ASCOM SE550 Replacement Manual

ASCOM SE550 EPROM replacement and tune-up

Disassemble the set

• Remove the code plug.
• Remove the microphone.
• Unscrew the socket cap head screw at the bottom of the code plug socket.
• Remove the front panel by hinging the code-plug/microphone end of the panel
towards you.
• Remove the four screws holding the front AF/Logic board assembly to the case.
• Remove the four screws holding the rear RF board assembly to the case.
• Remove the RF and AF/Logic assemblies from the case.

Replace the EPROM

•
Remove the screening can cover from over the CPU, RAM, and EPROM on the
AF/Logic board
N.B. The can is often soldered at the corners careful levering will normally break the
solder joints
•
Remove the old EPROM and insert the new EPROM.
N.B. Make sure that all the leads of the new EPROM actually end up in the sockets -
it's easy to bend a lead and wrap the lead under the EPROM
•
Replace the screening cover - solder at one corner if there are no positive location
dimples to hold it securely in place.

Assemble the set without the case

•
Plug the RF and AF/Logic boards together without the case.
N.B. Take care that the pins between the two assemblies and the front panel are
correctly aligned!
•
Insert a code plug - or a jumper across the bottom two pins of the code plug socket
•
Insert a microphone
•
Connect power and loudspeaker.

Switch set on and test basic function

•
Press the power button BRIEFLY
The set should power on, beep and display 70.000.000 with the error light lit.
N.B. If you hold the button too long the set will immediately switch off! Do not wait
for a beep or the display.
•
Open squelch, by pressing the appropriate button.
Check that audio sounds OK (lots of white noise) - if not double check loudspeaker
connection and mating of front panel to main set (e.g. bent pins, pins in wrong holes!)
•
Check operation of buttons.
S.Tompsett 1 4/9/2006