I pulled a diode out of a PCB the is across pins 7 (anode) and 8 (cathode) of a PC923. It is shorted. So, the only markings on the diode are a big 3 4 small 7 . G. Basically 3 4 7 . G.

It looks like a standard black diode with the silver cathode band.

I just can't find this one. Any ideals? Thank you!

 

Post a pic. Also, what type of circuit function is it used in?

 

Are you sure it was a diode and not a decoupling capacitor as 8 and 7 are VCC and GND on the PC923? It could be a TVS though.

 

I will work on getting a pic. It is a diode. It measures .444 anode to cathode and open the other way. It is being used on a firing PCB for a servo drive. (Toshiba) Anode also ties into transformer. Cathode goes to pins 5 and 8 on PC923.

 

Here is a pic. I will try to get one with the numbers. Thank you.

 

Here is a decent pic. You can see the large 4 and small 7. To repeat is has a large 3 4 and small 7.G. Thank you.

Diode 3 4 7.G

 

Does look like a standard diode, possibly a 1N4007.

 

I pulled a diode out of a PCB the is across pins 7 (anode) and 8 (cathode) of a PC923. It is shorted.

The diode you show doesn't have 8 pins, only two. And a 0.444 reading one way is good and OPEN the other way is good. The diode is not shorted.

 

The diode you show doesn't have 8 pins, only two

No, the PC923 has 8 pins, see post #3

 

Your test shows that the diode is good.

If the anode us in the Gnd pin and cathode on Vcc it is reverse polarity protection.

 

I should have clarified. The one I measured is a good one from the board. The other one I pulled out is shorted. I just need a replacement for the failed one. Thanks.

 

can you post pictures of the board and where the shorted diode was? it may be rectifier, zener, schottky, fast recovery...
based on low values when tested in forward direction, it is probably Schottky. they are often used in SMPS for better efficiency.
the downside is lower breakdown voltage. pictures of board and other parts around it may help determining type

 

Per your request, here is a pic of the board. D5A is shorted. D1a, d3a, and d246a are the same as D5A. I was thinking about replacing it with a general diode such as a 1N4003 or 1N4007. Your thoughts? Thanks!

 

Cathode goes to pins 5 and 8 on PC923.

The cathode of diode D5A goes to PC923 (pins 5 & 8). see pic below

No, the PC923 has 8 pins, see post #3

See post #6

Here is a decent pic.

The PC923's have been removed.

Does look like a standard diode

Agreed. 1N4002 may be suitable. 1N4007 will very likely be suitable.

I should have clarified. The one I measured is a good one from the board. The other one I pulled out is shorted. I just need a replacement for the failed one. Thanks.

I'm assuming you're talking about D5A
View attachment 357266

 

View attachment 357268
Depending on the voltage feeding D5A any of the 1N's above will likely work. If you are feeding this board from 120VAC then 1N4003 would be minimal size to handle any possible reverse voltages. Since all seven of the diodes listed cost the same and are the same physical size, 1N4007 MIGHT be suitable. Since we don't know for sure exactly what you've removed we can't be certain the above diodes would work. There are different types of diodes. Schottky, Zener, Signal and general are all I can think of for types of diodes.

 

Final comment here: It could just be a dead diode (shorted or open - you said it's shorted). Or there could be something else on board that caused the diode to short. Haven't said this in a long time but "Fully diagnose the problem before throwing parts at it." You could be sending another diode to an early grave. Put the wrong diode in and it could send other parts of the PCB to the grave.

Do you have a board part number? Or a model number of the unit under repair?

 

Per your request, the PCB is a Toshiba P6580910G. It is out of an ISS BSD7-R0750. There were several components that were damaged. I'm repairing the PCB. All the parts have been identified with exception of the D5A. ie - transistor, caps, zener diode, resistor network, opto's, and shorted IC. This is the last part that I need. I appreciate everyone's input!!

Re: diode 3 4 7.G

 

many products have code instead of part number so it may be difficult or impossible to identify. i would focus on finding suitable substitute. but it is clear that D5A is not a zener or TVS - because of silkscreen marking (there is a zener next to it - ZD5A). btw the image you posted is not crisp and bottom size of the board is not shown.

pretty sure any standard rectifier diode will do (1N4001 - 1N4007) since this appear to work as rectifier for positive voltage of the PC923. the filter caps are large (330uF?) so voltage and frequency are low (as is current draw).
This is what datasheet shows, there is no battery. each PC923 gets (rectified) power from separate secondary from some transformer

 

I agree. I was in search of a suitable replacement as using 'google' came up empty. I'm sure the diode code is from the original manufacturer. I'm leaning towards a 1n4007. It should be beefy enough. I can post the bottom of the PCB if you think it would help. Again, thanks for everyone's input.

 

THAT BOARD HAS BEEN BURNED!
View attachment 357291
At this point it may be beyond repair. First you need to understand what caused it to burn up like that. Then you need to rectify that issue. Then you need to create jumpers to bypass the burned-out traces.

I should have noticed it before.