VT100 to VT103 conversion

[hush]

hey all! i recently picked up a spare VT103 backplane on ebay thinking since they (VT103s) are quite rare, it might be possible to retrofit it into my VT100- as far as i know they are the exact same physical dimensions and all, just the power supply is beefier and there is an LSI11 backplane. that being said, i am not sure if there are any pitfalls that i should be aware of. apart from the stronger power supply (which can be provided via ATX conversion until i can find a genuine model), is there anything that i should be aware of? has anyone tried this before?

thank you!

 

[Schroeder]

Not sure if VT103 are really rare, maybe they are kind of customized like mine which was used at a aircraft maintenance factory. It has an additional serial breakout box. I can take some photos when I'm back home.

 

[hush]

anything you can provide would be very useful, thank you!

 

[jasperwilde09]

Hey, so if you're thinking about swapping out the backplane of your VT100 with one from a VT103, you might want to think twice. Here's why:
1. Electrical Stuff: personality test
So, besides the obvious difference in the power supply, there could be other electrical variations between the two backplanes. If the voltages or current requirements don't match up, you could end up frying some of your VT100 components. Not cool.
2. Functionality:
The backplane in the VT103 is designed for specific functions that your VT100 might not have. So, trying to make it work could lead to all sorts of weird behavior or just straight-up malfunctions. It's like trying to fit a square peg into a round hole – it's just not gonna work smoothly.

 

[saipan59]

Hey, so if you're thinking about swapping out the backplane of your VT100 with one from a VT103, you might want to think twice. Here's why:
1. Electrical Stuff: personality test
So, besides the obvious difference in the power supply, there could be other electrical variations between the two backplanes. If the voltages or current requirements don't match up, you could end up frying some of your VT100 components. Not cool.
2. Functionality:
The backplane in the VT103 is designed for specific functions that your VT100 might not have. So, trying to make it work could lead to all sorts of weird behavior or just straight-up malfunctions. It's like trying to fit a square peg into a round hole – it's just not gonna work smoothly.

I had a VT103 that I bought in the 80's via the 'Employee Purchase Program'. It cost me over $4K. I still have the Q-bus backplane from it, but nothing else. It has an edge connector for the VT100 board to plug into.

Check the 103 print set to be sure, but I think the VT100 module (that does the terminal functionality) is the same in a 100 or 103. The difference would be in the cabling for the serial ports - the VT100 board would go to one of the LSI serial ports, instead of to the rear bulkhead. A second LSI port goes to the bulkhead as a printer port.
So, the change from 100 to 103 is really just a bigger PS, and a physical space for the bigger BP (which happens to include 4x4 Q-bus slots).

Also, some versions had a dual TU58 drive as well - that requires a different plastic case that is unique to the 103. But you don't have to do the TU58.

Pete

 

[jasperwilde09]

Hey Pete, thanks for chiming in with your experience! That's really valuable insight, especially coming from someone who actually owned a VT103 back in the day. heardle
You're right, it seems the core VT100 module is the same, and the main difference is the backplane and power supply. That clears things up a lot. I was mostly concerned about potential electrical mismatches and functionality issues, but your explanation about the cabling and the Q-bus slots makes perfect sense.
It's also interesting to hear about the dual TU58 drive option. I didn't know about that.

 

[Hole98]

Hey Pete, thanks for chiming in with your experience! That's really valuable insight, especially coming from someone who actually owned a VT103 back in the day. heardle
You're right, it seems the core VT100 module is the same, and the main difference is the backplane and power supply. That clears things up a lot. I was mostly concerned about potential electrical mismatches and functionality issues, but your explanation about the cabling and the Q-bus slots makes perfect sense.
It's also interesting to hear about the dual TU58 drive option. I didn't know about that.

Original VT103 Brochure showing internals and options here

VT103 LSI-11 Video Terminal

Title : Digital Eequipment Corporation Microcomputer Products Option Bulletin April 1980. VT103 LSI-11 Video Terminal Publisher : Digital Equipment Corporation

classic.technology

 

[reinhardtjh]

Check the 103 print set to be sure, but I think the VT100 module (that does the terminal functionality) is the same in a 100 or 103. The difference would be in the cabling for the serial ports - the VT100 board would go to one of the LSI serial ports, instead of to the rear bulkhead. A second LSI port goes to the bulkhead as a printer port.
So, the change from 100 to 103 is really just a bigger PS, and a physical space for the bigger BP (which happens to include 4x4 Q-bus slots).

Also, some versions had a dual TU58 drive as well - that requires a different plastic case that is unique to the 103. But you don't have to do the TU58.

Pete

I have a VT103, VT103-BA technically since it has the dual TU58 DECtape II drives. I have bought spare VT100 boards from Ebay and can tell you that the boards that came in my VT103 match the spares I bought. The serial interface between the VT100 board and the LSI is done by a special board which plugs into the VT100 STP connector on the VT100 board. That is the big, white connector that sticks out from the board. It is a special design in that when no board is plugged in, the contacts touch each other and complete a standard circuit between the EIA connector on the back and the VT100 internals. The VT103 board plugs into this which interrupts the circuit and brings the serial interface out to a connector on the board which then plugs into one port of a SLC in the LSI. If you look at the cover of the brochure that Hole98 posted you can see the STP interface card on the desk just below the VT103 manual. The ribbon cables for connecting to the SLC are shown there also.

The card is not required as you can also run a cable from the SLC card out to the DB25 EIA connector on the VT100 controller board just like a normal serial interface.