Re: New to list, Amplifone questions

On Wed, 12 Nov 1997 11:43:35 -0500 (EST), Dan Rasmussen
<dras@telco.stratus.com> wrote:

>
>Hi Guys,
>
>I'm new to this vector list and would really like to get it
>in digest form as it seems really busy. Is this possible?
>
>Anyway, I have an amplifone questions:
>
>I recently got an amplifone HV board (a white, rev 2 board) for my
>dead star wars monitor. I was told that the board tested good (with
>an hv probe, not in a working monitor) and it came from someone on
>rgvac that I have dealt with before and trust. Anyway, the board
>arrived with a broken lead (aparently happened in shipping) where one
>of the large resistors had been jumpered. There are also other
>modifications to this board that include the addtion of two diodes
>on the solder side of the board. I can provide more details if
>necessary.
>
>I was wondering if anyone knows of a modification to this board
>that includes the elimination of the large resistor at the top left
>corner of the board (as you look at it with the heat sink on top and
>the HV trans on the right, I would provide the location marking from
>the board but it is too burnt to read). This board does look like it
>has been factory serviced (it has several service/tested stickers that
>my original HV board does not have).
>
>I will add that, while the other mods to the board seem to be cleanly
>done, the jumper wire is a mess: Somone clipped the resistor on one
>side, then desoldered the other side. The jumper was then soldered to
>the old resistor lead on one side and to the board on the other. Its
>quite a mess.
>
>One more thing the two boards have different HV transformers though
>both are red.
>
>I figure that I need to either replace the broken jumper wire but I
>hesitate to do so if this is not a known modification to this board.
>Maybe I should just restor it to its original configuration.

The diodes are legit, I have three (or four?) amplifone boards and they
all have factory installed mods that include a couple of diodes. I
haven't looked at the schematic, but I imagine they bypass the
regulators to keep them from blowing during power up/down transitions.

Also added to the HV section of all amplifones are a couple of 50 ohm
power (3 or 5 watt I think) resistors that are connected across the
voltage regulators. These were added to supply the additional current
needed during the explosion scenes in Star Wars, where the screen goes
white. During the explosion HV regulation will suffer, but hell it's an
explosion, who cares if the screen jumps around a bit?

If it is one of these resistors that was bypassed, then loose the
jumper. It probably indicates the regulator died and this was a shlock
job at trying to get the board going without replacing the regulator.

-Zonn

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Received on Wed Nov 12 10:37:57 1997