Soyo 24" stopped, help!

[Pyr0Beast]

Re: Soyo 24" stopped, help!

This diode (on top) is the part of the snubber circuit it seems. Its failure will lead to failure of the switching fet.

Heatsinks are not meant to have their fets/diodes unscrewed from there. You have to desolder everything. Much easier.

Main cap also failed which in turn heats the transformer like crazy.

[Pyr0Beast]

Re: Soyo 24" stopped, help!

Soldering gun is too messy for that job. Buy a good soldering iron if you are planning to do more repairs. Good starts in the range of 100$+

Bad equipment will leave someone with no experience very frustrated. A pro can make good results with bad equipment, a newbie with bad equipment is a disaster.

You need good solder to do the job. Plumbing solder is for different purpose. While it does work it is not fit for any electronics. It is too thick and its flux is useless.

Buying cheap will not do the job. That money is better thrown away then.

//
This MAY be a difficult job. The ID10T who decided to put the caps under the heat sinks should have his hemorrhoids cauterized with a hot soldering iron. Maybe then he would be able to remove his head from his a**.//
It was done to reduce the ESR of the capacitors. Meaning they can put cheaper parts there. (Once it warms up it will mostly work fine, but cold-booting is the problem)

[Krankshaft]

Re: Soyo 24" stopped, help!

Look what I found.

"Soyo Group filed for Chapter 7 bankruptcy with the United States District Court for the Central District of California, Riverside Division (case number 09-19355-RN), and ceased operations on May 5, 2009."

I guess in the end they stooped to rebrands good riddance I say.

I'd replace that charred diode look at it's neighbor if it's unreadable.

That burn mark over the zener is probably a part of that Topswitch PWM / FET IC circuit for the standby supply.

[inaliz]

Re: Soyo 24" stopped, help!

Meaning they can put cheaper parts there. (Once it warms up it will mostly work fine, but cold-booting is the problem)

Thats when my monitor started acting up after a week of being idle. This seems to be getting very complicated. By chance does anyone know what a lcd repair shop might charge to remedy this?

[PlainBill]

Re: Soyo 24" stopped, help!

Thats when my monitor started acting up after a week of being idle. This seems to be getting very complicated. By chance does anyone know what a lcd repair shop might charge to remedy this?

It depends on how honest they are. An honest shop would tell you up front to buy a new monitor; they couldn't get a replacement board. A less than honest shop would charge you $50 - $100 to look at it and tell you that they couldn't fix it. If you handed it to me I would ask a minimum of $30 for the labor, plus parts. At that, I'd be cheating myself.

All of that doesn't really matter. It shouldn't be too hard to figure out what to use to replace the diode. It's unlikely the inductor is bad, but if it is finding a replacement shouldn't be too hard. Soldering in the replacements is no more difficult than replacing the caps - easier as a matter of fact (unless you try holing it in place while soldering it.)

The first step is a picture of the top of the board so I can see if any component identifier is visible and a picture of the bottom of the board in that area to evaluate the solder. They don't have to be close-ups, the same scale as the pictures where I numbered the caps is fine.

PlainBill

[freelander]

Re: Soyo 24" stopped, help!

I picked up one of these monitors cheap and upon visual inspection of the capacitors, they look good but the very first fuse on incoming AC power is open. Is it fair to assume that this fuse would normally blow on a surge and all else may be good? I really don't want to fight with removing the heat sinks to get access to the components if I don't have to.

[PlainBill]

Re: Soyo 24" stopped, help!

I picked up one of these monitors cheap and upon visual inspection of the capacitors, they look good but the very first fuse on incoming AC power is open. Is it fair to assume that this fuse would normally blow on a surge and all else may be good? I really don't want to fight with removing the heat sinks to get access to the components if I don't have to.

That is not a safe assumption. It is likely either the input rectifier or the main power FET is shorted. The input rectifier is the black rectangular 'box' attached to the heat sink just to the left of the power input socket in the first picture in this thread. You can check it for shorts from the bottom of the board.

If I were in your position I would replace every electrolytic cap in the power supply (including the 450 volt one) with new Panasonic FM or other high reliability brands. At a minimum, I would test the ESR on every cap. Again, if it became necessary to remove a heat sink, I would replace all the caps under that heat sink. This design is asinine.

PlainBill

[freelander]

Re: Soyo 24" stopped, help!

Thanks Bill...I wasn't sure shich box you meant so I edited a picture of the board of the device that I tested (in circuit) and all pins are shorted to each other which would seem to me that it is blown. Can you guide me to the other item to check? Note that the 3 legged transistor on the other side of the heat sink also has all legs shorted to each other (in circuit).

[freelander]

Re: Soyo 24" stopped, help!

oops...I missed the picture

[retiredcaps]

Re: Soyo 24" stopped, help!

Can you guide me to the other item to check?

If the other item is measuring the caps for ESR, you have to unsolder all the caps and use an ESR meter to measure them. You can't measure it with your multimeter.

An ESR costs anywhere between $40 to $300. Replacing all your caps will cost less than $10.

