Amplifone HV Trouble (Star Wars)

[Moortus]

Hi,

I have Dez's HV board and an original, rebuilt deflection board. The had the display looking sharp, bright and rock solid. I noticed something go wrong with the display the other day. The screen size shrank equally about an inch around all four sides and the text and other vector element now wave about a bit on screen. I checked the HV on the tube and it was reading 22KV when it was previously dialed in to 19.5kv. I tried to turn it down but the HV pot mechanically could only take it down to 20.83KV. I noticed as the game plays or goes through attract mode the HV dances around from 19.53Kv to 20.85KV. It used to just sit at 19.5KV with hardly any change. Something is not right, but I don't know where to start looking. Any ideas?

Here is a video of the text waving problem.
https://www.dropbox.com/s/l54agozqosd2mbk/IMG_0724.MOV

Thanks,

Carlos

[dezbaz]

The neg regulator is a good start.

It's meant to lock in 24V (neg) between GND and "O" of the reg, under all loads

If it's not, it needs replacing

In the email you mentioned it was at -30V DC

[Moortus]

I took the -Neg Regulator (7924) out of the circuit and measured voltages where the regulator was... Side hole(GRND) Center hole(-33.79) Side hole(-23.8)

[dezbaz]

Originally Posted by Moortus

I took the -Neg Regulator (7924) out of the circuit and measured voltages where the regulator was... Side hole(GRND) Center hole(-33.79) Side hole(-23.8)

The reg is needed. So the test result here not really needed

I suggest pop a new one in and see if it locks to -24V on the output

Use an insulator and heat paste etc

[dezbaz]

Same kinda thing being discussed here

http://forums.arcade-museum.com/show...&postcount=414

IE from post 414 on . . .

[ArcRevival]

Put it in test on the green diamond screen and see if your HV fluctuates, it almost always fluctuates in gameplay mode.

[Moortus]

The picture fluctuates in test mode and all screens even the green cross hatch screen. The picture was steady in test mode and in the game for a month after I built Dez HV board. Then one day the screen size shrank by 1 inch all around and the video was fluctuating. I checked the negative regulator on the HV board and the voltage was -30 and -31 testing the ground leg to the other legs. I have some 7924 regulators on order. We'll see if replacing the negative regulator fixes the problem.

[ArcRevival]

The picture may be fluctuating in test but is the voltage fluctuating with it ?

[Moortus]

The HV fluctuates up and down from between 19.53KV to 20.85KV . The first month after I built the HV board it was dialed in at 19.5KV and would stay there throughout every screen in test mode and while playing the game. I didn't have a DMM on it for a whole month but the first cople of days I did and it barely moved +/- .01 from the 19.50KV setting.

[ArcRevival]

By the way, instead of measuring the HV, measure the B+ instead and see what's it doing.