Pro-96: Does Not Power Up

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JOEG7311

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Jun 22, 2011
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Mount Prospect IL
My Pro-96 will not power up with battery clip or external dc power. The only sign of overheating is to D31. I cannot read the marking on this component. I believe it is a diode of some type, not sure as to the type, rating or polarity. Any case marking identifier would also be helpful. Would failure of this component result in no power up by either battery clip or external dc power? Thanks for you help in advance.

Joe
 

n5ims

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Since I don't have a Pro-96 or the service manual, I can't guarantee my answer but chances are good this is the "reverse polarity protection diode" that's designed to blow quickly when power to the scanner is supplied with the polarity wrong (positive where the negative should be and vice-versa).

This can happen quite easily when using one of those common "adapt-a-plug" supplies. These plugs are "wall warts" sold by companies, like Radio Shack, where you get the wall wart that provides the correct voltage and current and then purchase the correct plug for the device you plan to use it with. The various plugs all have a common connection on the side the connects to the wall wart and different outside and inside diameter connections to mate the device it's being used on. Since the polarity is selected by plugging the plug into the wall wart's cord one direction for a center positive and the reverse direction for a center negative connection. It's easy to get this wrong and damage your device.

Several manufacturers have designed their equipment with a reverse polarity diode across the power connection so when plugged in correctly it doesn't conduct, but when the polarity is supplied in reverse, it conducts and quickly destroys itself, preventing the incorrect power from damaging the device beyond the easily replaced diode. This is why I guess that diode appears to be damaged and the scanner no longer working. It should be a fairly quick and cheap repair to replace it and get things working again. Unfortunately, that probably would require a service manual or schematic.

My beef over this type of protection is the protection is basically a suicide protection and requires a service call to repair the damage. Sure the diode is cheap, but you'll pay more for shipping and service fees than the diode costs. Now, if they'd spend a bit more ($0.25 instead of $0.10) and used a full wave bridge rectifier chip instead, it wouldn't make a difference what polarity the supply was, it would simply work and a reverse polarity problem would cause no damage, nor even be noticed.
 

pro92b

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D31 is a Rohm type RB060L-040 Schottky diode rated at 2 Amps and 40 volts. It is in series with the battery and if you remove the battery and power from only the AC adapter then D31 is out of the circuit. You probably have other parts blown, like L29 open circuited. Check the attached schematic and measure the DC voltages in your radio to see where it is going wrong.
 

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JOEG7311

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Jun 22, 2011
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Location
Mount Prospect IL
Thank you pro92b and n5ims for the replies to my message. The information and schematic were very helpful. After much review I found an open circuit trace. After making the repair, the radio is working well. I realize that it is old, though it still works. Need to figure out programming next.
 
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