Soyo 24" stopped, help!

[freelander]

Re: Soyo 24" stopped, help!

I haven't ordered replacement diodes or zener diodes before and I'm not sure how to figure out which one I need just by looking at it. Any suggestions?

[freelander]

Re: Soyo 24" stopped, help!

I scraped off some of the glue to reveal the labelling for what I previous called transformers. BSFP24T1 is lavelled T1 so I am assuming that it is truly a transformer. BSFP24L1B is labelled L1 so I am assuming that it is an inductor. Either way, I don't think these components should have any opens so I think that they need to be replaced. I would love if someone could confirm my line of thinking.

I can't find replacements on digikey...any suggestions?

[Th3_uN1Qu3]

Re: Soyo 24" stopped, help!

If they're reading shorted, they probably ARE. But the only way to truly know is of course removing them from the board and testing them that way.

[freelander]

Re: Soyo 24" stopped, help!

There are a number of surface mount diodes and one zener diode (Top right corner but I don't really know the difference) that measure shorted when tested with the DMM diode function in circuit. I have circled them. There is one diode (circled in purple) that is a normal diode on the top side of the board that is reading shorted.

[freelander]

Re: Soyo 24" stopped, help!

The thermistor is measuring 3.7 Ohm at room temp. Diode D1 is good measuring .48 V in one direction only.

The picture shows a big brown thing that I can't identify in the picture. Point G is one side and D is the other. Point J is one lead of the resistor to the right of the big capacitor. Point H is the negative lead of the big capacitor.

[PlainBill]

Re: Soyo 24" stopped, help!

I double checked pins 1-2 and they are open loop to each other. Pins 1/4 and 2/5 are shorted in pairs out of circuit.

I noticed a little chunk broken away from the thermistor (?) early in the AC power circuit. I don't know what this does but could this be a problem?

That is a NTC thermistor. It's resistance decreases as it heats up. Measure thee resistance when it's cold; it should be something in the range of 10 - 50 ohms. If it's lower, it's shorted. I'd order a new one when buying parts.

PlainBill

[retiredcaps]

Re: Soyo 24" stopped, help!

Have a look at the following:

A to B = .1 Ohm
C to B = .1 Ohm
C to E = OL (1.03M Ohm)
C to D = .1 Ohm
E to F = .1 Ohm
E to G = .1 Ohm
E to H = .1 Ohm
E to J = .1 Ohm
For each letter above, what is the corresponding component?
A= one side of jumpers
B= the other side of three jumpers
C= pin 4 (positive) of bridge rectifier
E= pin 1 (negative) of bridge rectifier
F= leg of the heat sink
G,D,J,H= see picture for top side of board (note that I have edited the previous post so the burn marks and components aren't from my board)

I can't tell from the top picture what G,D,J,H are.

Okay, this may be a total red herring and my tracing could be wrong, but one way pin 1 and 4 of the bridge rectifier can be shorted in circuit and open out of circuit is if BSFP24L1B pin 1 and pin 2 are shorted. However, you have verified that BSFP24L1B pin 1 and pin 2 are open using a multimeter.

From tracing, another way is if diode 1 (D1) is bad. So test D1 in circuit with your diode check function on the multimeter. You should get 0.4 to 0.7 one way and 0L the other way.

I hope I'm not leading you down a wild goose chase here.

[freelander]

Re: Soyo 24" stopped, help!

Have a look at the following:

A to B = .1 Ohm
C to B = .1 Ohm
C to E = OL (1.03M Ohm)
C to D = .1 Ohm
E to F = .1 Ohm
E to G = .1 Ohm
E to H = .1 Ohm
E to J = .1 Ohm
For each letter above, what is the corresponding component?
A= one side of jumpers
B= the other side of three jumpers
C= pin 4 (positive) of bridge rectifier
E= pin 1 (negative) of bridge rectifier
F= leg of the heat sink
G,D,J,H= see picture for top side of board (note that I have edited the previous post so the burn marks and components aren't from my board)

[retiredcaps]

Re: Soyo 24" stopped, help!

I noticed a little chunk broken away from the thermistor (?) early in the AC power circuit. I don't know what this does but could this be a problem?

I don't know enough about that component to say yes or no. I'm sure someone else will chime in.

[retiredcaps]

Re: Soyo 24" stopped, help!

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

Okay, I marked up this diagram. Can you measure, record and report the following ohms (all in circuit)? Please record the actual ohm reading. If your multimeter is not autoranging, set it to 200 ohm setting.

A to B
C to B
C to E
C to D
E to F
E to G
E to H
E to J

For each letter above, what is the corresponding component?

I know that C and E are pins 1 and 4 of BSFP24L1B. What is

A, B, D, F, G, H, and J?

There is no letter "I".

edit: It could very well be that the design is to have pin 1 and 4 connected because you tested the rectifier out of circuit and found them all open. I'm just trying to trace this circuit to see where they connect.

[freelander]

Re: Soyo 24" stopped, help!

I double checked pins 1-2 and they are open loop to each other. Pins 1/4 and 2/5 are shorted in pairs out of circuit.

I noticed a little chunk broken away from the thermistor (?) early in the AC power circuit. I don't know what this does but could this be a problem?

[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?

[freelander]

Re: Soyo 24" stopped, help!

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

[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.

[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 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

[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?

[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!

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.

[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