Power supply blowing fuses in Zebra 2746e thermal printer.

[Toasty]

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

@Gianni - hmmmm. There is no connection between Hot side and isolated except thru the large trafo. No optos to couple signal etc. I think that the Hot side runs continuously supplying power to that winding to power up the 494.

[Toasty]

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

@Torin - Below point 1, do you have any voltages across the 2 large caps you replaced?

[torin3]

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

I thought you had 7 volts on IC1...?

Try it on AC scale or reverse the leads on DC.

Ok, tried again. I also reverifed that C26 is getting 6.6V and change across it.

I'm getting about 1 mV on 1-6 on DC. Changing the leads only changes the sign on the display from blank to -. On AC, I get nothing when both leads are connected. When only one is connected, I get about .4V.

Edit: Checking on the big caps now.

Edit-edit: 169 V DC across both caps.

Edit-3: Btw, I'm not getting discouraged. I'm finding this fascinating, and I'm really appreciative of the help you guys are giving me. Thank you!

[Toasty]

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

Correction (DOH!) - "There is no connection between Hot side and isolated except thru the large trafo."
T2 is also feeding the IC circuit. I think the voltage you're seeing at C26 is from T2.

[Toasty]

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

SCR1 should be open across the outside legs.

Please unplug and discharge caps. Then verify that D2, D3, D4, D5 are good.

I am concerned that since those 2 FETs nearby were blown in the beginning, and you're not getting any reading at Point 1 that something else is wrong on the Hot side.

@Gianni - I'm wondering if I'm looking at T2 incorrectly...? Could T2 be what is driving the FETs that were replaced? That would mean its primary is on the IC side and the secondary is on the FET side...?

Toast

[torin3]

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

SCR1 should be open across the outside legs.

Please unplug and discharge caps. Then verify that D2, D3, D4, D5 are good.

I am concerned that since those 2 FETs nearby were blown in the beginning, and you're not getting any reading at Point 1 that something else is wrong on the Hot side.

@Gianni - I'm wondering if I'm looking at T2 incorrectly...? Could T2 be what is driving the FETs that were replaced? That would mean its primary is on the IC side and the secondary is on the FET side...?

Toast

SCR1 was open in one direction, and 680 ohms in the other direction on the outside legs. All other combinations were open.

Can D2 - D5 be checked in the circuit, or do they need to be removed?

[torin3]

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

Can D2 - D5 be checked in the circuit, or do they need to be removed?

Took them out just to be sure. They are all good.

[torin3]

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

I need to clean the snake cages...I'll be offline for about 20 minutes.

[Toasty]

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

No need to quote.

Yes, check them in circuit. I'm looking for a short.

Attached pic w/ outlines T1, T2, SCR1, IC1

--
Edit: Okay on diode check and cleaning your snake.

[Toasty]

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

Where is the power on/off switch for this supply? On the mains side or the Printer?

[torin3]

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

Well, I guess I need an update then. D2 and D3 tested continuity both ways when in the circuit. D4 and D5 tested fine both in and out of the circuit.

On/off switch is mains side. External to the board and between the external plug and the internal connector B1.

Edit: BTW, SCR1 was tested out of the circuit.

[Toasty]

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

Ok. Wanted to make sure we didn't need to have printer connected to get it working.

A bit more research reveals that the output of IC1 drives Q3 & Q4 to drive T2.

EDIT: Dang! Well, you have checked most everything else. Try D1 & D13 near T1. What are they?

[torin3]

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

In the circuit they are testing continuity at less than 30 ohms all ways. Pulling them now to test them out of the circuit.

[torin3]

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

Part number is BYV32E-200.
Datasheet:

Out of circuit, first number pos, second number neg. Numbers are legs from left to right looking at the part number:
1 - 2 ~250 ohms
1 - 3 infinity
2 - 1 infinity
2 - 3 infinity
3 - 1 infinity
3 - 2 ~250 ohms

[torin3]

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

Progress! I think the crappy solder job I did prior to getting the Hakko shorted 2 pins on D1 or D13. When I put them back in, there was no continuity between the legs in the circuit anymore.

Now C26 is 15V DC

Poinst 5 and 6 that you asked me to test are now 25V DC each. Points 1 through 4 are still 0.

Edit: As a fellow east coaster, I know it is running late. I'll be up for about another 1/2 hour. I'll take the parts back into work, so I can do more tomorrow morning if needs be.

[Toasty]

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

Good News! Go back over all your solder work. Green light?

[torin3]

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

I checked. No green light. I think Q1 and Q2 are the only things I soldered with the old iron that haven't been gone over with the new iron yet. Checking now.

[torin3]

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

Touched up everything I might have hit before and still no change. LED doesn't light up, fan doesn't come on.

I'll try it in the printer tomorrow in case it needs some sort of load to fire up.

[torin3]

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

IT WORKS!!!

More details after I get it set back out on the shop floor and verify it doesn't have other problems.

[torin3]

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

Ok, brought it back to work. Plugged the PSU back into the printer, so I could test it with a load. Plugged it into the power strip and turned on the switch.

I heard a LOUD pop under my desk.

Some quick checking and I find out that I've popped the breaker and killed the power strip!

Our maintenance guy at work had left us last week, so I have to track down someone who knows where the breaker for my area is.

Turns out I have a 10 amp breaker for my desk and the next desk over! Yikes! I can have as many as 4 computers running at one time at my desk! And when I've got my folding rig running with 2 GX2 cards in it, it pulls about 850 watts by itself!

So, I'm scheduled now to get a 20 amp dedicated outlet for the computers at my desk.

But the printer still isnt' working. So I take it to a different 20 amp outlet, and try it again. It still trips the breaker!

Ok, time to do some thinking, so I take it back to my desk and stare at it for a bit. It finally hits me that I've got the power plug to the board in backwards. Hot to ground. (It doesn't help that the way the connector is wired, it looks like it is supposed to go in backwards...I've been careful to make sure the green wire was lined up with the ground symbol...but I spaced it this morning.) So I plug it in correctly and try it. It turns on!

So, I put everything back in and try it at the computer I pulled it from. Everything works as expected!

So, parts that died originally:
Bridge rectifier
Primary caps
2 transistors

Problems I caused:
Bad soldering
reversed plug

Thanks for the help guys! I now have a much better idea of what I need to do in troubleshooting before asking for help.

Also, I must say, running a good soldering station helps a lot in the process!