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Model I - Things to check before applying power?

T

troj

Experienced Member
Joined
Apr 22, 2018
Messages
115
Location
Bellevue, NE
I just managed to arrange the acquisition of a Model I in unknown condition. It has an expansion and at least two floppy drives; I don't know what else is there. I'll know more when I pick it up (should be tomorrow).

I'm just a wee bit excited as the first computer I did any programming on was a Model I Level II back in about 1980.

Considering that it's unknown how long it's been since this unit has seen power, or what its condition is, I'm looking for pointers on what I should check before turning it on for the first time.

I'll be surprised if it doesn't need some love before it's fully working again.

-Kevin
 
troj said:
I just managed to arrange the acquisition of a Model I in unknown condition. It has an expansion and at least two floppy drives; I don't know what else is there. I'll know more when I pick it up (should be tomorrow).

I'm just a wee bit excited as the first computer I did any programming on was a Model I Level II back in about 1980.

Considering that it's unknown how long it's been since this unit has seen power, or what its condition is, I'm looking for pointers on what I should check before turning it on for the first time.

I'll be surprised if it doesn't need some love before it's fully working again.

-Kevin
Click to expand...

Model I's are pretty resilient. You can go ahead and plug it in and turn it on and see what happens. I suggest starting with just the keyboard unit and video display. Try the EI and drives after making sure the base system works as expected.

Let us know how you make out.
 
troj said:
I just managed to arrange the acquisition of a Model I in unknown condition. It has an expansion and at least two floppy drives; I don't know what else is there. I'll know more when I pick it up (should be tomorrow).

I'm just a wee bit excited as the first computer I did any programming on was a Model I Level II back in about 1980.

Considering that it's unknown how long it's been since this unit has seen power, or what its condition is, I'm looking for pointers on what I should check before turning it on for the first time.

I'll be surprised if it doesn't need some love before it's fully working again.

-Kevin
Click to expand...

Make sure you keep power in the power spot, nothing else connected, turn it on and see if you get a red light on the keyboard unit. Then turn on the monitor and see what happens. If you get a nice white/gray blank screen you probably have a good monitor. Turn it all off, connect video, try again. This will at least give you a known state for the monitor and CPU.

The EI, you need to be sure its got the right cable and its in the right direction. Does it have a BOX on the cable? Does it have a din thing hanging out the CPU and EI? Cleaning the card edges between CPU and EI is needed, use a soft pink eraser or something like DeOxit.

When you are good with all that, you power on the EI first, then the CPU. You should see garbage, hit reset and hold break and you should see Mem or Memory size.
Check ram with ? MEM. Should be 48k or 32k (Not exactly).

if you get this far, floppies will be next. Until they are cleaned and lubed, you shouldn't mess with them, because you could make things worse.

If you dont get what you expect at any stop, stop and assess. You could have a bad video ram, bad CPU, Bad cable, dirty contacts, and on and on. Even power levels might need adjusting, or bad video chain chips.

Model I is an experience. Others will chip in with great help this should at least give you something to assess.
 
I got my hands on the computer. Looks like I've got some work to do before powering it up. First and foremost, I don't have a monitor for it; I do have a composite monitor for my Apple //c, so I can build a cable to address that.

Since there are two power cords coming out of the Expansion Interface, I'm assuming the two power supplies have been stored away inside it. Not sure what condition those are in (yet).

First up is the Model I itself. I'm having a hard time finding information on the specific model number 26-01006-G. It needs some cleaning; with as dusty as it is, I'll likely pop the case open and blow it out, as I suspect there will be a lot of dust inside.

View attachment 46601View attachment 46602

Next up is the expansion interface. Based on the cables coming out of it as well as the model number, it appears to be a 32K expansion with a serial board.

View attachment 46603

Next up is the floppy drive. Nothing exciting here; this will need cleaning and lubrication before I try to do anything with it. I don't have any Model I floppies anyway, so no rush here.

