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Advice on how to repair vt320 transmit data

munocat

Member
Joined
Jun 27, 2019
Messages
29
Location
Vancouver WA
I recently got a vt320, it is amber, and I have always wanted an amber. The problem is the serial communication receives, but does not transmits. The cable has been tested on a second vt320 (sadly this is white). I am no electronics expert, but I can solder.

Any advice on where I should look. Dissembling the CRT from the board is very daunting.

Thanks in advance.
 

Alegend

Experienced Member
Joined
Jun 13, 2017
Messages
59
Location
Israel
Hi,

If disassembling (then somehow fixing, then re-wiring) a PCB in the faulty VT320 is too much trouble, perhaps just do a swap.

I did a VT320 CRT transplant in the past and posted a manual. Maybe if all you want is a working amber VT320, just go ahead and swap the CRTs. No soldering involved.

http://microvax2.org/wp/2017/05/24/vt320-crt-replacement/

Good Luck,
-Alon.
 

kgober

Veteran Member
Joined
Mar 19, 2017
Messages
626
Location
New Jersey, USA
did you try swapping keyboards with the working VT320? maybe it transmits fine but the keyboard subsystem is faulty?

or did you verify no transmit by sending the VT320 an escape sequence it would be expected to send a response for?

if it's really not transmitting, the usual suspect on other systems is the RS-232 line driver IC. 1488/1489 were very common chip numbers for line driver/receiver chips. if you trace the transmit pin wiring/trace back on the circuit board, the first chip you come to will probably be the line driver. If you can find the VT320 field service manual on-line that should help, but I am travelling currently and don't have time to search myself.
 

daver2

Veteran Member
Joined
Jun 19, 2012
Messages
9,336
Location
UK - Worcester
Don't forget that there are also a lot of configurable parameters stored on the terminal itself.

You should check that you have the non working unit setup the same as the working unit.

Dave
 

munocat

Member
Joined
Jun 27, 2019
Messages
29
Location
Vancouver WA
Hi,

If disassembling (then somehow fixing, then re-wiring) a PCB in the faulty VT320 is too much trouble, perhaps just do a swap.

I did a VT320 CRT transplant in the past and posted a manual. Maybe if all you want is a working amber VT320, just go ahead and swap the CRTs. No soldering involved.

http://microvax2.org/wp/2017/05/24/vt320-crt-replacement/

Good Luck,
-Alon.

Thank you, I tried to swap the whole crt unit across. Just got a blank screen.

Don't forget that there are also a lot of configurable parameters stored on the terminal itself.

You should check that you have the non working unit setup the same as the working unit.

Dave

I check setting, configured the same as the working unit.

did you try swapping keyboards with the working VT320? maybe it transmits fine but the keyboard subsystem is faulty?

or did you verify no transmit by sending the VT320 an escape sequence it would be expected to send a response for?

if it's really not transmitting, the usual suspect on other systems is the RS-232 line driver IC. 1488/1489 were very common chip numbers for line driver/receiver chips. if you trace the transmit pin wiring/trace back on the circuit board, the first chip you come to will probably be the line driver. If you can find the VT320 field service manual on-line that should help, but I am travelling currently and don't have time to search myself.

I took the logic board out. I see there is a browning around a Transistor.

Have the setting correct?
Use local echo (turn it on in the setup menu)
so you can visualy see if the keybord is working on the screen.

Then check all the setup communications.
Compair with your working display.

Here is a Installation book VT320 a PDF-File

Or throug VT100.net HTM-web

Thanks for link.


Update:

I found someone selling logic boards on eBay. They were asking a lot, more than buying a whole working unit. I contacted them with an offer. It is now in the mail.

Thank you too all. I am tempted in replacing that transistor and seeing if it fixes the fault.
 
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