Am I correctly testing 25V AC on this Atari Powerblock

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Am I correctly testing 25V AC on this Atari Powerblock

The attached image for P5 connector shows pins 4,5 & 6 with 25VAC, 25VCT and 25VAC.

So in testing, I should get a reading from pins 4 & 6 @ 25V, and with pins 4 & 5 and 5 & 6 it should be half, so 12.5V?

Thanks.
 

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HINT: this is the centertap that provides 48-50VAC to a K6100 monitor. :)

HINT:

trans64.gif
 
AC ... then get rectified to +/- DC on the monitor. MAGIC NUMBER: 1.414 :D:D

Danke.

I know the monitor is all well and good (G0719). Going to go through all voltages tonight in Monte Carlo, something is shutting the game off after 15 minutes.
 
The fact that you weren't getting +/-24V on the +/-22V test points on the AR is the main clue you should pursue first. (I think you said you were only getting 17V on one side.)

If I were you, I'd pull the +12V and -5V regulators on the AR, then measure the +/-22V test points again. If they aren't at +/-22V or more (and the same), then the issue is either in the brick, or it's the rectifying diodes or filtering caps on the right side of the AR.

(Actually, you could probably just unplug the J10 connector first, instead of desoldering the regulators. The 36V AC comes in through J9, and leaves as the output voltages on J10, so if you unplug J10, and measure the +/-22V test points, that'll give you the voltages with the load of the game board removed.)

If they are the same, then the issue is somewhere downstream, where either one of the regulators is bad, or something on the game board is drawing too much current, and pulling the supply down. But the first step is to figure out if the issue is upstream (brick) or downstream (game board).
 
Yep, I was going to get all of this to you before responding back to pm, then had a brain fart on this. :)

Thanks!

The fact that you weren't getting +/-24V on the +/-22V test points on the AR is the main clue you should pursue first. (I think you said you were only getting 17V on one side.)

If I were you, I'd pull the +12V and -5V regulators on the AR, then measure the +/-22V test points again. If they aren't at +/-22V or more (and the same), then the issue is either in the brick, or it's the rectifying diodes or filtering caps on the right side of the AR.

(Actually, you could probably just unplug the J10 connector first, instead of desoldering the regulators. The 36V AC comes in through J9, and leaves as the output voltages on J10, so if you unplug J10, and measure the +/-22V test points, that'll give you the voltages with the load of the game board removed.)

If they are the same, then the issue is somewhere downstream, where either one of the regulators is bad, or something on the game board is drawing too much current, and pulling the supply down. But the first step is to figure out if the issue is upstream (brick) or downstream (game board).
 
To follow up, here's what I got:

4&6 = 27
4&5 = 13.5
5&6 = 13.5

Yeh, it depends if the schematic classifies the AC winding voltage as CT or not. Confusing. Fortunately, Atari schematics define the DC rectified voltage to expect ...

Seems Atari was also playing around with half-wave rectifying vs bridge rectifying where the rectified voltage is different depending also on the turns ratio of the power transformer. Thus we see 25VAC and 16.5VAC and 36VAC variants etc. Also depends on application ... ARII bias vs monitors etc.

And in your case, these voltages are going to the ARII and not a monitor, correct? I could not find specifics in the Monte Carlo schematic. Needless, if so, the 13.5Vac rectified is simply used to pre-bias the linear regulators on the ARII.
 
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