2PAC Mafia
Member
No, it´s new and it measures right, 0,7V...
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Definately a startup-only problem then...
I know that you've already checked the resistor chain R121/R155/R122/R156, but it might be worth double-checking by measuring the (AC) voltage accross each resistor with the mains on - make sure the voltage is the same accross all resistors.
Is it possible that something's shorted near R157 that could be pulling the voltage down at the junction of R155/R122?
I doubt that it's important, but what nominal mains voltage are you on - 110 or 230?
Those voltages look about what I would expect. Can you check the voltages across R106, R107, R109 and R150 while the circuit is trying to start. I would expect the reading to be zero. When you forced the circuit to start were the output voltages correct. (I think about +/- 25.5 on V+ and V- and +/- 10 on +/- VCC) ?
Les
Measure the voltage across the resistors with power applied but with it in the sate were it should start. I do not believe there should be any voltage across them until the supply is running normally I'm just looking for thing that could be drawing current from pin 12 of the IC. Measuring the voltages after you have forced it to start was to see if it was working perfectly once started. I was particularly interested in V+ and V- (The output ends of L201 and L202) This is to see if the voltage regulation of the switched mode part is working correctly. If it is not it may direct us to the start problem via a different route or give us a clue in some other way.
Les.
I guess that the AC on R109 must be just leakage through ZR101 and/or being sourced from the IC (a bit of pulling up?) through D105... remember it'll be "pulsed" or very ripply DC on pin 12 of the IC, as C118 charges from the mains and is then discharged by whatever our mystery current sink is.
If there's more voltage on R150 (681 ohms?) than on R106, doesn't that indicate a lot of current flowing out of pin 7? That seems very odd. Or could it be flowing through the gate of a damaged Q103?
Your measurements in #23 give a current of about 370uA (RMS) - which should be enough to start the IC, which has a maximum startup current of 250uA, according to the datasheet. I'm probably mistaken here, but shouldn't these add up to 230V, not 130?