Yes, correct again, switching poles I measure 28.9M, thanks Minkok!
About not touching the board as much as I can: That is probably the best advice lol! But where's the fun in that? Let's wait and see if I can get a functional soldering station with this board's help. I mean, if I can do it that would mean anyone could ;-)
ok, I managed to thread thin copper wire through the vias and thus connect Q2 and Q8 to the back of the board. Result: I measure 3.3V and -600mV at J3. Yay!
So, next up is to replace Q1, R8 and R18. Just curious: What do R8 and R18 influence?
[quote author="minkok"]How you measure it? multimeter on Vdc is it? and you measure over C1. next: Disconnect power and measure on diod test- black probe at C1- GND, red over the fuse and tell the result, leave removed components out.[/quote]
Oh my, how can I be so stupid? The meter was on Vac all this time... I will go and hide in a corner now...
C1 measures 23.8Vdc. I will re connect all removed components tonight and re-measure. Q2 will be a challenge and probably will require a wire to the back of the board as the via pad now is almost completely gone. All because of my stupidity. I will probably end up building a new back board from scratch.
edit: wat about R8 and R18? They are obviuously mislabelled and need to be replaced by resistors that actually measure 30k instead of 15k, but are they of influence in this particular issue I am trying to solve,?
I do not see any black spots in person but Q1 does fail the continuity test on the right pin to the top pin, that's not good is it? Also, U1 has continuity between a number of pins in the middle, is that a sign it is fried as well? No other components seem damaged.
Edit: I temporarily removed D6 but it made no difference to VC1. Still around d 11,5V.
Edit 2: Q7: Continuity between pin1 and top pad. Bad?
Afedorov, Minkok: thanks for the pointers. As you will have guessed I am dependent on experts like yourselves to point me in the right direction, so thanks again so much!
I am connected to AC, so that's not it. I will follow up on your tips and report back. I'll post some pictures too.
[quote author="minkok"]Hello Doomedahab, first disconnect the front board and check again C1 voltage and if it the same, check fuse, if D1 to D4 are correct positioned, if you connect Trf. to J1 and remove TVS temporary to measure Vc1.[/quote]
Thanks Minkok!
All measurements were without the front board attached. D1-D4 are oriented correctly. I already inspected the fuse, and replaced it to be sure. The fuses look undamaged. It's a clear glass version with a thin wire so it would be easy to spot if it would have popped. There is however virtually no voltage across its terminals.
Ok, so tonight I tried to power up the back board. It turns out that my toroidal transformer actually puts out 27.2 volts at 238V mains voltage. Is that to be expected for a 230v, 120VA, 24v transformer?
Anyway, I connected the board to the transformer, and unfortunately I do not get correct readings when measuring at J3. between the 3.3 pin and gnd i read 0.02 volts. Not good.
Some measurements I took:
across the TVS: 11.42V across the diodes: 14.98V C1: 11.52V I tried a few other C's but they read fractions of volts at best.
Can anybody give me some advice as to where and what to measure next to find the root cause?
I did have to solder Q2, Q8 directly to the vias (see a page back), but they do not appear to be shorted when doing a continuity test. would these mosfets be a possible cause of the bad readings?
I tried briefly, but the smooth stainless casing is proving hard to solder to. I might try again after maybe sanding the case slightly to make the surface more rough. But for now I will leave it if it's not critical.
