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This machine which is 8 years old has been trouble free so far but a couple of days ago when going to start the machine it showed no display or button functions working. Tried a reset – nothing. The last use it had it worked fine and no water remaining in bottom of machine etc.
As there is no functioning display then its impossible to know if there are any error codes
I have conducted the main checks I could and looked at every post I could find on the topic without success. Have gradually dismantled the DW to check components and wiring and so far at a loss to find anything failed or burnt (including on both PCBs). The large resistor on the Control module is not burnt or open circuit and measures in at 100ohms, the TNY264GN appears physically good but cant test it as I dont know the outputs to look for. Have tested both electrolytic caps on this board and they are fine. The control module does not appear to have any fuses of its own.
The board receives 240v (lathough thi sshows as 125v on each of the two incoming pins and shows 240v on many of the main connectors on the board ( one wire to ON/OFF switch gets 240v and the other gets 125v which converts to 240v when On/Off button pressed. This 125v to 240v on the switch circuit does not seem to latch when the button is released but that may be normal ?. Can’t hear any of the 6 relays clicking and there are no lower voltages (AC or DC) on any of the other connector outputs at all.
What I have noticed is :
1) Both plastic tanks on each side were nearly full (don’t know if this is normal when a machine finishes its cycle)
2) I can get no continuity readings through the yellow wiring going from the door switch sensor to control module and back to the module – whether the door is open or closed (but no idea how the sensor works – I thought it was magnet operated). So not sure if this has failed somehow and has locked a restart or reset!!
3) No leaks anywhere inside or outside the DW and drain is completely clear and drain pump not clogged and is turning freely.Anyone know how to test the TNY chip and how to test the door switch sensor?
Any thoughts would be very gratefully received as I am now at a loss as what to do next.
Regards
Johnthe tny chip lowers the voltage for the board so it gets 300v DC in and probably 12V DC out
if you look at the board around the chip you will see varous electrolytic caps, look at the working voltages. stay well clear of the 300v ones and look for one in the 35 to 35V range. then test across these for voltages.
be very careful as this has to be done live. I suggest you add some insulation tape over the high voltage connection as a temp safety measure
if you want to be ultra safe solder some wires either side of the cap ans measure off the board
if you dont know if you can do this safely dont tryDave
Hi Dave
Thanks for the quick reply. Not an electrician by trade but spent many years fixing Monitors, TVs and many other PSUs so well used to working with the voltages found on these boards. The blue 300v caps that surround the chip on this board aren’t electrolytics (I don’t think anyway) and I cant find any caps in the 30 – 35 volt range.
Will look for a data sheet on the tny chip and see what I can get from that.
I find the door sensor the most puzzling – any thoughts on that as a cause?
Johndoor sensor is a simple reed switch The switch is in the door and the magnet is in the frame
though i had a pic of a bosch board. The plug has been removed on this one it burnt out
HV cap is the big one. the little one should be LV out
also check diodes as we get Shotsky diodes shorting on some units
DaveChecked both of those caps and both are good – ie gave the correct uf reading. Will check the blue caps tomorrow.
So if the door sensor is a reed switch and I get open circuit with the door open or closed surely the reed switch in the sensor must have failed?you need to check voltages on them. big one will be just over 300 but the small one is the output from the tny chip. so if this has 12v or so on it then the chip and power supply are ok
The blue ones are x2 supression caps, if they fail thing just short out. one is L to N the other L to EDave
Will check the caps as suggested. Do you agree the reed switch in the sensor must be failed? – and can that affect the boards (especially the LED display and buttons) firing up?
can be easily checked with a magnet and a multi meter
but may stop display but wont stop it powering up as far as i know
Dave
Hi Dave
Tested some of the components you asked for above ( see photo – BUT this is not my board and shows faulty components so ignore those as mine has none of those faults evident)
The large cap shows 328 volts but the small cap shows 0v.
The tny shows 328v at its input but all other pins show 0v
The small coil which ( in my ignorance) seems to be the feed for the small cap shows 328v on one side but 0v on the other side.
All the diodes I could identify tested OK ( but that is in circuit).
Have not retested the door sensor as yet but I am fairly sure that looks faulty by previous tests.
Any thoughts on the above findings or ideas on further test to do.
Many thanks again for all of the help
JohnPhoto wont upload even when I reduce its size as I get a message saying only have 1.1kb left for user group??
host photo on another site like google pics and post a public link
i would change the TNY chip and see what happens
dave
Here is a link to the photo (hopefully!!)
If you get this can you tell me what the coil does and why it could have 328v on one side but 0v on the other pins?cant see pic but the coil is a transformer
if the chip is not oscillating then its dc and transformers need ac
Dave
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