Brother MFC-7820N printer/fax/copier- no longer powers up, except LCD backlight

[johne]

Hello,

I posted this in another forum, but this one seems more applicable in retrospect. have a Brother MFC-7820N multi-function printer/fax/copier that has stopped working. The LCD backlight comes on, but nothing else (display is totally blank). It does not sound like it is warming up at all. This machine stayed powered on all the time, and as far as I know, there was no material incident that triggered this. Just one day it would no longer print or respond to any keypad entries.

I removed the power supply board and examined it, and found a burned looking area around component D120 (per the attached pictures), which appears to be a diode (next to capacitor C101). I'm guessing that diode is my problem, unless others have better ideas? Does anyone have a schematic or parts list for this board, or are you able to identify this component for me?

I did a little looking around online, and it seems that PCPS0826 power supply board is the same as P/N: MPW5811, which should work for the mfc-7820N printer, mfc-420, and dcp-7020. So if anyone has info for any of these models, I guess it should be applicable as well?

Thanks for any help!

 

[Gryd3]

Hello,

I posted this in another forum, but this one seems more applicable in retrospect. have a Brother MFC-7820N multi-function printer/fax/copier that has stopped working. The LCD backlight comes on, but nothing else (display is totally blank). It does not sound like it is warming up at all. This machine stayed powered on all the time, and as far as I know, there was no material incident that triggered this. Just one day it would no longer print or respond to any keypad entries.

I removed the power supply board and examined it, and found a burned looking area around component D120 (per the attached pictures), which appears to be a diode (next to capacitor C101). I'm guessing that diode is my problem, unless others have better ideas? Does anyone have a schematic or parts list for this board, or are you able to identify this component for me?

I did a little looking around online, and it seems that PCPS0826 power supply board is the same as P/N: MPW5811, which should work for the mfc-7820N printer, mfc-420, and dcp-7020. So if anyone has info for any of these models, I guess it should be applicable as well?

Thanks for any help!

It would help keep things cleaner if you asked to move the original instead of making a duplicate.
Do you have any test equipment, how are you with electronics?
It looks pretty dark... but the components don't 'look' damaged to me.
Have you been able to verify the power supply board is the culprit?

 

[KrisBlueNZ]

I've deleted the other thread. This is the right forum.

I agree with Gryd3 that there is no obvious damage, just a bit of darkening due to constant heating. Although there could still be a fault there.

I think your first step is to measure the voltages on the output connector at top right. Do this initially with everything plugged in. If it turns out that a voltage rail is missing or wrong, you will have to measure it again with the connector unplugged, but we need to know where to start looking initially.

There are only two supply rails: +5V and +24V. The 0V rail is on pins 1, 6 and 7 of the connector, and this is where you should connect your multimeter black probe.

Set the multimeter to DCV (the 200V range, if it's a manual ranging meter) and measure the +24V output on pins 4 and 5. I suspect it's probably OK but you might as well check it.

Set the multimeter to DCV (the 20V range, if it's a manual ranging meter) and measure the 5V rail on pin 2 of the connector.

If there's a problem there, can you post a picture of the underside? According to the schematic, fuse F103 is in series with the 5V output, but in your photo, the F103 position doesn't have a component! So unless the fuse has fallen out of the board (not likely), or you removed it (and didn't tell us), there must be some other way for the 5V rail to get topin 2 of the connector.

The other pins of the connector control other part of the unit - one enables the mains supply onto the heater; one enables the DC fan; two seem to control LEDs, and one seems to come from a front panel sensor.

 

[johne]

Hi, sorry about that, wasn't quite sure how to request that. Maybe the other thread can be deleted?

I'm pretty decent with electronics. I don't have access to an o-scope, but I do have a multi-meter. As for verifying the power supply board, I'm not sure how to be certain of that without any schematics or expected values. However, there is one main pair of wires exiting the power supply, along with some smaller wires that I'm guessing are more TTL level. The main pair of wires exiting the power supply has a connector. I unplugged that connector, and checked the voltage between the wires. It read 110V AC. Next, I plugged the connector back together, and re-checked the voltage across the same 2 wires on the back of the connector. It now read 11-12 V AC.

