Replacing the Flyback Transformer From My VAXmate
holm at freibergnet.de
Sun May 17 12:52:04 CDT 2020
Rob Jarratt via cctalk wrote:
> I am about as certain as I can be that the flyback transformer from my
> VAXmate monitor board has failed. I know this is probably impossible, but I
> am wondering if there is a way to find a more modern equivalent? How
> standardised are these things? I do see a lot that appear to have the same
> circular arrangement of the pins.
> The VAXmate one is a Tai-Ho TH-1802B and according the Technical Description
> has a primary voltage of +28V and produces auxiliary voltages as follows:
> +13.1kV @85uA max
> +950V @200uA
> +45V @75mA max
> -100V @1.2mA
Rob the Footprints are somewhat standardized, unfortunately the entire
FBTs are not. There are compatible Versions from different
manufacturers, but most manufacturers are gone in the meantime, nobody
want's to look at a CRT anymore...
As most of us, I'm in "historical computers"..and there are several
8-Bit machines that wants to be connected to an CRT Monitor with some
TV related Video input. I have rescued some small 12" industrial-TV
monitors from the dumpster years before und when I needed one lately
I had to fiddle with a defective FBT first.
There are 10pin and 8 pin versions and there are deflection coils with
different impedances, mostly the monitors are to be operated with 12VDC,
but I think in your case I've read something like 28VDC as the operating
voltage of the horizontal output Stage.
My Monitor is working again, I've fitted an 10 pin variant FBT into the 8
holes on the board..with some wire bridges.
I've searched on the hrdiemen.com Webpage, often there es at least an
raw schematic how the coils in ther 2nd source transformers are
connected..and I've crawled trough several monitor schematics to make
the refit work. My Monitor was an chinese model, clearly there is no
schematic available at all...but it can be done.
After the repair I've got 3 small FBTs and 2 deflection coils fromy
ebay for $10, must I say that 2 compatible FBT where in the ebay goods?
I think not...its murphy...
HR Diemens Website has had better times before..don't know how long they
will last. As far as I know there is no direct replacement for your
Vaxmate, I've looked there for that.
You are on your own..sadly as it is.
FBTs from former GDR "Robotron" monitors are all failing now if they
aren't already bad for years. There is an issue with the used potting
material of the HV coil, it shrinks and gets cracks..humidty is
diffusing in and that builds vinegar in conjunction with the for
isolation used polyacetate foil.
There are many people that therefore rewound the hv coil on her own,
it can work..but it is a job for somebody that eats small childrens.
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