MTR-2000, Need help with broken power supply

[sm2oan]

Hi We have a MTR-2000 as our local VHF repeater. IT has worked for 10 years with out any problem. Now the 250W Power supply is broken. It produce 9V and 4V instead of 14V and 5V. Is there anyone who have information about how to repair it or have schematics, we just have the installation manual which is quite useless in this case.

Rgds Mike/sm2oan

[kcbooboo]

Those supplies were made by other companies and Motorola didn't release schematics for them. Essentially it's a "field replaceable unit" meaning you don't take it apart or try to fix it, you just unplug it and replace it.

The 14V is regulated down to 5V, and as their both low, chances are good that if you can get the 14V back, the 5V will also recover.

If the station has DC input connectors, the simplest thing to do would be to power the station from an external 14VDC power supply and reconfigure it through software so it knows DC is the primary power source. If not, a new 250w supply is probably your only option. Motorola will repair/replace one for just about the same price as they can sell you a new one.

Bob M.

[sm2oan]

I have tried to power the radio with 14V via the DC-connector and it works then. The 5V output is ok also when DC-powered. But I guess the other problem is quite simple to fix if you got schematics. Probably we will end up with a external 14V PS an new PS is quite expensive I guess.

Rgds Mike

[Tom in D.C.]

If you can find a good electronics technician locally he/she should be able to troubleshoot and fix your power supply with little or no difficulty and probably save you a pile of money at the same time.

[kcbooboo]

I had a similar problem on a 100w UHF station. That supply starts with 28VDC, and that was not working right. So I took the cover off. All of the power transistors are mounted to the heat sink, and the circuit board is on top of them. I could loosen all the screws on those devices but the board still would not budge. I have a feeling that they use some kind of adhesive-type heat sink compound that prevents the supply from coming apart unless I used physical force. I was considering unsoldering all of their leads from the circuit board, but they weren't all accessible without unsoldering other parts. Essentially they made the supply NOT to be repaired. The only thing they could have done to make it worse would have been to encase everything in epoxy.

Also, this is a universal switching supply that runs right off the raw AC input voltage, so working on it could be considered hazardous. It probably could cause cancer in California (I think everything is a known carcinogen in that state).

Using an external supply is simple and far less expensive than replacing or even trying to repair the stock supply.

Bob M.

[VolFireJunkie]

I have recently picked up a 100W UHF. Its condition was unknown when I got it. With some investigation the internal components of the PS are in horrible condition. I am unable to figure out if it took an AC surge or lightning strike.

With that said, I would entertain investing some money if I was sure that the PS was the only bad part. I tried to put 14v to the DC in connector but nothing. I do not have immediate access to a 28v ps or I would have tried that, but I was told that 14v would make it power up, it just wouldn't operate at full power.

Can anyone assist me with instructions on how to bypass the ps (using an external ps) to feed power to the repeater.

Many thanks in advance!

Adam K.

[d119]

I have recently picked up a 100W UHF. Its condition was unknown when I got it. With some investigation the internal components of the PS are in horrible condition. I am unable to figure out if it took an AC surge or lightning strike.

With that said, I would entertain investing some money if I was sure that the PS was the only bad part. I tried to put 14v to the DC in connector but nothing. I do not have immediate access to a 28v ps or I would have tried that, but I was told that 14v would make it power up, it just wouldn't operate at full power.

Can anyone assist me with instructions on how to bypass the ps (using an external ps) to feed power to the repeater.

Many thanks in advance!

Adam K.

How did you get it disassembled? Perhaps you can share that info with kcbooboo and he can get his apart to work on it!

[kcbooboo]

I tried a pair of 12V UPS batteries in series; when they worked, I ended up buying a Uniden (made by Astron) 28V 18A power supply for $100 on fleabay. Plugged that into the battery terminals and the station worked fine. Maybe I was just lucky that the 14V and 5V regulators in my original supply were still working.

The supply opens right up after you remove the fan and 8 Torx T20 screws (as does the PA). That wasn't the problem. There's one main circuit board and a bunch of screws hold it to the heat sink. All of the pass transistors, SCRs, and big diodes are attached to the heat sink. There are holes in the circuit board to access the mounting screws. After removing all of the screws, the board still would not budge. I didn't want to pry it up because that would have broken it. ALL the pass transistors have some kind of permanent heat sink compound (adhesive) holding them to the heat sink. I was going to try unsoldering all of them from the circuit board but I couldn't get to all of them due to other things being in the way. I'm pretty sure two of the main DC filter caps had leaked or shorted and some foils had been destroyed, but I needed access to the underside of the circuit board and I could not get to it. This whole assembly was made NOT TO BE REPAIRED and they did a good job of it.

No schematics are available but I did figure out a lot about it through a block diagram. Mine was made by ABB but I understand a few other companies also made the supplies for Motorola. Basically they start with 120 or 240VAC, rectify that to about 360VDC (using a bridge rectifier configuration if 240VAC or a voltage doubler if 120VAC), and that powers an oscillator which drives a transformer which comes out with around 20VAC. This is rectified to give them 28VDC for the 100W PA, and also two other regulators to derive 14VDC and 5VDC. I have a feeling that the problem with my supply is in the 120V/240V switching circuit, or the 360VDC supply/oscilator circuit as I can see leakage under the large filter caps.

Bob M.

[VolFireJunkie]

sorry for the delay in reply, but it seems that kcbooboo got as far as i did. you can open the ps and get to the top og the board, but once you dig down to the bottom board it is stuck in place.

after i posted this originally, i tried to locate a wiring diagram for the 2 connectors that come out of the ps. but unfortunately i can not locate them. i figure in theory, one of this must carry the 14vdc and the other the 5vdc. in my thinking this may power up the repeater. i have a friend that says he can come up with a ps to test the repeater, but catcing up with him has been a challenge.

i'm still open to thoughts and ideas.

thanks,

Adam K.

ackarsin (at) gmail (dot)com

oh, is it me or are the dates all messed up?

[kcbooboo]

The pins on the backplane power connector can be found in an MTR2000 Backplane Connector article on repeater-builder. The PS connector is similar but might be oriented differently. Just follow the wire colors. The AC Power OK signal goes to ground to indicate you have AC present, or pulled to +5V if not, although it only affects the way the station reports errors or chooses to run on lower power when on battery. You need 14V and 5V (approximately) at a bunch of amps.

The 100w PA runs on 28V and 14V, while the 40w PA runs on 14V. Power comes directly from the PS.

On the high power PS, the external batteries provide 28VDC and the regulators in the PS drop that down to 14V and 5V. I suspect that on the low power PS, the external batteries provide 14VDC and the regulator in the PS drops that down to 5V.

Bob M.