TDS 420 serial issues.

[marshkillz]

I got a TDS 420 from someone on craigslist who sold it to me dirt cheap (10$) with some other test equipment with the complaint that it wouldn't turn on.
After doing some troubleshooting and adjusting voltages I got the thing working, but with no trace, which turned out to be the DSP card which cost 60 for a new one.

Which leads me to this point, Ive been trying to enable options that were lost via the serial debug port on the CPU card but I cant get anything but garbage back.

Below is an example of what It returns while booting.

fb d4 ca 94 b4 af 2f 3a 0a ca 4a ca f5 3a 9a 55  ûÔÊ”´¯/:.ÊJÊõ:šU
da d4 9a 6a f4 1b 1b 1b 1b 1b 1b 1b 1b 1b 1b 1b  ÚÔšjô...........
1b 1b 1b 1b 1b 1b fb fb d4 ca 94 b4 af 2f fa 54  ......ûûÔÊ”´¯/úT
74 b5 ea 8a da f5 ba ba 55 ca 74 f4 1b 1b 1b 1b  tµêŠÚõººUÊtô....
1b 1b 1b 1b 1b 1b 1b 1b 1b 1b 1b 1b 1b fb fb d4  .............ûûÔ
ca 94 b4 af 2f fa 54 74 b5 ea 8a ea 9d 3a 6a 8d  Ê”´¯/úTtµêŠê:j
ba ca f4 1b 1b 1b 1b 1b 1b 1b 1b 1b 1b 1b 1b 1b  ºÊô.............
1b 1b 1b 1b fb fb d4 ca 94 b4 af 2f fa 54 54 d5  ....ûûÔÊ”´¯/úTTÕ
6d 0a 2a 3a b5 da ba b5 ea 8a fa 1b 1b 1b 1b 1b  m.*:µÚºµêŠú.....
1b 1b 1b 1b 1b 1b 1b 1b 1b 1b 1b fb fb d4 ca 94  ...........ûûÔÊ”
b4 af 2f ea 3a 3a b5 da ba d5 9a ea aa 74 ba 94  ´¯/ê::µÚºÕšêªtº”
a5 fa 1b 1b 1b 1b 1b 1b 1b 1b 1b 1b 1b 1b 1b 1b  ¥ú..............
1b 1b fb fb d4 ca 94 b4 af ef 53 f4 34 85 da ca  ..ûûÔÊ”´¯ïSô4…ÚÊ
aa ba da 55 ca fa 1b 1b 1b 1b 1b 1b 1b 1b 1b 1b  ªºÚUÊú..........
1b 1b 1b 1b 1b 1b 1b 1b 1b fb fb d4 ca 94 b4 af  .........ûûÔÊ”´¯
ef 53 f4 34 f6 2c e9 d7 56 ab 2a ba 55 ca 74 f4  ïSô4ö,é×V«*ºUÊtô

Any ideas why the serial port would be messed up like this?

[Tomorokoshi]

Look up the TDS 420 and similar Tek scopes of that vintage for electrolytic surface mount capacitor failures. There may be circuits failing because of that.

[Tomorokoshi]

Some starting points:

http://www.antiqueradios.com/forums/viewtopic.php?f=8&t=243742

https://forum.tek.com/viewtopic.php?t=136193

https://www.eevblog.com/forum/repair/textronix-tds-420-repair/

[charlyd]

create a console adapter and run the debug boot to see what is really happening. and yes can be lots of CAPS.. and tracks & pads.

[marshkillz]

I already went through replacing all the caps when I originally had the DSP fault which ended up not fixing the original issue.

The message I posted as an example is what shows up on the serial debug terminal when booting. The scope seems to work perfectly fine except that it doesn't seem to be communicating correctly over the serial debug port.