[freelander]

Re: Soyo 24" stopped, help!

Thanks...I'm pretty well versed in checking and changing capacitors but I just don't have much experience with the solid state devices so that throws me for a bit of a loop.

[PlainBill]

Re: Soyo 24" stopped, help!

Thanks Bill...I wasn't sure shich box you meant so I edited a picture of the board of the device that I tested (in circuit) and all pins are shorted to each other which would seem to me that it is blown. Can you guide me to the other item to check? Note that the 3 legged transistor on the other side of the heat sink also has all legs shorted to each other (in circuit).

Excuse me, I don't know your experience level. Those results are a little unusual. Let's verify them.

I would start by unsoldering the bridge rectifier and testing it out of circuit. Using a DMM set on a low (200 ohm) range, all pins should read open to one another. If ANY of them read less than 100 ohms it is indeed shorted.

Next check the power FET in circuit, but on the same 200 ohm scale. Some readings may change as the large cap is charged, but they should all show greater than 100 ohms when they stabilize.

If they are both bad you have a problem. This is a complex power supply, with a PFC front end, and standby and main supplies. And you (presumably) don't know how it failed. One ugly scenario is that it baked the capacitors until the surge currents took out the power FET, which took out the bridge rectifier, and then the fuse. An even worse scenario is that a power surge (lightning hit) was responsible. This MIGHT be a simple fix - replace the fuse, bridge rectifier, and power FET and you have a working monitor. Or a closer examination may show a few bulging caps, so you go ahead and replace the lot. If after spending $25 for parts and a few hours replacing them you wind up with good 24" monitor you will feel real good about yourself. However, I'm not fully confident about the FET shorts, takes out bridge, takes out fuse scenario.

PlainBill

[freelander]

Re: Soyo 24" stopped, help!

I am assuming that the power FET is the 3 leg one by itself on the heat sink. I will check back when I have tested it in circuit. For the time being, I desoldered the Bridge Rectifier and all legs are open loop to each other. I'm not sure if the results are different because of the user or because it is out of circuit! When I get it soldered in, I will test the 3 leg FET in circuit under power.

[Krankshaft]

Re: Soyo 24" stopped, help!

Whoa you don't want to do that! The only live checks you could do on a FET are voltage measurements.

Voltage drop checks are done with the power OFF.

To test the FET use the diode check function of the DMM. From gate to source reverse the probes then from gate to drain reverse the probes you should only get a reading in one direction on each test.

A blown main fuse almost always signifies a shorted component on the primary side of the supply. Unless you were hit by a surge but assuming that every time a fuse has blown will only cause you to waste fuses. While some surges just pop the fuse and the PSU is fine others can destroy primary side components. So it's better to check for shorted components before replacing a fuse.

[freelander]

Re: Soyo 24" stopped, help!

Krankshaft, clearly I misunderstood something and I wasn't doing something correctly before When I test the 3 legged FET (pointed out in the picture) I now don't have any shorts (I think I had the range wrong on my DMM). With the rectifier soldered back in, I have a short between the 1 and 4 pins. Does that mean anything in circuit?

[freelander]

Re: Soyo 24" stopped, help!

I have resoldered a number of things and put a quick blow fuse in which blows as soon as power is applied. Now...how do I track down the short?

I checked the two transformers (UU16-15mH) out of circuit and there doesn't seem to be any shorts.

Here are my results (tested out of circuit) on BSFP24L1B. Using the numbering that I applied, the following is the continuity that I get:
1-4 connected
2-5 connected
3 open loop to all other pins
6 open loop to all other pins
7 open loop to all other pins
8 open loop to all other pins

Here are my results (tested out of circuit) on BSFP24T1. Using the numbering that I applied, the following is the continuity that I get:
1-2 connected
3-4 connected
5-6 connected
7 open loop to all other pins
8-9-11 connected
10 open loop to all other pins
12 open loop to all other pins
7 open loop to all other pins
8 open loop to all other pins

[retiredcaps]

Re: Soyo 24" stopped, help!

With the rectifier soldered back in, I have a short between the 1 and 4 pins. Does that mean anything in circuit?

Can I see a clear focused picture closeup of the underside (solder side) of the area where the bridge rectifier is?

[freelander]

Re: Soyo 24" stopped, help!

I was editing pictures from the previous post. I have attached pictures of my actual board. I de-soldered and re-soldered the bridge rectifier for the test that PlainBill suggested. The bridge rectifier is the 4 vertical solder joints that are together.

Note that the fuse and the two transformers mentioned previously are out of circuit right now.

[freelander]

Re: Soyo 24" stopped, help!

Since removing the different transformers, I no longer have a short between the two pins mentioned in circuit.

[retiredcaps]

Re: Soyo 24" stopped, help!

Since removing the different transformers, I no longer have a short between the two pins mentioned in circuit.

I'm just trying to trace out the path between pin 1 and pin 4 on your bridge rectififer. I may have a marked up diagram for you to test for continuity after I study your pictures.

Can you re-measure pin 1 to pin 2 on the BSFP24L1B (out of circuit)? What ohms reading do you get?