Discussion in 'Troubleshooting and Repair' started by bushtech, Aug 21, 2018.
Thanks for clearing that up WHONOES
Whonoes, might make the search easier
whonoes: Sorry for the delay, took a long time to get the parts. Built your circuit and seeing very low voltage there, approx 0.3V. Will be ordering replacement 04N60C3 and the 2f transistor which you identified. Still waiting for my ESR meter to arrive which hampers me a bit.
Anything else I can check to try and narrow things down a bit.?
Just in case I made an interpretation mess, here's a photo. Ignore pink cable has got nothing to do with this detector circuit
If you have removed the 2907 transistor, you could check to see if it is being driven by the control circuit using the detector you built.
Thanks whonoes. In the photo have I connected to the correct legs of the 04N60 C3?
If I remove that transistor do I need to connect somewhere else or do the probes stay where they are?
You will need to connect to the base of the 2907 as that will be the bit being driven (hopefully) though that could be complicated by resistors connected to the base. You might be better off tracing that part of the circuit back to the controller pin and check there for a drive signal with your detector. The 0.3V you saw with your first measurement doesn't sound too hopeful. Is the diode the right way round?
Thanks whonoes. I still have a lot to learn about electronics, so I battle to understand your advice, hence the stupid questions. If I connect one lead to the base of the (removed?)2907 where does the other lead go.?
The diode can be seen in the photo, the banded end points away from the resistor.
@73's de Edd: I still can't see any markings on the 8 pin chip but the 32 pin chip is a ATMEGA88PA.
Sorry for the delay in responding. As the 2907 is a pnp device, the end of your detector that went to the FET gate should got to the Emitter and the end that went to the source should go to the base. There must be no other connections to the detector. Please note that the input resistance of your DMM must be at least 10MΩ if it is only 1MΩ, it will make a considerable difference to your readings.
Thanks whonoes. I now have some 2907's. Shall I remove the old 2907 and then check on the pads on pcb for signal as you now described in your latest post?
I don't understand the bit about input resistance. My DMM goes to 2000MΩ. If I set it to 20MΩ is that Ok or are you talking about inserting some high value resistor?
Apologies for my lack of understanding.
Is there something that I can google for that circuit design you gave me? Does it have a name? I need to understand what I'm doing
No. When you set your DMM to a voltage range, it should have an input impedance of 10MΩ (or 1MΩ). This is a function of the voltage divider in the input stage.
You should be setting your DMM to its 20V dc range.
Sorry, stupid of me, of course we're working with voltages here. But I'm still lost with the input impedances. Do I need to figure out the impedance of my DMM when in 20 V dc range?
It would really help If you could give an answer on this: "I now have some 2907's. Shall I remove the old 2907 and then check on the pads on pcb for signal as you now described in your latest post?"
No you don't need to figure out the input impedance at 20V, it should be the same for all voltage ranges and should be quoted in whatever documentation came with your meter.
Secondly. Yes, remove the old device and then check.
Ah, found it. My DMM's input impedance 10MΩ
whonoes: I have removed the 2907 and as you can see on the photo I get no voltage there. Please have a look at the photo and check if I'm doing this correctly. Power is being supplied via bulb supply. Can the 60W bulb affect the reading?
Checkee-checkee . . . .Is your unit older than its 5 year warranty ???
St. Edd, took it in to the agents who shrugged their shoulders, said too expensive to send back to Sweden or wherever for repair. Out of warranty
Don't know what's happened to whonoes (last seen 11 Oct) so I went ahead and replaced all 3 caps on the hot side including the 2 73's de Edd referred to. I also replaced the 2f (2907) transistor. Then went ahead and pulled the 04N60C3 big heatsinked mosfet. I get a dead short between drain and gate. Is that conclusive that it's fubar?
My two suppliers RS and Mantech both show no info on this 04N60C3 mosfet. Mouser shows it but that's in the US at $1.60. Shipping will make it a very expensive so hopefully I don't have to go that route.
Can somebody please suggest an alternative or tell me I'm wasting my time looking for an alternative.
@73's de Edd :
Just to the 10 o'clock position of your complementary pair of driver transistors for your POWER FET, should be the 8 pin integrated circuit, minus its one pin pulled for board gap HV isolation .
It is being the brains of the control unit for the HOT chassis side .
Can I get its identifying numbering ?
I decided to have another go at this and after fiddling around with graphite, strong magnification and the use of a 1000 lumen flashlight I managed to get: