Diode test results show reading both ways

[AcGeorgiegirl]

I've a diode in a tv psb that has a reading forward and bias. This is with it in circuit. Out of circuit, it tested normally. Any thoughts?

[budm]

Re: Diode test results show reading both ways

You need to trace out the connections to see if the diode is connected in parallel with other device or not.
Pictures of what you are testing?

[AcGeorgiegirl]

Re: Diode test results show reading both ways

Here's a pic of the psb on the tv I am working on. The diode in question is circled. Would it help if I took the same pic of the underside, to show tracings?

[ReeceyBurger123]

Re: Diode test results show reading both ways

What the fault with the Tv ?

[stj]

Re: Diode test results show reading both ways

CY2 ceramic, lower right corner!

[capwizard]

Re: Diode test results show reading both ways

eagle's eyesight ..................

[Longbow]

Re: Diode test results show reading both ways

Nope, you are looking at some of that grey adhesive, not a ruptured capacitor. Even so, if there were a problem right next to the main primary side rectifier bridge, do you think that it would cause a secondary rectifier to fail or read incorrectly? I think not.

The fastest way to check the diode is to desolder one leg and re-measure. It is probably a Schottkey and will measure somewhere around .2 volts forward.

[stj]

Re: Diode test results show reading both ways

it could cause anything with a 2pin power cord,
those are the caps coupling the mains to the groundplane!

[budm]

Re: Diode test results show reading both ways

Here's a pic of the psb on the tv I am working on. The diode in question is circled. Would it help if I took the same pic of the underside, to show tracings?

Does it show conduction in both direction if the white connector to the main board is not in place.
We do need good clean straight shot of the bottom side of the board too.

[budm]

Re: Diode test results show reading both ways

What the fault with the Tv ?

+1
History of the TV?

[ReeceyBurger123]

Re: Diode test results show reading both ways

+1
History of the TV?

We need to be taking a few more baby steps lol

[AcGeorgiegirl]

Re: Diode test results show reading both ways

What the fault with the Tv ?

Tv has no standby light or backlight/no image.

[budm]

Re: Diode test results show reading both ways

Post #9

[AcGeorgiegirl]

Re: Diode test results show reading both ways

Does it show conduction in both direction if the white connector to the main board is not in place.
We do need good clean straight shot of the bottom side of the board too.

It doesn't show conduction in both directions then. But, it does take a second to get to open OL, after cycling a few numbers around. Here's a pic of the back of the board.

[AcGeorgiegirl]

Re: Diode test results show reading both ways

We need to be taking a few more baby steps lol

The info below is another posting by me at https://www.badcaps.net/forum/showthread.php?t=59414

I started this posting because I didn't get a response about the diode issue there, and thought is was important....

There's no standby led lighting up. Without the main board connected, I get 5.14 on the 3 pins labeled for 5v for what I assume is standby(con isn't labeled as such...see pics). With main board connected, I get the following pin voltages:

1 gnd
2 5vcc 5.21
3 5vcc 5.21
4 gnd
5 5vcc 5.21
6 13vcc 12.71
7 13vcc_AUD 12.71
8 gnd
9 PWON 3.03
10 ACD 3.46
11 gnd
12 BLON 0
13 DIM 0

I realize that pins 6 & 7 are supposed to be 13v. I don't know what pins 9 & 10 should be, nor 12 & 13. Also, when checking diodes and fuses, I found that D210A on the Secondary side has reading both ways (208 and 1342) I keep running into this, and am wondering if this is normal on the secondary side, or not? I usually don't take the diodes out of circuit when I test them...maybe this is why I get this?

[CapLeaker]

Re: Diode test results show reading both ways

In plain English it sez:
The PSU has been turned on (pin 9 &10)
there backlight's are off (pin 12 &13)

So the BLon signal from the main board to the PSU to turn on the backlights is missing. Look at the mainboard and see if the if the BLon voltage is missing there too. If it is, you've got a main board problem.

[budm]

Re: Diode test results show reading both ways

It doesn't show conduction in both directions then. But, it does take a second to get to open OL, after cycling a few numbers around. Here's a pic of the back of the board.

OK, let me get this correctly, when testing the diode on board WITH all the connector in place, it shows resistance in BOTH direction, what is the resistance? Ohms, K Ohms?
Same test but WITHOUT other boards connected to the power supply board, resistance is???

[AcGeorgiegirl]

Re: Diode test results show reading both ways

OK, let me get this correctly, when testing the diode on board WITH all the connector in place, it shows resistance in BOTH direction, what is the resistance? Ohms, K Ohms?
Same test but WITHOUT other boards connected to the power supply board, resistance is???

Using diode mode on my DMM, the diode shows 204 and 1331 while the board is connected. Without connection, it shows 204 and OL. I'm sorry, I don't know what you mean by "Ohms, K Ohms"...well, I understand what Ohms are, in general, but not how I'd know numbers other than 204 and 1331. 204 is the forward bias and 1331 the reverse. Are you asking me to test resistance instead of in diode mode?

[AcGeorgiegirl]

Re: Diode test results show reading both ways

In plain English it sez:
The PSU has been turned on (pin 9 &10)
there backlight's are off (pin 12 &13)

So the BLon signal from the main board to the PSU to turn on the backlights is missing. Look at the mainboard and see if the if the BLon voltage is missing there too. If it is, you've got a main board problem.

Can you show me/tell me where this pin can be found? My board has nothing labeled.
I went ahead and followed the BLon pin wire from psb to main, and tested at the main side. It is still at 0, and so is the DIM pin.

[budm]

Re: Diode test results show reading both ways

Disregard.