replacing schottky diodes on a AV power supply

[DjKrish]

Re: replacing schottky diodes on a AV power supply

Tested the unit, everything works perfectly fine with the new original diodes.

[DjKrish]

Re: replacing schottky diodes on a AV power supply

Well, if you want to get an answer for that, or at least get a clue, do the test I suggested above with the old rectifiers and the power adapter. If they test bad, then we know. And if they don't, then they weren't the issue and probably something else happened that you didn't realize was happening.

Already tested, its just some cheap Chinese diodes thats not even accurate. Well, the luck was just not there. Ive returned back those diodes and request for originals.

[momaka]

Re: replacing schottky diodes on a AV power supply

Wonder why the rest didnt work? Hmmmm

Well, if you want to get an answer for that, or at least get a clue, do the test I suggested above with the old rectifiers and the power adapter. If they test bad, then we know. And if they don't, then they weren't the issue and probably something else happened that you didn't realize was happening.

[DjKrish]

Re: replacing schottky diodes on a AV power supply

Thanks guys for the inputs. Ive been away for quite a while now. And the parts arrived as well. Fitted in 2 pieces of sr320. Works perfectly. Wonder why the rest didnt work? Hmmmm

[momaka]

Re: replacing schottky diodes on a AV power supply

Why not test those SB340 diodes with power? IMO, no need to waste time and money looking for new diodes if you can't confirm the old one(s) is bad.

Take a 20V laptop adapter and something with a heating element that has about 10 Ohms resistance and connect it as a load on the laptop adapter through the diode. Then measure to see if the diode has proper voltage drop in the forward direction. After that, reverse the diode and test again. It should block current from going to the heating element. If you can confirm this, then your SB340 diode(s) are not bad and maybe there was another anomaly that happened at the time when you tested the PSU.

[stj]

Re: replacing schottky diodes on a AV power supply

just check any scrap psu's you have for a TO220 package schottky.

[budm]

Re: replacing schottky diodes on a AV power supply

Do you have any broken boards that you can find some similar diodes that you can try?

[DjKrish]

Re: replacing schottky diodes on a AV power supply

Fake? That i could suspect. The supplier said its a chinese company made. Sighs. Looks like i need to reorder a good quality ones again

[budm]

Re: replacing schottky diodes on a AV power supply

Bad or faked SR340?

[momaka]

Re: replacing schottky diodes on a AV power supply

this doesn't make any sense.

Agreed.

Either the SB340's were bad ad STJ suggested or connected backwards.
-OR MAYBE-
PSU had a hickup by coincidence when the SB340's were installed and somehow voltages were off only then.

Best way to know is to repeat the experiment. Better yet, test the SB340 diodes outside first - not just with a multimeter, but rather pass 12V DC through one and feed a dummy load. Then reverse the diode and try again. In the reverse direction, the diode should be blocking any current from flowing. If it's partially shorted (i.e. shorted with high resistance), it will pass current in both directions.

[stj]

Re: replacing schottky diodes on a AV power supply

maybe the 340's are bad

[CapLeaker]

Re: replacing schottky diodes on a AV power supply

SR340 - 5v plus
SR320 - 12v plus
B31V present

this doesn't make any sense. Did you install the other schottky backwards?

[DjKrish]

Re: replacing schottky diodes on a AV power supply

So when you install SR340 you say you no longer get the switched B12V?
When that happens, what Voltage do you get at the Cathode of SR340 with ref to circuit ground?
Is switched B31V present when that happen?
Can you also provide the full PDF of the service manual?

SR340 - 5v plus
SR320 - 12v plus
B31V present

[DjKrish]

Re: replacing schottky diodes on a AV power supply

Sorry, heres the PDF file

[DjKrish]

Re: replacing schottky diodes on a AV power supply

So when you install SR340 you say you no longer get the switched B12V?
When that happens, what Voltage do you get at the Cathode of SR340 with ref to circuit ground?
Is switched B31V present when that happen?
Can you also provide the full PDF of the service manual?

Heres the pdf file.

[budm]

Re: replacing schottky diodes on a AV power supply

So when you install SR340 you say you no longer get the switched B12V?
When that happens, what Voltage do you get at the Cathode of SR340 with ref to circuit ground?
Is switched B31V present when that happen?
Can you also provide the full PDF of the service manual?

[DjKrish]

Re: replacing schottky diodes on a AV power supply

This is the section. Output is 12V.

[momaka]

Re: replacing schottky diodes on a AV power supply

parallel diodes double the current, not the voltage

Theoretically that's correct.

However, if the diodes are not built on the same physical die (as is the case here, where O/P has two separate diodes wired in parallel on the PCB), then one diode will run hotter than the other. When that happens, the forward voltage of the hotter diode will drop further, making the the circuit "prefer" to push more current through that diode, which will in turn heat up the diode even more. If this continues, thermal runaway may eventually kill the diode if the circuit has the capacity to push a sufficiently large current through it.

Because of that, I agree with what STJ suggested: use a single 6 Amp (or higher) diode/rectifier (and preferably Schottky type for lower losses.)

both should be vf 0.55
https://cdn.badcaps-static.com/pdfs/...5f72338fd7.pdf

That's the maximum expected voltage drop at the rated current of the diode (3 Amps). Most multimeters push much much less than that when testing components (typically in the order of a few uA to maybe a fraction of a mA max.) As such, the Vf will appear much lower. Figure 3 in the above datasheet shows Vf for any given current from 0.1 Amps to rated surge current. You can see that for 0.1 Amps of current, the Vf is around 0.2V for SR320-340. So with a multimeter, the Vf should likely show even lower value... though depending on multimeter quality/design, that may not always be the case.

[stj]

Re: replacing schottky diodes on a AV power supply

that's at max current, they generally meter at about 0.18 on a meter

[petehall347]

Re: replacing schottky diodes on a AV power supply

both should be vf 0.55
https://cdn.badcaps-static.com/pdfs/...5f72338fd7.pdf