PRO197 mostly dead (need Miracle Max!)

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krs

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I have 3 PRO197s that have worked fine but last night one of them that's only about 3 months old mostly died. The only thing alive is the lighted front panel, no text on the display, no audio, no nothing else.

Opened it up to look for anything obvious like burned resistor, etc but didn't see anything. Doing some checking I find the output of the LM317 is only about 1.4 volts...I am guessing since I have no schematic this is supposed to be the 5V supply and that something downstream is kaput. The 7808 fixed regulator next to it is working properly, that might be what powers the display and button backlights? I kinda doubt there's any circuitry in this scanner that uses 1.4 volts.


I suspected C195, the first component on the 317s output line so I took it out and it's fine. There aren't any shorted diodes or resistors in this area of the power section...the (presumed) 5V line runs off in several directions and disappears inside some shielded compartments, but I'm not about to start dismantling those things. I guess I'll scare up a new LM317, that's one gadget I don't seem to have, but I don't have a lot of faith that is the problem, it isn't dead shorted to ground and those things are usually pretty bulletproof.

Just thought I'd ask in case anybody has run into a similar problem and might have any ideas...thanks
 

iMONITOR

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You already sound like you know more than most would. However, have you tried the factory reset?
 

SOFA_KING

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I have 3 PRO197s that have worked fine but last night one of them that's only about 3 months old mostly died. The only thing alive is the lighted front panel, no text on the display, no audio, no nothing else.

Opened it up to look for anything obvious like burned resistor, etc but didn't see anything. Doing some checking I find the output of the LM317 is only about 1.4 volts...I am guessing since I have no schematic this is supposed to be the 5V supply and that something downstream is kaput. The 7808 fixed regulator next to it is working properly, that might be what powers the display and button backlights? I kinda doubt there's any circuitry in this scanner that uses 1.4 volts.


I suspected C195, the first component on the 317s output line so I took it out and it's fine. There aren't any shorted diodes or resistors in this area of the power section...the (presumed) 5V line runs off in several directions and disappears inside some shielded compartments, but I'm not about to start dismantling those things. I guess I'll scare up a new LM317, that's one gadget I don't seem to have, but I don't have a lot of faith that is the problem, it isn't dead shorted to ground and those things are usually pretty bulletproof.

Just thought I'd ask in case anybody has run into a similar problem and might have any ideas...thanks
Sounds like a good start. Did you lift the regulator output lead and check the voltage with no load? I would bet that it IS the problem, but that is what I would do next.
 

krs

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I can't do the software reset since no text ever comes up when I turn it on. I looked all around inside for any small momentary push button switches like are usually put in devices for that purpose - a hard reboot but couldn't find any..unless it's hidden way inside one of those cans I don't think it has one.

Edit to add, I still think that low voltage on the regulator output is way wrong, so a reset wouldn't make any difference in that case, I'm pretty sure.
 
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krs

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Wagoner, OK
Sounds like a good start. Did you lift the regulator output lead and check the voltage with no load? I would bet that it IS the problem, but that is what I would do next.
No, I didn't do that yet, I was thinking that the 317 has to have an external feedback loop to enable/regulate the output but now that you suggest it, I don't think it will hurt anything to try. It's over at my shop, will look at it this afternoon, thanks for the idea.
 

krs

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A little more info, no good news. I finally got some time to work on it, I ordered some spare voltage regulators (LM317) because I thought just simply replacing the old one was the easiest way to track down the problem. I was surprised to find that when I took out the old one, the front panel lights went out!...so apparently they are operated by whatever voltage comes out of this device, and predictably after observing that, putting in a new one brought me right back to where I was at first...nothing is alive except the backlights. i've had zero luck coming up with a schematic, so I will just sell the thing as non-working, for parts, on ebay, I have no interest in (or really any way to) dig into the inner bowels of the thing. Not sure if this information is helpful to anybody but I wanted to let you all know the final result.
 

krs

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Thanks James, I didn't know there were places that did repair on radio shack scanners...I guess I figured only RS would probably just swap out a broken radio for obscene amounts of $$$! :D
I appreciate the info!

.
 
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