Power supply blowing fuses in Zebra 2746e thermal printer.

[torin3]

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?

[kc8adu]

Re: Power supply blowing fuses in Zebra 2746e thermal printer.

looking at the fuse i vote shorted choppers.the 2 transistors near the primary caps.

[torin3]

Re: Power supply blowing fuses in Zebra 2746e thermal printer.

looking at the fuse i vote shorted choppers.the 2 transistors near the primary caps.

Yep, both of them were shorted out. Thanks!

[torin3]

Re: Power supply blowing fuses in Zebra 2746e thermal printer.

Well, the two transistors should arrive today, but I noticed that under the plastic top to one of the primary caps (the one with the Q.C. / PASS sticker on it), the top of the cap feels domed. So I ordered this one: http://search.digikey.com/scripts/Dk...words=P6120-ND Which looks pretty close to what the markings are (85°C and the like).

However, I didn't realize Digikey would be shipping it from North Dakota, (and it looks like I'd mixed up Minnesota and Michigan) when I picked UPS ground as shipping. So, given I can probably get this one (105°C rated) http://search.digikey.com/scripts/Dk...name=P10108-ND faster if I order it sent USPS, should I? It has a slightly higher ESR resistance.

Also, given that the original cap isn't shorted, would it be ok to test it with it still in there? I mean just turning it on and seeing if it blows the fuse again, and then turning it back off.

[Krankshaft]

Re: Power supply blowing fuses in Zebra 2746e thermal printer.

Get the primary cap in 105 C I think it being that close to those unheatsunk FETs (and it being 85 C rated) could have baked it.

For proper sizing refer to the datasheets you're looking for radial snap ins I use Panasonic too.

Look into the TS-HA, TS-HB, TS-HC, or TS-ED series. They all are line voltage rated at 105 C.

The different series' come in an array of sizes one series will have one at the proper voltage and capacitance that fits. Measure the original cap especially diameter and height in mm and look at the sizes on datasheets.

Be sure to look up the sizing before you order again don't want it not to fit.

TS-HA:

TS-HB:

TS-HC:

TS-ED:

All stocked by Digikey.

ESR isn't an issue on line filters they're just GP caps.

[momaka]

Re: Power supply blowing fuses in Zebra 2746e thermal printer.

Change both input capacitors at once. If one looks bad, chances are the other one is going that way as well.

[torin3]

Re: Power supply blowing fuses in Zebra 2746e thermal printer.

Change both input capacitors at once. If one looks bad, chances are the other one is going that way as well.

Will do. Though I am curious, there is only one visible difference in their markings. Below the ratings, one has 5530F, and the other has 5522F. Could anybody tell me what the difference is?

I'm planning on replacing them with 2 of the Panasonic TS-HB caps:
http://search.digikey.com/scripts/Dk...name=P10108-ND

[Toasty]

Re: Power supply blowing fuses in Zebra 2746e thermal printer.

Nah. Thats a date/batch/sequence code from when it was made.

HB's are fine. Just verify can size and lead spacing.

Toast

[torin3]

Re: Power supply blowing fuses in Zebra 2746e thermal printer.

No problem there. They are both 22mm dia 35mm long and 10mm lead spacing.

[torin3]

Re: Power supply blowing fuses in Zebra 2746e thermal printer.

Well, I got them off the board, and the one that felt like it had bulged had indeed bulged. Also had evidence of leaking at the base too.

Took a bit of work to get the caps off though. Ratshack 30w 'gun' had a hard time with that much lead free.

Hakko station should have arrived today, but looking at the shipping status, I think I'm going to have to call them. Ordered it UPS ground from New Jersey to Eastern PA (about 70 miles) and 9/8/09 it was listed as pulled and expected to ship 9/8/09. Still says that now.

[torin3]

Re: Power supply blowing fuses in Zebra 2746e thermal printer.

Got the soldering station yesterday. Today the caps arrived. I put everything back together and fired it up.

Good: It isn't blowing the fuse up anymore.

Bad: It isn't turning on. I'll bring my camera and multimeter to work Monday and post pics and do any tests you guys have for me.

[torin3]

Re: Power supply blowing fuses in Zebra 2746e thermal printer.

Ok, here are the current photos. The smaller transistors I took off and checked don't have that great of a soldering job on them, so I'm probably going to desolder them and resolder them.

