Retrochallenge 2016 – First look.

151231-IMG_20151231_174248Let’s start at the very beginning. It’s a very good place to start – Apparently.

According to the documentation, the VT180 is a VT100 serial terminal with a VT18X add on board. This add on is a Z80 single board computer that talks to the VT100 though one of its communications ports. this make for quite a nice combination for the day.

You can use the VT100 as just a terminal to your corporate mainframe or mini-computer and when required, fire up the Z80 into CP/M-80 and compute like there’s no tomorrow.

Mine is computing like Yesterday was a little rough.

Onward.

At this point I am working without the VT-18X board present. I don’t think I need it yet. My understanding is that the VT100 side should come up cleanly without it. I could of course be wrong but I’m going down this road for a while.

The photo above shows what I’m dealing with. The keyboard has sensible lights on but I don’t know yet if that means anything.

My first job as always is to try and re-seat all of the socketed chips on the board. I’ve don’t that and it made no difference. Oh well.

Going in.

Next step, are the voltages correct? The VT100 has an Intel 8080A processor on board and that needs care and feeding.

Off with its head.

One thing I’ve always liked about DEC equipment is the way they built it. Their kit always feels like it was ment to br built and stay together but they also kept in mind that you will need to service it.

160102-IMG_20160102_140931The photo on the left shows one of four plastic “poppers” that hold the case halves together. There are also four bolts to hold the steel frame in but that’s it. Dead easy.

160102-IMG_20160102_141849

Check the power supply.

Using the diagrams in MP00633_VT100_Schematic_Feb82.pdf I checked the voltages on all of the pins. Everything is OK with the exception of the 12V line. I can see that there should be 12V on the orange wire but there is hardly anything there at all 0.4V and just ain’t enough.

Is that my problem?

Hmmm. The CRT uses the same 12V supply and you can see from the top photo that the CRT is working. When I tested the voltages I didn’t have the CPU board in and the CRT didn’t come on. When I plug the CPU board in, the 12V comes back.

Doh! Red herring.

 

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