BC796D: 796D Diode part # needed

[MadMapper]

Hello can anyone tell me what the part number is for the diode located between the power input and the ext. sp output. And the part number for the one at the corner were the trace turns? I was given a scanner and that diode is fried beyond recognition.

 

[nosig55]

You might dig around here: Radio Shack PRO-197 Service Manual (Page 16 of 75) | ManualsLib

 

[nosig55]

The schematic here: Schematic Diagram - Radio Shack PRO-197 Service Manual [Page 73] | ManualsLib

 

[MadMapper]

shoot i put the wrong model up. It's actually a Uniden BC796D

 

[tvengr]

Before replacing the diode, i suggest that you check the other diodes for being shorted or possibly a shorted electrolytic filter capacitor on the output of the power supply. Another high power component may have shorted to cause that much damage to the diode and circuit board. In any case, check for a short on the power supply bus before applying power to the scanner.

 

[MadMapper]

Before replacing the diode, i suggest that you check the other diodes for being shorted or possibly a shorted electrolytic filter capacitor on the output of the power supply. Another high power component may have shorted to cause that much damage to the diode and circuit board. In any case, check for a short on the power supply bus before applying power to the scanner.

the woman that gave it to me said she wasn't paying attention, and when she plugged it into a power strip, 1 prong went into 1 plug, and the other prong into a second plug

 

[tvengr]

Are you sure that it is a Pro-197? I removed the covers from mine to see if I could read a part number and there is no diode or any other component between the power and external speaker jacks. The circuit board and jacks look nothing like mine. I am wondering if someone swapped the label on the rear of the scanner.

 

[tvengr]

shoot i put the wrong model up. It's actually a Uniden BC796D

Now I understand why I said Pro-197. Later today, I will check a BC796D to see if I can get a part number.

 

[pro92b]

I have not seen a schematic for the BC796D but there is one for the BC780, a somewhat similar radio. The schematic portion is attached. The kind of damage in your picture suggests that reverse polarity was applied to the radio's power jack. Replacing the diode should be easy - buy a replacement of the same package type with a 1 Amp rating. The voltage is not critical.

 

[MadMapper]

I have not seen a schematic for the BC796D but there is one for the BC780, a somewhat similar radio. The schematic portion is attached. The kind of damage in your picture suggests that reverse polarity was applied to the radio's power jack. Replacing the diode should be easy - buy a replacement of the same package type with a 1 Amp rating. The voltage is not critical.

tyvm, is the small white object in the corner where the trace turns, just a jumper? I am new to repairing my own electronics...actually this is my first adventure...lol

 

[MadMapper]

WOULD ONE OF THESE WORK?

https://www.mouser.com/c/semiconductors/discrete-semiconductors/diodes-rectifiers/rectifiers/?if%20-%20forward%20current=1%20A&maximum%20operating%20temperature=%2B%20150%20C&minimum%20operating%20temperature=-%2050%20C&mounting%20style=SMD%2FSMT&vr%20-%20reverse%20voltage=200%20V

 

[pro92b]

The diodes from Mouser will work. I don't understand your question about where the trace turns.

Looking at the circuit, the diode is shunted across the 12 volt power input in the reverse direction. With the correct polarity of 12V applied the diode does not conduct. It's as if the diode was not there at all. If the polarity is reversed, the diode looks like a short circuit. It is designed to blow a fuse in the power feed. If there is no fuse and the power source is capable of high current then the diode blows up. After that there is nothing to keep the reversed voltage off the radio circuitry and a large amount of damage is possible.

It there is continuity through T1 then the 12 volt input should make it to the on/off switch. If turning on the radio after checking for the presence of 12V does not bring up the radio, it may have suffered widespread damage. Before ordering diodes, do a few checks to determine if the radio can be salvaged.

 

[tvengr]

Do you have the original AD-580U transformer power supply with the ground pin? I don't see how you could possibly plug in into 2 outlets. Even if you managed to do it, an outlet strip has only a single phase and you could not get excess voltage. There is no way you could have the wrong polarity unless the AC power adapter has been modified or she used the wrong adapter. If she used the Uniden adapter, either the diodes in the adapter shorted and AC was applied to the scanner or the transformer shorted and applied power from the AC line to the scanner. I would be very leery about using the AC adapter. Ask her if she plugged in the wrong adapter. I pulled the cover off of my BC796D and saw that I would need to do some disassembly to get to the diode.

 

[KEWB-N1EXA]

It’s a protection diode
A. 1N 4001 would do just fine

Pete n1exa

 

[MadMapper]

TYVM, i made a jumper out of a bristle from one of my wire wheels, and she powered right up!!!

 

[MadMapper]

Do you have the original AD-580U transformer power supply with the ground pin? I don't see how you could possibly plug in into 2 outlets. Even if you managed to do it, an outlet strip has only a single phase and you could not get excess voltage. There is no way you could have the wrong polarity unless the AC power adapter has been modified or she used the wrong adapter. If she used the Uniden adapter, either the diodes in the adapter shorted and AC was applied to the scanner or the transformer shorted and applied power from the AC line to the scanner. I would be very leery about using the AC adapter. Ask her if she plugged in the wrong adapter. I pulled the cover off of my BC796D and saw that I would need to do some disassembly to get to the diode.

I have no clue how she managed to do it, but it is what she claimed happened. I got both scanners with no accessories at all. So she probably used the wrong power supply. She said they were her late brothers, and had no idea where the antennas, power supplies, or manuals were.

 

[tvengr]

i made a jumper out of a bristle from one of my wire wheels, and she powered right up!!!

That is probably steel which doesn't solder well. Use copper wire. What is the model of the other scanner? Is that a Pro-197? The Radio Shack scanners use a different plug. Here is the BC796D owner's manual:

 

[MadMapper]

yes pro-197, that one came to me working

 

[tvengr]

Does the 197 have a power adapter?

 

[MadMapper]

Not an OEM, I hard wired it temporarily. A car pulled out in front of my Harley 15 months ago, and I got tore up pretty bad. I still have about 8 more months of healing and physical therapy left to go. So I have become very creative on a non existent budget. :0 I don't even have the cables to program either of them, and scanners have changed alot since I was last an active listener.