Again, a quick rundown of what I've done so far:
Report that the printer isn't working. Checked printer, found it wouldn't turn on. Checked PSU, found blown fuse. Replaced fuse and tried to turn on. Fuse blows again. Checked and found bridge rectifier bad. Replaced and tried to turn on. Fuse goes again. Pulled rectifier, found to be still good. Found 2 bad transistors. Noticed one of the large caps is swollen and leaking. Replaced caps and transistors with new parts. Tried to turn on. Won't turn on, but fuse no longer blows.

[Gianni]

Re: Power supply blowing fuses in Zebra 2746e thermal printer.

If the Power Transistor were shorted probably the IC controller IC1 is dead too.

I can't recognize it; check the part number, find the datasheet and check voltages on the pins. Check also the small transistor Q3-Q4 and the components around them, if I'm not wrong they are part of the Power Transistor driving circuit. Check if T2 has open winding because it drives the transistor, it is used to drive Power Transistor and to keep isolated the primary side from secondary side.

Check also the components around Power Transistor, I see some diodes/zener and resistors.

Ciao
Gianni

[torin3]

Re: Power supply blowing fuses in Zebra 2746e thermal printer.

It is a Texas Instruments TL494CN

Data sheet here:

[Gianni]

Re: Power supply blowing fuses in Zebra 2746e thermal printer.

I'm a little bit confused: the TL494 is on secondary side and to start it needs voltage on PIN12. Usually the start up voltage come from input through a high value power resistor (100~300K 2~3W), it charges the CAP on Vcc and when the IC/PSU works tha voltage come from auxiliary winding.
In this PSU I can't understand how the TL494 receives the start up voltage and if it were connected to the input there will not isolation between primary and secondary.
Anyway D23 D24 and C26 should be the rectifying circuit for the auxiliary winding, check if you have voltage on C26.

Ciao
Gianni

[torin3]

Re: Power supply blowing fuses in Zebra 2746e thermal printer.

C26 is getting about 7V

[torin3]

Re: Power supply blowing fuses in Zebra 2746e thermal printer.

Oh, and thank you for the help. Sorry if I'm a little confused at times. Most of my electronics knowledge is from high school and I've had more than 20 years to forget it.

[Krankshaft]

Re: Power supply blowing fuses in Zebra 2746e thermal printer.

If the bridge rectifier was blown and a surge took the rectifier out be sure to make sure that the startup resistor isn't blown open. The PWM can't start unless it gets that kick from the resistor. The only resistor that fits the bill is the one behind that line choke to the right of the line fuse.

If the resistor is fine I agree the PWM IC was probably taken out.

From New Jersey you say and it said pulled for shipping. You ordered from tequipment.net didn't you ?

I did too they gave me 40 bucks off my FX-951 they had none in stock and had to order it and it took a week though . For future reference UPS ground shipments to from NJ to PA and vice versa usually arrive next day.

If you really want to know when a package will arrive go here:

http://www.ups.com/maps?loc=en_US

And generate yourself a time in transit map Fedex has them too.

http://www.fedex.com/grd/maps/ShowMapEntry.do

If I need a part in a hurry this is how I calculate where to order from.

[torin3]

Re: Power supply blowing fuses in Zebra 2746e thermal printer.

Krankshaft, is that R1? And I'm not sure I'm reading the code right, as I can't tell if that first stripe is grey or white. If it is grey, I think it is supposed to be 820Ω. In any case, I'm getting a reading of about 50KΩ from my analog multimeter, and the digial I borrowed has a max limit of 4KΩ and it says over limit.

So, I should replace it? And is it 820Ω? And what wattage should it be?

[Gianni]

Re: Power supply blowing fuses in Zebra 2746e thermal printer.

C26 is getting about 7V

It's low but it is the min Vcc accepted by TL494.

I'm still curios to know where the voltage comes from.

R1 is to far from IC1 I think it is not the start up resistor, it's value is 820ohm probably 1W, the value is too low for start up.
If you read 50Kohm be sure all caps are discharge, you can lift on leg and measure it disconnected. If it is 50Kohm then replace it with 820ohm 1 or 2W.

Looking at the pictures I see IC3 near D13: have you identified it?
Maybe it is another part to check.

Ciao
Gianni