I'm not quite sure how to interpret that, except that obviously under load the power supply is being pulled down. I don't know if that's due to a fault with the power supply itself, or some other component pulling it down, but I was guessing the power supply.

 

[johne]

Hi Kris, it looks like our posts must have crossed, and you finished yours before I completed mine. Anyhow, thanks for cleaning things up, and for the further information. I will check the connector you mentioned and let you know what I can find there. I will need to take apart the power supply module to do that, so it will probably be tomorrow before I can get to that.

Here's a picture from the backside of the board. The upper left corner in this pic corresponds to the upper right corner in the front side pictures.

edit #2- was actually able to measure the voltages easily enough on the backside of the board, once I understood where the connector was. pins 1-2=5V, pins 1-4 or 5=24-25V

 

[johne]

Does anyone have any further ideas or suggestions on how to proceed?

 

[KrisBlueNZ]

I was waiting for those voltage measurements and I didn't notice you'd edited post #5.

Well, it looks like the power supply is OK. So you need to follow the 5V rail on pin 2 of the connector and see why the rest of the unit isn't doing anything.

I found two versions of the service manual:

http://elektrotanya.com/brother_dcp7020_mfc7420_mfc7820n_en.pdf/download.html
http://fehu.whitequark.org/files/brother_mfc-7420_7820_dcp7010_7020_7025_sm.pdf

but both of them have schematics for only the "NCU" board and the power supply. No schematic for the main board. Lots of instructions and fault-finding guides for mechanical problems and that kind of thing, but nothing that would help with this problem. Just an overall connection diagram showing how the boards connect to each other.

Can you follow the +5V rail to the main board. It looks like it comes in on CN21, pin 11. Can you take some photos of both sides of the board in that area, and check any fuses you can find.

 

[johne]

Hi Kris, thanks for that. I'll look into that next. Any thoughts regarding the voltage drop in post #4 (from 110V to 11-12V AC) on the main pair of wires exiting the power supply when the connector is plugged together?

I'll try to follow the 5V back and see what I can find.

 

[lemonherb]

This just happened to me as well. I had unplugged it to temporarily move it to clean around the area and when I plugged it back in, nothing worked but the LCD backlight

I proceeded to open up the power supply to search for anything obviously damaged. Nothing there, but similar scorching around that same diode as yours.

I checked the other two circuit boards, but nothing stuck out, capacitors were all intact and everything looked pretty much pristine.

I had resigned myself to having to go buy a new printer tomorrow and thought, what do I have to lose by smacking it on the sides.

No results, then I picked up the printer a couple of inches and slammed it down while power switch was on, then all of the sudden the warm up sequence ran, and the LCD activated and all the buttons worked.

I ran a copy, scanned a document and printed just fine.

Crazy!

Hello,

I posted this in another forum, but this one seems more applicable in retrospect. have a Brother MFC-7820N multi-function printer/fax/copier that has stopped working. The LCD backlight comes on, but nothing else (display is totally blank). It does not sound like it is warming up at all. This machine stayed powered on all the time, and as far as I know, there was no material incident that triggered this. Just one day it would no longer print or respond to any keypad entries.

I removed the power supply board and examined it, and found a burned looking area around component D120 (per the attached pictures), which appears to be a diode (next to capacitor C101). I'm guessing that diode is my problem, unless others have better ideas? Does anyone have a schematic or parts list for this board, or are you able to identify this component for me?

I did a little looking around online, and it seems that PCPS0826 power supply board is the same as P/N: MPW5811, which should work for the mfc-7820N printer, mfc-420, and dcp-7020. So if anyone has info for any of these models, I guess it should be applicable as well?

Thanks for any help!

 

[Harald Kapp]

Posting to a 4 year old thread is not meaningful. Thread closed.