Superboard RS232 transmit ???? Help!

[nama]

It feels like years since I've posted here. I've been busy playing with a lot of other systems, but it's good to be back.

I recently pulled out my Superboard 600 as I finally decided to build up Klyball's 610 board and try to get the Superboard set up with more RAM and a floppy drive (or two).

First I wanted to test out the system and pretty quickly I realised I cant send anything thought the serial port using the SAVE command (LOAD works well and I can receive date no problem).
I stuck the scope on the transmit (Tx) pin of J1 and was seeing nothing. The system would sit there and wouldn't do anything if I pressed any key.
After some playing around I realised if I touched the collector of Q1 with my finger in just the right way I could see some kind of data on the Tx line when I pressed a key, and as I suspect is normal behaviour, that key was mirrored on the screen too. However still no data was getting to my PC running Teraterm. If I removed my finger the Tx line would stop showing any activity at all.

I connected the scope up to the Collector (Green trace - see image), and to the Base (Yellow trace). The score was set up as 5v/division. and I took some images (with my finger also on the collector (otherwise it wouldn't show any activity)

I'm not sure what I should be looking for and if there is a problem with the signals (as I suspect), and if I should suspect a bad transistor (Q1)???...anyway I thought someone here would certainly know.

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[Mark]

From the OSI schematic, it looks like the RS-232 TX could be 0-5V only, or true RS-232 -V/+V depending on the addition of a negative voltage source.
It's hard to make out in the schematic, but it looks like W10 could be opened to allow for a negative voltage source on J3-pin7, Rs232 out is on J3-pin2

Anyway if the signal on the output of U62 pin12 looks okay, check the other end of the 10K resistor connected to the collector of Q1 (or J3-pin7) to see if it's grounded or floating. If floating, then it expects about -9v on J3-pin7 (according to the same circuit used on the OSI500). I've seen people hang a 9v battery off the connector to provide a negative voltage source for a while. You may get by by just grounding it.

600B RS232

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Good Luck!
-Mark

[nama]

Thanks Mark, I'll give it a go this weekend and report back how I get on...cheers

[nama]

Well, I had another poke around today. I really don't know what's going on at all.
firstly, I'm also not quite sure what the behaviour on the Superboard should be when I execute a SAVE command. I'm assuming whatever is written to the screen ALSO gets sent to the serial port.
So in general after executing a SAVE, I can't do anything. The machine just sits there and no amount of key pushing shows any thing appearing on the screen or any activity at U62 pin 13. However, as I mentioned before, if I put my finger on the traces near (or even touching) Q1 (see photo attached for the area), then suddenly I start seeing activity at U62 pin 13 and also further down the chain from there, and also the Superboard now has characters appearing on the screen. However I'm still not getting what looks like a correct looking signal at the J1 connector and nothing appears at the PC terminal. The voltages at J1 seem to be 5v peek, with the low being about 1/2 volt below that!!!
I've tried cutting W10 with no change.
Now I will also say that sometimes, very rarely, the superboard will show activity on U62 pin 13 without having to put my finger on the board, but that is usually short lived.

Anyway, I'm a bit flummoxed!

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[nama]

I should also mention that the collector of Q1 is at about 2.5V with pulses at about 5V when 'data' is being sent...of course that is with my finger on those traces to get it do do something.
J3 pin 7 is at GND.
I believe the 10k resistor you asked me to check is R64. Seems I don't have R64 installed. I don't even know where it would go if it could be installed.
This page shows some images and talk about how to get serial working. there is an image of what I believe is a rev B board with R64 installed (next to R65). the layout of this board looks a little different than the my rev D.

UPDATE...Grounding J3 pin 9 (CTS) solves the touching the trace with my finger hack ...still no input to the PC terminal though. Output from J3 pin 2 sits at 5V and pulses up to about 6V when sending.

OSI-RS232PartsPhoto.jpg (177.5 KiB) Viewed 6336 times

[nama]

UPDATE...
ok...it's working. After all that it seems to be a USB serial adaptor issue. I have two identical adaptors, and although I was just using this adaptor to connect to a Zeta2 Z80 machine and it was working fine, it doesn't seem to like the OSI. I swapped the adaptor for the other identical one, and it works...Oh well, that was a painful mission. No idea why this USB serial adaptor is so fussy.

...anyway, thank for listening to my ranting!!!!!

Philip