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ADM-3A repair options?

B

bucka

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Joined
Nov 26, 2023
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7
Hi, I picked up a non-working ADM-3A from eBay. It came with a surprise RG-512 Retro-Graphics card installed. I was planning on working through the repair myself but the RG-512 Retro-Graphics card is rare. I don't want to risk damaging it and I'd love to show it in action online and at a VCF.

I'd like to find some help:

- Good: Someone capable who I can afford (including Raleigh, NC USA shipping)
- Better: Someone local enough that I don't have to risk shipping
- Best: Still doing some or all myself, with (paid) guidance

About this ADM-3A

- Video card dislodged when I received it.
- Power on beeps and displays a dot that scrolls off the screen.
- Typing bell character emits beep.
- Nothing looks wrong to my (untrained) eye.
- Power rail checks look good (to a novice).

Any advice?
 
Jerry Walker did a series of YouTube videos on the restoration of an ADM-3A including rewinding the transformer. Not sure if that helps much but it might give you an insight into what sort of things you might encounter.
 
Those were excellent! I watched them all, repeating sections I worked on like checking power rails. I'd prefer a "boost" to get this thing up and running but Jerry's videos are an excellent fallback plan.
 
Did you make an progress on this? I have an ADM-3A that worked great until it recently stopped sending keystrokes. I plan to rewatch the Jerry Walker videos to see where I need to start.
 
Does your board have socketed ics or are they all soldered in place like mine? Could you please share photos of the graphics board you are mentioning?
 
Hi bucka,

I also have an ADM-3A with bonus RG-512. So, courage! There are at least two of us.

Anyway, the RG-512 inserts itself into the serial and video signals and can become a wellspring of chaos and despair if it's malfunctioning, so my advice is to unplug and remove the card first and try to get the terminal working without it. You will need the original UART or a replacement AY-5-1013A (look on eBay) to go into the socket where the RG-512 ribbon cable connects.

Once the terminal is working on its own you can tackle the graphics card. So maybe give this a try and see what happens?

- rob
 
I get the feeling the OP joined and isnt coming back. Apparently 24 hours was more than enough time to have a plan on fixing the ADM3A. I guess we failed him.
 
ajacocks said:
I had never heard of the RG-512 until now. Is there a good video out there showing one in use?
Click to expand...

Hi,

I had never heard of it either, until I opened up my terminal and there it was. The basic idea is that the RG-512 intercepts serial IO and interprets Tex 4010 escapes, so you can use it with existing software that was written for Tek storage tube terminals. That's the main use case as far as I can tell. It does this by mapping the 1024x780 logical canvas onto a 512x250 physical pixel grid, so the fidelity is pretty crappy but it's still fun.

On the output side the card intercepts the video signals coming from the main board and mixes its pixel data into the scan lines. So the two signals are independent and text scrolls underneath static graphics, which is a cool effect.

Anyway, I couldn't find any videos at the time, but I have a repair thread on Mastodon here that has bunch of photos and a few short video clips. I can make a longer one at some point, but the aforementioned video mixer started dying yesterday so it's back on the bench at the moment.

Thanks for your interest! I really love this stuff.

- rob
 
Sorry guys, I missed that you were responding!

@toby405 No progress. I occasionally search for a local repair shop that could do this sort of work but no luck so far. I have a goal of traveling to a repair workshop to get the courage to use the soldering iron on it :).

@VERAULT socketed: https://photos.app.goo.gl/cMZ8XBeEbT89yvLM6

@tpolecat I'll try that next - any reason not to re-home the UART from the RG-512 back to the ADM-3A board? Thanks for the tip!

@ajacocks I found an old demo video showing a few plots but I can't seem to find it now. I'll post if I see it again.

I was surprised not to see a modern demo and then surprised again to see yours, @tpolecat. Thanks!
 
Please be aware that the RG512 option requires an updated, beefier transformator : the original ADM3A transformer is insufficient. That transformator was part of the upgrade kit back in the day.
I also have a RG512 equipped ADM3A, but never used it as I also have the real thing : the Tektronix 4014, fully functional....
 
bucka said:
@tpolecat I'll try that next - any reason not to re-home the UART from the RG-512 back to the ADM-3A board? Thanks for the tip!
Click to expand...

I had a quick look at the data sheets and everything has different names (intentionally, I assume) but the pin functions appear to be the same. You should have a closer look probably, but yeah it seems like maybe a swap would work.
 
jdreesen said:
Please be aware that the RG512 option requires an updated, beefier transformator : the original ADM3A transformer is insufficient. That transformator was part of the upgrade kit back in the day.
Click to expand...
I have the original transformer but it looks like there's a power supply on the RG-512 and an AC connection to supply it. Could there be different versions with different power configurations? Mine aligns with this version of the UG: https://vt100.net/lsi/rg512-um.pdf
 
tpolecat said:
I had a quick look at the data sheets and everything has different names (intentionally, I assume) but the pin functions appear to be the same. You should have a closer look probably, but yeah it seems like maybe a swap would work.
Click to expand...
I also noticed that the UART you mentioned, AY-5-1013A, isn't what I have on my RG-512 (AY-3-1015D). Definitely looking closer, thanks!
 
The IC puller I ordered came in the mail today and I move the UART over to the ADM-3A board. Here's an update:
Power-on gets a beep, Ctrl-G gets a beep, nothing on the display, power-off draws a vertical line down the middle of the CRT.
I think my next move is to probe with an oscilloscope to look for screen data. Just need to learn how to use it and where to probe. Breaking out the manuals.
 
The 1013/1013A needs -12 volts on pin 2, otherwise it is pin-compatible with the 1014A and 1015D. There is also a CDP6402 which is pin-compatible with the 1015 (I think my own ADM-3A has a 6402). The ADM-3A schematic indicates that it provides -12 volts for pin 2.

A data sheet I have says that the 1014A is CMOS compatible, and can operate from +5 to +14 volts. Also, the 1014/1015 when set to 5 bits per character and 2 stop bits will produce 1 1/2 stop bits.
 
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