dead paper shredder with crap caps

[cyclones]

I am trying to troubleshoot a dead paper shredder. It is a rather beefy looking thing from Staples. Big motor. It will not power up. None of the LEDs on the panel come on. I checked the simple things like power cord and fuse and no problems there.

Looking at the main board, it is a super cheap design. It has no transformer, just resistors, a few electrolytic caps (zckj or something like that -- a known bad brand) and four diodes. Then there are a couple of relays to control the motor. The board also has an 8-bit Samsung microcontroller on it and a couple of polyester or ceramic capacitors. That's pretty much it. I was going to start by replacing the 5 electrolytic capacitors with high quality ones and see what happens since it's only a couple of $ to do that.

Any other ideas on what to check? Thanks!!

[retiredcaps]

Originally Posted by cyclones

Any other ideas on what to check? Thanks!!

Can you post a picture so we can suggest test points?

[cyclones]

Here is a photo of the board that I took. I did replace the crap caps with good ones but still the board appears dead. There is definitely continuity from the plug to the board.

[digge]

DZ902-DZ905 is probably diodes working as a rectifier, make sure those are ok. Would be easier to figure it out of you had a photo of the back of the board as well. I cant read the numbers on the small IC but guessing its a voltage regulator? If it is, find a datasheet and measure the output pin and see what you get.

Im also assuming the relays are for forward and backwards drive of the motor, they are not used for power on?

[Scenic]

Originally Posted by digge

I cant read the numbers on the small IC but guessing its a voltage regulator?

The small 8pin IC says "ATMEL 24C___" (unreadable), so it's most likely an EEPROM.

Opening the image in a new tab shows it in it's full size, rather than the stupid javascript resizing mess when you click on it, which will be larger, but still not the original size.

[multimeter]

i may be wrong but those lytics look like g-luxon caps?,if they are they are general purpose ones,panasonic fc series is a good near match replacement

[cyclones]

Yes, I thought the diodes were probably performing the rectifier function. I tried getting continuity across DZ902 and can't seem to get anything either direction. The caps in the photo are new Panasonic.

[mariushm]

It's a Zener diode, most likely.. a bit harder to test.

[Th3_uN1Qu3]

A zener is still going to behave like a normal diode in forward mode, so you should have been getting a reading in one direction. It could have failed open.

[budm]

It has current source power supply setup (Capacitive Transformerless Power Supply) using Xc of the capacitor to drop the voltage instead of using resistor which the resistor will get hot due to power dissipation) to put out 24Vdc to power the relays and there are resistors/Zener Diode to rugulated the voltage to run the IC's.
Need good pictures of the backside of the board.
If you trace out the connection on one leg of the fuse, it should go to low Ohm resistor, another end of the resistor will be connected to one leg of that large brown cap, the output of the brown cap should be connected to the rectifier circuits and Zener Diode to regulated the voltage.
To check Zener voltage, all you need is variable DC power supply and 1K resistor (to limit the current) in series with the Zener, and DMM.
Plus output of the power supply to resistor, output side of the resistor to the Cathode of the Zener, Negative to the Anode. Put the DC meter across the Diode, turn up the power supply output until it does not go up anymore even you keep putting out more voltage, what you see on the meter will be the Zener voltage of the Diode.
By the way, please also post new direct front view of the board so we can see all the parts.

[cyclones]

Here is a photo of the back side of the board. What spec of zener diodes will I need, assuming the diode(s) is/are the problem?

[budm]

Can you please do straight shot of the board both top and bottom sides instead of tilted pictures? Also use the attachment to post the pictures. It is hard to trace the copper lines on the board when pictures are not clean and clear. We are doing long distant troubleshooting without having the board in front of us, so good pictures are very important.

[cyclones]

I will try to get better shots of the front and back of the board. In the meantime, I have checked the DZ on the front of the board and they all measure about 600-700 ohms in the forward direction except for DZ901, which was much lower, I think around 20.. it looks different than the other diodes. Previously I was having trouble because there appears to be a thin coating of something on the back of the board, but touching it with the soldering iron solves that problem. None of those diodes seem to be open. I also checked surface mount diodes on the back of the board and all have about 600-700 ohms resistance.

Also, could someone tell me what the blue component labelled RZ901 is and what it's for, and also the yellow block capacitors.

I will be back later this evening with better photos. Thanks.

[cyclones]

I updated the photos.

[budm]

RZ901 is more likely to be surge protection device if the line voltage goes over 140Vac which will cause the fuse to blow. The yellow cap is connected across the AC line for noise filter so it will reduce the noise from the motor from injecting the noise back into the AC line.
Did you have a chance to check the DC voltage on the electrolytic caps yet, be careful since you will be working on the line voltage, do not touch any traces with your hands or body.

[cyclones]

I have not checked voltage on the electrolytic caps. I'm not too keen on working on this "live" without an isolation transformer or some other safety equipment. The electrolytics should be good as they are new panasonics. I did check out all the diodes and the reddish-brown film capacitor -- the monster one -- and all can pass current. Everything was looking ok, but on the back of the board, there are some surface mount transistors. They are all labelled J3Y or 2TY. These are in the lower right of the photo of the back of the board. The top pair seem to check out, the middle pair seem to check out, but the bottom pair I cannot get any continuity between any two leads in any direction. I even touched the solder joints with the iron to try to burn off any coating. Still nothing. Not sure what the function of these is. I tried to trace the lines and found it appears to go to the paper switch -- on the front, there are three leads labelled "paper 2" which go to a switch mechanism that detects paper being placed in the shredder.

[budm]

That large brown cap is part of drop down the power supply (it uses Xc of the cap to drop down the voltage), I can see a couple Diodes connected to the out put side of that cap, it should go to electrolytic cap. I could not trace the board too well using your pictures because I need to look at the component side , then the soldered side back an forth to see how components are connected together.