Re: Space Duel HV advice

The first thing that has to work after the +/- 27V is the 555 oscilator. It gets its power
from a resistor and zener off the +27V. If the resistor is open or the zener is shorted
(sometimes this happens if the +27V goes way to high) then the 555 will not have it's +15V
supply to run. Check the output of it for a nice square wave.
  This ouput goes through a few transistors, look for it on the collectors of each but
beware measuring the collector of the main drive transistor (the big one), there could be
*large* voltage spikes here. Basically, if the squre wave is not making it to the main
output transistor, then the HV transformer will not be driven with the +27V. The 180V
supply is derived from the collapse of the magnetic field on the HV transformer. You don't
have 180V because the HV transformer is not being driven (turned on and off via the square
wave).
  

"Christopher X. Candreva" wrote:
>
> This game is SO close to working. All we need now is about 19,975 volts.
>
> We've got no HV. We got +/- 25v compliments of the LV2000. We do NOT have
> +180v pin 5 of (whatever should have 180v on pin 5 :-). We have about 25v
> there instead. And we have yet another botched repair by a previous tech.
>
> C905 33uf 160v had been replaced with a 47uf. ARGH. fixed. Several badly
> jumpered broken traces have been fixed. The caps all look to have been replaced recently. The MPSA06/2N3904 have
> not. I've got a bag of MPSA06's and will try to grab an 2N3904 tonight.
>
> The resistors all check out OK in circuit (correct ohmns, no open or
> shorts). I ran out of solder wick last night, but did the diode check on the
> above transistors in circuit. Nothing showed bad, though that doesn't mean
> much in circuit. The transistors mounted to the HV cage passed a diode
> check.
>
> Short of just replacing all the other transistors, any other obivous things
> I should be checking that would cause the 180v to be 25v instead ?
>
> -Chris
>
> ==========================================================
> Chris Candreva -- chris@westnet.com -- (914) 967-7816
> WestNet Internet Services of Westchester
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Received on Mon Oct 18 15:44:37 1999