PDA

View Full Version : Power supply blowing fuses in Zebra 2746e thermal printer.

torin3
09-03-09, 09:55 AM
In troubleshooting why the printer wasn't working, I noticed that it wouldn't even turn on. Pulling the power supply, I see the fuse is blow. Replacing the fuse results in the new fuse blowing instantly. A co-worker who has some experience with power supplies suggested checking the bridge rectifier. 2 of diodes were blown open. So I ordered in a replacement 6A 600V bridge. After replacing it, and turning on the power switch, it blows the fuse again. Pulling out the bridge and testing it, it is still good.

The PSU is a HiTek Power Corp. Model No. : TEK300SD-587

I've included pictures of the board below. Yes, this is after removing the bridge.

The large black caps are rated:
470μF 200V. I'm not sure how to read everything else on them. Below the ratings, one has 5522F and the other has 5530F. Picture 3 shows all writing on one of them.

Any suggestions of where to go?

http://i166.photobucket.com/albums/u90/torin3/oc/repair/psu1.jpg

http://i166.photobucket.com/albums/u90/torin3/oc/repair/psu2.jpg

http://i166.photobucket.com/albums/u90/torin3/oc/repair/psu3.jpg

http://i166.photobucket.com/albums/u90/torin3/oc/repair/psu4.jpg

http://i166.photobucket.com/albums/u90/torin3/oc/repair/psu5.jpg
WonderingSoul
09-03-09, 10:20 AM
I assume no caps are bulged or potentially leaking?
Oklahoma Wolf
09-03-09, 10:26 AM
I'd start by checking those transistors in the gray hoods for shorts between pins, particularly the two big ones on the primary side.
torin3
09-03-09, 10:41 AM
I assume no caps are bulged or potentially leaking?

Not that I could see.

I'd start by checking those transistors in the gray hoods for shorts between pins, particularly the two big ones on the primary side.

Well, given I'm fairly inexperienced here, I'm assuming I don't have to take them out of the board to test them.

The two big ones are short (resistance reads about 0) on any combination of the 3 leads. Of the 3 small ones. 2 of them are the same way, the third is short across the two outside leads, but outside to center lead is not short.
Oklahoma Wolf
09-03-09, 10:52 AM
You should remove them to test them - other nearby components in the circuit will interfere with the reading. Just use the diode checker on a DMM - if one or both has shorted pins, it will be obvious, reading something like 0.03 ohms in each direction.

If those parts are really all blown, I'd be concerned that the printer is overdrawing the PSU. You may not be able to find replacement parts for all those.
torin3
09-03-09, 11:00 AM
You should remove them to test them - other nearby components in the circuit will interfere with the reading. Just use the diode checker on a DMM - if one or both has shorted pins, it will be obvious, reading something like 0.03 ohms in each direction.

If those parts are really all blown, I'd be concerned that the printer is overdrawing the PSU. You may not be able to find replacement parts for all those.

I only have an analog MM right now. They do have a DMM here I might be able to borrow, but I'm not sure of the features.

I'm not sure about overdrawing, we have at least one other printer of this model here, but I can guarantee we have crappy power. Figure about 100 machines with 30 HP or larger motors stopping an starting all the time.

Starting to unsolder them from the board.
Oklahoma Wolf
09-03-09, 11:06 AM
Just measure resistance then - that's all the diode check does anyway :)
torin3
09-03-09, 11:30 AM
Just measure resistance then - that's all the diode check does anyway :)

First one out reads near 0 resistance in any combination.

Edit: Same for the second one.

Edit2: First of the small ones I think is good. Several combinations are near infinite resistance, and other while low are around 1.5KOhm The big ones have a part number on both of them 2SC2625. Below that is 5334 in smaller numbers.

Edit3: Found a place to order them online. I should have them Monday or Tuesday. Too bad I won't be in until the next week due to the plant being idled.
torin3
09-17-09, 09:21 AM
Ok, finally got it working today. After some misadventures with tripped breakers and the like.

Parts that went bad were the bridge rectifier, the 2 primary caps, and the 2 big transistors.

I didn't help it when I resoldered the 2 smaller hooded ones after checking them. Looks like I managed to bridge two legs. It was much easier to solder them properly with the Hakko 936 than the RS 30w soldering 'gun'.

Running fine now. :beer:
Oklahoma Wolf
09-17-09, 09:30 AM
Good to hear you got it working :)