loud noise and does not work well (FDPS-100N-R5)

220v and only see half the required voltage.

220V=If an old transformer, IIRC, when we used to only be 110V.

These days, 110V is considered a brownout, L O L

Chronologically, it likely went like this in the U.S.:

110,115,117,120

------------------------------------

With the pre-120V-rated ones likely being transformers that contained PCBs, if not also from the still-leaded gasoline and still-leaded paint era...

Even though, GMP seems to consider 123-125V defacto. Even when I once thought that they're possibly changing it to 127V.

[stj]

Re: Power source with loud noise and does not work well (FDPS-100N-R5)

o.k.

[SoporteHR]

Re: Power source with loud noise and does not work well (FDPS-100N-R5)

Hi, STJ,

That Switch was one of the first that I checked, because of the corrosion I saw, so I made a bridge with tin in its pins.

[stj]

Re: Power source with loud noise and does not work well (FDPS-100N-R5)

if the switch is bad it will expect 220v and only see half the required voltage.

[SoporteHR]

Re: Power source with loud noise and does not work well (FDPS-100N-R5)

Hi all.

Make the change of small capacitors, C11 and C10 did nothing. regarding the sound or voltage failure in the secondary of T2.

C13 and C17, C18, did nothing either.

When I changed C9, I already got a voltage of 16 vdc first, then low and stabilized at 7.6vdc.

Replace C22, ceramic condenser, since I saw it darkened.

However, on pin 12 of IC1 I have no tension.

I attach images of the tensions that I am already getting. and the video with the sound generated by the PSU before the change of capacitors.

The output of T2 I already have 7vdc.

Replace C5 and C6, original 220uf x 250v, replacement 330uf x 200vdc. (line voltage 110vac).
Probe C6 with the tester (Diode function) and did not load.

The noise became faster and sharper. but it was not removed.

The output voltage at the source went up to 14 vdc

Removed IC1 to check for pins in short circuit and found the following.

Tester in function Diode test / continuity

Pin 7 (GND) with Pin 13 (Output Control) = 0,32ohm
Pin 7 with pins 10 (E2) and 11 (C2) = 0.10 ohm
Pin 7 with pin 1 = 617 ohm
Pin 7 with pin 2 = 617 ohm
Pin 2 with pin 13 = 632ohm
Pin 3 with pin 11 = 615ohm
Pin 7 with pin 4 = 625 ohm
Pin 4 with pin 11 = 625ohm
Pin 5 with pin 6 = 753 ohm
Pin 7 with pin 5 = 592 ohm
Pin 12 (VCC) no reading regarding the other pins

I do not have that replacement IC to change or test.

Thank you.

[SoporteHR]

Re: Power source with loud noise and does not work well (FDPS-100N-R5)

Thanks for schematics R_J

[SoporteHR]

Re: Power source with loud noise and does not work well (FDPS-100N-R5)

Thanks for your answers, today I will try replacing all the small electrolytic capacitors.

If I thought the series was the problem, so I connected it directly to the 110vac line, the noise persisted.

I will notify you of the results.

[momaka]

Re: Power source with loud noise and does not work well (FDPS-100N-R5)

I connect the source and it starts but the transformer T1 starts zoning as if it had a relet inside (RRRRRrrrrrRRRRrrrrRRR)

Is that still with the 100W light bulb connected or not?

If it is with the 100W light bulb, then add another 100W bulb in parallel to it. Some PSUs simply don't like to have a light bulb on the input and might oscillate like that.

Also, check/replace all the small electrolytic caps, as the others have suggested.

[stj]

Re: Power source with loud noise and does not work well (FDPS-100N-R5)

check the voltage switch - that's a lot of corrosion on it!

[CapLeaker]

Re: Power source with loud noise and does not work well (FDPS-100N-R5)

look at these little capacitors that are close to a heat source (where the circuit boart turned color to brown). Probably that PSU could stand to have all of the 6 little caps changed.