Re: Quantum/Amplifone HV Blues

Bad R13 (39 ohms)?

Dave Langley wrote:

> Hi ...
>
> I'm in the process of repairing an Amplifone HV board from a quantum.
>
> The game itself is fully working when the HV board from a Star Wars is
> fitted but I'm unsure of the what is happening on the games own HV board.
>
> The board has been recapped, W1 has ben replaced with a solid wire
> link. New regulators and a BU406D have been fitted. Since the red
> HVT was obviously dead due to the HUGE bulge in it I removed it and
> for testing purposes I fitted a 100w lightbulb as a dummy load.
>
> Powering the board up with the dummy load I found that I had +24.5v
> and -25.8v at the regulators. The lightbulb glowed indicating that
> I'm getting some form of output across the input of the HVT. On
> previous encounters with Amplifone HV boards this has indicated that
> all was fine.
>
> Looking at the 20Khz signal coming from the 555 I had a nice square
> wave of about 10v p-p at pin 3 of the 555 and about 0.9v p-p going
> into Q1. This seems fine, however the input to the BU406D is not
> right. I changed Q1 and Q2 but it's still the same. I'm getting an
> odd square wave ... see ASCII art below:
>
> ____ ________ _______
> | | | |
> | _____| | _____|
> | | | |
> | | | |
> - -
>
> On my scope it seems to be a square wave where most of the negative
> going portion is clipped to zero.
>
> At pin 9 of the HVT input (to the MC1)
>
> / | / | /
> |
> / | / | / |
> / | / | / |
> | / | /
> |
> |______/ |______/ |
>
> On my scope it seems to be a sawtooth wave generated when the square
> wave is positive
>
>
> Lastly on 1 of the HVT input (to the BU406D)
>
>
> ___ _____________ _____________
> | | | |
> | | | |
> - -
>
> On my scope it seems to be negative going pulses when the malformed
> square wave is going negative.
>
> Anyway my question is ... is this normal. I'm sure that I've never
> seen wave forms the same as this on previous HV boards and I don't
> really want to risk fitting a new Wintron till I'm sure the board is OK.
>
> (let me know if the ASCII art is no good after Emailing and I'll toke
> some photo's of the signal my scope is putting out)
>
> Thanks in advance for any help.
>
>
>
> Dave Langley
> www.robotron-2084.co.uk <http://www.robotron-2084.co.uk/>
>

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Received on Wed Apr 23 11:44:40 2003