No +20v & Testing Diodes

[Lippy427]

Hi All,



Just looking at a problem on my CV - no +20 Volts and F107 blowing.



I've had a look on the old pin repair site with regards where to look, what to test (and how), and have just tested the diodes D7 - D22 on the power driver board with the following results...



Testing with the DMM set to diode, all diodes read between 0.65 & 0.83 with the exception of one (D18) that reads zero (in both directions). Now I'm fairly happy that D18 is shot (it buzzes out in both directions also) and that this is the problem with the +20 Volts, but I'm not sure about the others - 'marvins' states that they should be between 0.4 & 0.6. Also, some of the diodes take several seconds to settle on constant reading - with a few starting with a -ve value.



Is 'marvin' correct and should I be concerned? Should I replace all the diodes just to be sure, or are the readings OK?



Any help appreciated.



Cheers

Geoff

 

[Adam]

Sounds to me like it's only the one diode that needs replacing, swap that one out and go from there.

 

[Moonraker]

yeah, don't forget that diode values can still show different amount whilst they are still connected because of other things in the circuit. I'd say 0.65 & 0.83 look good without taking them out of the circuit. Deff chnage D18.

 

[pinballmania]

Agreed. The negative readings are caused by the charged capacitors in the circuit. You can discharge them by shorting their terminals. The diode readings look fine on the diodes

 

[Lippy427]

OK, thanks for the replies guys - I'm off to buy me some diodes