atcomsystems.ca/forum Forums TDM Business Telephone Systems NEC Telephones & Systems NEC Electra Pro Power Supply Question

Hi, I'm a long time electronic tech with an audio equipment repair company. We have an NEC Electra Pro system that went down recently. For now we're limping along on cells and a couple of single line phones that are tied to the CO lines.

I think my question is fairly simple, but first some quick background on the problem. We've had our system for many years and it's been quite reliable until last week when it died completely. I saw that the PSU (PSF-H-20) was dead and pulled it out. The main fuse was blown and it showed signs of running warm for a long time but there were no burned areas. I bought a new supply and tested it today. Before the first power up I installed the PSU with 3 DVM's across the OV, -27.3, +5, and -5 sections of the edge connector. (DVM 1 between 0 and -27.3, DVM 2 between 0 and -5, and DVM 3 between 0 and +5.) I checked for shorts, saw none, and powered up the card. -27.3 came up as expected but I was surprised to see that although I got 10 volts between the -5 and +5 pins, I didn't see 5 volts between ground and either of those pins. (I was using little grabber clips, hung off the 90 degree leads of the male edge connector, inside the board.)

I went ahead and powered up, at first with the CPU board only. The voltages were unchanged and after a few seconds the green status LED began blinking. I powered down and reinstalled the other cards one by one, checking each time to be sure that the voltages didn't change. They didn't, but none of the phones came online. No display, no LED's, nothing.

So now I come back to my question: is it normal not to see 5 volts between ground and the -5 pin, or between ground and the +5 pin? That makes it look like one 10 volt rail, not two 5 volt rails. It just seems odd to me, and i was very careful measuring it. Am I missing something here? I was just wondering if maybe there's some link or fuse or something inside the cage, that might have opened.

If it is normal, I guess the next step is replacing the CPU board, even though the status LED looks normal.

Thanks in advance for any help with this.

How long did you wait?

If the PSU was bad you would not see the run light flickering on the CPU. I usually measure those voltages off of the back of the connector to the backplane of the KSU. Insert your plrobes into the back of the connector. You should see the proper voltages. Usually those power supplies go bad before the fuse blows. You may have a problem with the KSU itself. Was there any water damage or burning on the backplane. You may need to inspect it from behind, which means removing the KSU from the wall and removing the rear cover.
Is this an EPRO I (plastic cabinet) or EPRO II (metal cabinet)?

Thanks for the replies. Coral Tech, I had waited about 5 minutes.

Today I got a new CPU board, and now the system works again, with the default settings. So my PSU and CPU were both definitely bad.

The good news is, my system is back up. The bad news is, now I need to completely reprogram it, yikes! I originally set it up about 10 years ago and being an audio tech and not a PBX guy it took me a long long time, even with all the right manuals. I recall that 90% of it was fairly straight ahead, but the last 10% was very slow and I could only finish it with the help of an outside tech or two.

Is there anybody around who might be able to fix my old CPU? Or is there any way I might be able to move its backup RAM to the new CPU board? I realize I'd have to do that with battery power maintained to the IC's the whole time, which would be tricky but not impossible. (The battery in the old CPU is still good.) Our shop has done stuff bench stuff like that with audio gear. Both of these things seem a long shot, but I have to ask.

Barring all that, are any of you guys NEC techs in the Los Angeles area, or can you recommend anyone to help me get things back to normal. The tricky things for me will be the ring selections, the SLT stuff, one extension that behaves like an intercom, and a few oddball things that our setup requires.

Thanks again.

The only way to get the database out is to power up the card, install a MIF card (used to connect to the CPU) and the SAT program (https://www.nectekhelp.com/keysystems.html). The CPU may power up if you default it. Turn off the battery then power up at default. This will delete your database. I suggest trying that to see if it recovers to be used as a spare card. However your database is most likely lost.