7603/7L13 character display problem


Jordan
 

I'm sorting through some problems with my 7603/7L13 SA module.

Aside from finding some of the worst solder connections I've ever seen on the Sweep board, I have a few issues with the text display which may or may not be related to the bad soldering, which appears to have corrosion on the pads.

If I understand correctly, the top and bottom lines of on-screen text is generated by the 7603 mainframe which is fed with logic signals from the 7L13....Is that correct...?

What could cause the display to show a series of numbers in the center text where the video filter BW should be displayed, and similarly, what would cause incorrect characters on the top line...?

Eg...where the display should read say Mhz, it reads Mhy with a decimal point following the y...

I'll try to post some pictures once I figure out hot to upload pics on here...

Any help would be greatly appreciated....73...Jordan...


Dave Casey
 

Jordan -

The readout works by the mainframe sending current pulses to the plugin and
measuring what happens to them. The plug-in provides different resistances
to select the characters. The 7603 readout is divided into 6 fields, a top
and bottom field for each slot. Since the 7L13 occupies all three slots, it
can use any of the fields. If readout works fine with other plugins in the
affected slot (you can put a 2ch vertical plugin like the 7A26 in any slot
to test), then the problem is probably connections or a bad resistor in the
7L13.
Readout problems are also often caused by the slot connectors on the
mainframe side. If wiggling the plugin affects the readout, you likely have
this issue.

A more detailed explanation of how the readout works can be found in almost
any 7k mainframe service manual.

Dave Casey

On Fri, May 28, 2021 at 12:04 PM Jordan <Outposter30@shaw.ca> wrote:

I'm sorting through some problems with my 7603/7L13 SA module.

Aside from finding some of the worst solder connections I've ever seen on
the Sweep board, I have a few issues with the text display which may or may
not be related to the bad soldering, which appears to have corrosion on the
pads.

If I understand correctly, the top and bottom lines of on-screen text is
generated by the 7603 mainframe which is fed with logic signals from the
7L13....Is that correct...?

What could cause the display to show a series of numbers in the center
text where the video filter BW should be displayed, and similarly, what
would cause incorrect characters on the top line...?

Eg...where the display should read say Mhz, it reads Mhy with a decimal
point following the y...

I'll try to post some pictures once I figure out hot to upload pics on
here...

Any help would be greatly appreciated....73...Jordan...






Jordan
 

Hi Dave...

Thanks for that info, it helps me understand the text display process so I can figure out where to start getting this SA back in service.

I've had some problems with the cam driven contacts which I've corrected at least temporarily while I resolve the displayed signal losing lock at 50khz and lower bandwidths...Then I can work on the display issues...!

Thanks again, 73...Jordan...