1 Oct
2006
1 Oct
'06
2:58 p.m.
Tony wrote....
Try moving one of the single ROMs into an 'H' socket. Does it still
appear (and work correctly)? Single ROMs can go in any socket, H or L, if
the machine is working right.
> Do you have any other ROMs in the 'H'
sockets? If not, it's possible you
> have a bad buffer chip or something.
I do, but it is only the two rom sets
that use the H sockets that are not
appearing in the PAM list. The roms that do appear, are only using the low
sockets. I think that's not a coincidence. Specifically U5 (74HC245) on the ROM drawer PCB.
Octal Bus Transceiver... I guess there are two of them, one for the lower 8
from the LCD module, which was bought-in, not made by
HP).
and the one at U5 must be for the upper 8? I am not
familiar with that chip.
Is there a relatively easy way to test it before just replacing it?
It's not going to be easy to test in-circuit. If you desolder it, it
should be quite easy to check (grab the data sheet, note that pin 19 must
be low to eneable the chip, pin 1 determines which side is input and
which is output, and then whatever you apply to the 'input' side should
appear on the output side). But if you desolder it, you might as well fit
a socket and a new one.
[...]
(right where the pin becomes narrow). So, I get to try
and carefully
reattach that pin leg to the chip. Can anyone share broken chip leg repair
techniques? I can't attach a tiny segment of wire as a brace - the "socket"
on the board is the type where each pin gets it's own socket so a thicker
leg probably won't go in.
What I'd do is find some wire that will go into the sockets on the PCB.
Put the end into the appropratie socket, then fit the chip and carefully
solder the wire to the stub of the pin.
-tony