5 Jun
2016
5 Jun
'16
11:39 a.m.
-----Original Message-----
From: tony duell [mailto:ard at p850ug1.demon.co.uk]
Sent: 05 June 2016 15:12
To: rob at jarratt.me.uk; General Discussion: On-Topic and Off-Topic Posts
<cctalk at classiccmp.org>
Subject: RE: VR241 Service Manual?
The screen basically works, but it won't go black, it is as if the
brightness is turned up, and I get some diagonal lines when the brightness
is turned up a bit more. I want to know how to take it apart to check the
electrolytics. I have partially dismantled it but I am struggling to take it
apart further, for fear of forcing something and then breaking it.
Does anyone have a VR241 Service Manual?
I have looked on Manx and BitSavers, but there
doesn't seem to be one
available in those places, and a more general search has failed to
turn up anything either.
It's also not in (for example) the VT240 manuals. The VR201 is, but said
manuals specifically refer you to a VR241 documentation set.
What do you need to know? I've reverse-engineered the schematic and can
send you that, but if you do delve inside (a) Good Luck and (b) be very
careful. IIRC there is mains where you might not expect it.
It's a Hitachi chassis, and it shares some feautures with Hitachi
televisions
of
the period. There is a thick-film hybrid module in the
middle of the
deflection
board. It contains the sync/oscillator IC and the
vertical output stage.
The IC,
output transistors and a few other componets are
soldered to the module,
the resistors are thick film traces.
The power supply is evil. It's a switcher, and it runs off the _horizontal
deflection_ oscillator. So for the power supply to run, the horizontal
oscillator, horizontal output, flyback transformer, etc must all be good.
There is a little multivibrator on the PSU board to kick the thing into
life when
you turn it on.
Thankfully the PSU seems OK, but if I can get the whole thing apart I can
check all the capacitors.
Thanks
Rob