On Jan 14, 20:19, Tony Duell wrote:
> >
> > Hi, I've just been having a go at fixing an old Acorn AKF40 monitor (a
>
> OK.... Is this better known as something else? I don't think Acorn ever
> designed their own monitors, did they?
They used Philips or Microvitecs. I think that model is a rebadged Philips
VGA. There's a stock LOPT fault on one of those, but I'm not sure if it's
the AKF40 or AKF30. One of them also has a stock problem with cracked PCB
under the LOPT, due to poor mounting design.
> > few months shy of ten years old I'm afraid), which makes a screeching
> > sound and fails to provide any display when powered up. Not having done
>
> OK, the PSU is in pain. It's either very heavily loaded, or not loaded at
> all.
I found a page with some stock faults listed:
"Check Horz O/P transistor for S/C. If OK suspect EHT/LOPTX assembly. Test
by substitution. A less common fault is a problem with the over voltage
protection circuit. This is a crowbar type across the 28V supply and diodes
6452/6454 type PHF15 (15V 300mW Zeners) and thyristor 7452 type BT151 can
fail causing a short circuit. These can fail for no apparent reason or a
fault in the regulator circuit causing excessive voltage. If these have
failed remove them from the circuit and disconnect the following. Collector
of the horizontal output transistor to avoid the possibility of excessive
EHT, R3563 feed to frame O/P and R3512 feed to horizontal drive circuits.
Connect a meter across the 128V rail and switch on the unit. If the voltage
is excessive and does not respond to adjustments with R3414 switch off
immediately and examine the regulator circuitry. Transistor 3470 BC558B can
also fail and is best tested out of circuit using a transistor tester. If
in doubt replace it."
--
Pete Peter Turnbull
Network Manager
University of York
Received on Mon Jan 14 2002 - 18:21:13 GMT