Interact Home Computer restoration / exhibit

[mrthreeplates]

I've finally started to restore my Interact Home Computer. For those not aware of these unusual home computers, they only sold a few thousand. Many bought them (like a friend of mine when I was a teen), via mail order from Protecto Enterprizes (sic). See:

Interact Home Computer - Wikipedia

en.wikipedia.org

Protecto Enterprizes: What is was and wasn't

Protecto Enterprizes was a large phone/mail order distributor of computers based out of Chicago from 1979 to about 1995. This is its story.

dfarq.homeip.net

These computers were affordable, especially for the time, but had quite a few quirks. My friend and I spent many an afternoon trying to develop software, so it has a special place in my heart.

Anyway, I was lucky enough to score a complete Interact Home Computer on Ebay a few years back. It included 15 tapes, and a very nice collection of documentation. The diagnostic and alignment tapes might be of particular interest as my unit isn't working... yet (I hope). It has been collecting dust for a while, so this is going to be a project.

If any of the documentation or tapes aren't available, I'd be happy to upload them for others.

I hope to get this working in time for VCF West, to be exhibited.

Some quick pictures before I tear into it. Yes, the keyboard was horrible, but so were many of the "affordable" computers at the time. To a kid, this wasn't so important.



Sadly, the warranty seal is broken... Typical eBay! I guess I'm on my own!



From what I can tell, "Football", "Craps", "8080 Monitor", and "Alignment" might be titles not yet in the archives...

There are quite a few manuals in the bundle, so I am hoping there are some things new here:

16K RAM Personal Computer Service Manual
Users Manual
16K RAM Personal Computer Schematics and Parts List
8080A Machine Language Monitor Program (Manual)
Model one diagnostics tape instructions
Interact Family Computer Owner's guide
StarTrack Program Guide
Basic Programming Examples Book 16k ram
Interact Electronics level II basic language reference cards (2 pages)
Warranty instructions (this is fun to read...)
Plus a few other bits (original receipt, price list from Protecto, etc).



Sadly, the typical "Press L to Load" screen does not show up upon powerup or reset. Pressing any of the keys doesn't do anything.

Oh darn, I will have to take it apart... I'm guessing bad ram, but we'll soon find out! What's your guess?

 

[mrthreeplates]

So, took it apart for an initial exploration:

Keyboard, cassette are bolted to the top, there is a clam shelled PCB on the bottom.



Unfortunately, not many chips are socketed (except the DRAM, ROM and 8080A).



As I don't have an 8080A tester, I started pulling the RAM chips (8x 4116) in hopes one was bad. Two were immediately suspect as they appeared to be older TIs, and had really crusty legs. The remaining 6 were NEC. As I have a few DRAM testers, I checked all of the chips. The second TI chip failed completely, wouldn't even pass the pre-power on test of the tester. Even though only one was bad, I swapped out both TI chips for good measure. I also added some Deoxit, and powered it back up:



Success! Well, sort of... The screen is *REALLY* noisy, but it is clearly working. I plugged in the keyboard, and got the tape motor to start when I pressed 'L'. So, a lot is working now. I'm quite pleased!

I imagine what happened is that some time it its history, the RAM had failed and 6 of the chips had been replaced with the newer NECs. Later, the remaining TI chip failed, and it was tossed in a corner until sold to me.

Of course, the cassette belt is toast, as the spindles barely turn. However, that doesn't bother me as I will be using a bluetooth cassette adapter.

But before I try to load some software, I really need to fix the crappy display.

I dug into the RF modulator a bit:



However, the only adjustment seems to be that coil on the left. There is a hole in the top cover of the computer, so it is meant to be adjusted while the computer is assembled. However, adjusting the coil didn't seem to make any difference in the picture quality.

I have full schematics, which helps a ton.

Any suggestions on what to try next to fix the video? I'm assuming something is wrong with the RF modulation, but I'm not sure what.

I did find this thread on a successful S-video mod, perhaps I'll try that. However, I'd like to fix the RF if I can. The picture doesn't have to be perfect as it is super low resolution anyway.

https://forums.atariage.com/topic/266348-interact-home-computer-repair/

Thanks,

 

[mrthreeplates]

FYI Here's a fun ad from popular science (Nov 1980) advertising the interact computer.

 

[snuci]

I'm not so sure it looks that bad. You might want to connect it to a TV, if possible. I have an LCD with antenna input and it's hit or miss to get any signal at all. For the record, it doesn't look stellar to begin with and I have a later version.

 

[mrthreeplates]

Hi snuci,

Thanks, that is a nice looking interact! I love the government sticker! I see they fixed the keyboard and the annoying placement of the 1 key.

I also noticed some of that hit or miss behavior on my interact. If I unplug the rf output and reconnect it, my lcd tv won't retune the signal. If I either change channels on the TV or power cycle my interact, the TV will relock the signal. So something must be mismatched between the interact and my lcd tv. I wonder what the incompatibility could be in the signal? I may try to look at the rf output on my scope to see if I can spot anything.

I also get a bad picture on the rf output of my imagination machine, though it seems better. Perhaps a common issue?

I'll have to hunt around for a true analog TV, I don't have one at the moment.

Much appreciated,