Field Change Order: E011
Date of Issue     : October 1987
Applicable to     : A305,A310,A440


Reason for Issue:
To reduce video Noise


Types Affected:
Check all early boards for modification.

   
Description of Change:
See attached sheets


Claim Procedure:
Following completion of the field change order instructions, service
engineers should fill out a service report clearly stating the serial no. of
the host unit, the FCO no. (above), and claim the FCO credit rate (below)
for labour charges. Any replaced components should be wrapped to ensure safe
carriage and returned with the service report. Acorn will verify the
information and, process the claim for labour charges and issue any
replacement components as necessary.

Rework Doc. Reference:
N/A

FCO Credit Rate:
£5.00 (Five)

Special Instructions:
See attached sheets

Remove the circuit board from the computer.

Identify IC17, the VIDC chip. This chip is the closest of the four main
chips to the back panel. Further towards the back of the computer you will
find R67. This is the nearest to VIDC of a whole row of resistors. Take a
1N4148 diode, form the leads and crop them so that the diode can be
connected parallel to R67. Solder the diode to R67 so that the cathode (the
end of the diode with a dark stripe) is next to Q13 - i.e. closer to the end
of the board. 1N4148 diodes are widely available, for example Farnell stock
then as part number 1N4148, or RS part number 271-606.

The second part of the work instructions vary as to whether or not you have
vacuum de-soldering equipment.

Identify the decoupling capacitor (marked 'A') that is closest the the VIDC
chip towards the back of the circuit board. This is also close to Q12. If
you have vacuum de-soldering equipment, de-solder this decoupling capacitor.
if you do not, crop the legs of the capacitor such that you can solder to
the removed legs on the circuit board. Fit a 22mF axial lead electrolytic
capacitor, working voltage 6.3v or higher to the circuit board in place of
this component. If you have de-soldered the previous capacitor, you should
fit this capacitor in the location of the removed de-coupler, otherwise,
solder the legs of the new capacitor to the remaining legs of the decoupling
capacitor. Note that this is a polarised component, and you will need to
observe the polarity. The +ve connector should be made to the connector
closest to R68 and 69, and the -ve connector should be made closest to Q12.
Farnell's part number 030 34229 is a suitable capacitor.