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I work at a small college that has a Contel Executone 3672 phone system installed. It's been there since the early 90's. This morning, all the phones in the building started ringing at the same time. When you pick up the handset all you hear is a lot of "high-voltage" static. I have reset the system several times, cleaned the various components, etc. but nothing has worked. Everytime I turn the system back on, all the phones start ringing continuously. My question is this: What's the best way to troubleshoot my problem? Should I be looking at replacing the ring generator unit or the DC/DC Converter or something else? Any help on this would be greatly appreciated.

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My guess would be the DC/DC Converter. It's been so long...someone else will jump in and I will grab my book when I get home tonight and check back.

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The DC/DC converter has test points on the front face. Check them with a good digital voltmeter. The +5 volts DC is perhaps the most likely culprit since it affects the processor and IC's directly. I seem to recall that there is a screw-type adjustment that can be made but please be very careful in turning it, as in fractions of a tick while you watch the meter. If anything, try adjusting it downward first to get a feel for the sensitivity of the adjustment process.

If that doesn't have any positive effect, chances are that you will need a new DC/DC card. That's about the only thing that fails in those systems and it's usually due to excessive heat. You may also want to try leaving the cover off and even pointing a fan toward it to see if there's any change in behavior. Fortunately, I don't think you will have too much trouble locating a replacement since that was quite a popular system.


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I metered the front test points and I'm getting 3.8 v on both the +5 and +14 ports. When I try to change the +5 adjustment screw, there is no change whatsoever in the voltage reading at either test point. I'm assuming from this that the DC/DC board is shot. I guess I'll check ebay.

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Please don't check e-bay for something like this. PM sent.


Ed Vaughn, MBSWWYPBX
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I have a new DC/DC converter installed and still have a problem. When I turn the system on and meter the test points, I'm getting 14v on the +14v test point, but only 2.2-3.6v on the +5v test point. Is this correct? Turning the adjustment screw causes all the relays in the system to click like crazy and then the +5v led gets real dim. Maybe something else could be the problem? Any help would be greatly appreciated.

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I would say that is out of tolerance, in skimming through the manual I didn't find the tolerances. It looks like you got the plus 14, I think I'd put a meter on it and start pulling packs to see what's dragging it down. Do all your testing from the blocks so as to eliminate any possible cable problems. Your voltage should be close to 5.


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Found the tolerances in section 801, your only allowed 1%, which would be about .5volts. I'd check them all while your at it to see if everything in within specs.


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I just detached the ring generator unit and now the system meters perfectly. I'm thinking a power surge may have damaged the RGU. Sound possible?

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Anything is possible, that's why I suggested what I did. See if other features are working without the ring generator.


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