View attachment 46604

These last two bits are something I've not seen before. The first looks to somehow be related to the use of a cassette player. The cassette plugs off of the expansion interface look to be connected to it, while the cassette plugs off of the Model I itself are not. The power cords from the two power supplies were plugged into this, so I suspect it also provided power switches for the computer itself. The other is what appears to be a stylus - it looks to be a modified ball point pen with a wire coming out of it. Attached to it is what appears to be a device to remove the need for a 9V battery. This was inside the box but not plugged into anything, and I have no idea what it is.

View attachment 46605View attachment 46606

-Kevin
 
I did a bit more cleaning/disassembly, in an effort to see what's there. I took pictures of all of the cable attachments before removing them, so I know where everything goes, as well as the proper orientation.

Opening up the expansion unit, I discovered what I think is an RS/232 board, but I'd like help in identifying it for sure. I'd also love to learn more about the DIP switch settings. Picture of the board follows:

trs80-7.jpg

I also verified that there are indeed two power supplies hidden away inside of the expansion interface. After disconnecting everything and wiping it down, I applied power to the Model I unit itself - I got a red LED, which is a good sign. It at least gets power! I'm waiting for components to build a composite video cable, so I'll know more this weekend.

-Kevin
 
troj said:
I did a bit more cleaning/disassembly, in an effort to see what's there. I took pictures of all of the cable attachments before removing them, so I know where everything goes, as well as the proper orientation.

Opening up the expansion unit, I discovered what I think is an RS/232 board, but I'd like help in identifying it for sure. I'd also love to learn more about the DIP switch settings. Picture of the board follows:

View attachment 46627

I also verified that there are indeed two power supplies hidden away inside of the expansion interface. After disconnecting everything and wiping it down, I applied power to the Model I unit itself - I got a red LED, which is a good sign. It at least gets power! I'm waiting for components to build a composite video cable, so I'll know more this weekend.

-Kevin
Click to expand...

That is the RS-232 board. The DIP switches are documented in the manual. I believe there's a copy on archive.org.
 
An update, now that I've received the parts of make a composite video cable - it works!

trs80-8.jpg

Don't judge me too harshly for using the monitor from my Apple //c -- it's the only monitor I have at the moment which accepts composite in. :)

I've only powered on the base unit, to verify that it works. My 14 year old son is now experimenting with it.

In the next few days, I'll test the Expansion Interface. I'll need to source a Model 1 floppy before I can test the floppy drive.

-Kevin
 
In the process of my youngest doing some work on the Model 1, we've discovered that the video goes unstable after a bit. It appears to be purely a horizontal stability issue and if we leave it unplugged overnight, it works for a few minutes the next day. Here's a short video of what it looks like:


In doing some poking about online, I'm guessing it's a problem with Z5 or Z6. I've found a video of a repair of a system with similar problems.

I've got a friend who's very handy with electronics who I'm going to have help me with the diagnosis and repair - while I can solder, he's much better at it than I am, and I'd rather not muck up the board. Once we know what the bad part(s) are, the ICs will get replaced with sockets and appropriate chips plugged into them.

His suggestion was, since it works for a little while, starting with a can of freeze spray since it's likely temperature-related.

Any input would be greatly appreciated.

-Kevin
 
That last image looks like a light pen.

I made one in the 80's for my BBC micro using a Honeywell sweet spot transistor.

Worked too !
 
Fixed a few Model I units myself with a can of freeze spray. I think your friend's suggestion is a good one. You can also just feel the devices and look for one that's warmer than the others, but freeze spray is better. Use static precautions.

You have verified that your monitor is OK?

Good luck with it!
 
You have verified that your monitor is OK?
Click to expand...

Fair question. I should probably test it, though I had the same results with two monitors, one of which we used recently with an Apple //c without difficulties.

-Kevin
 
Because shipping can be annoying, I want to order both freeze spray and possible replacement parts in one shot - the parts are cheap enough that I'm willing to spend $2 or $3 and order parts I may not need, in order to avoid an extra $10 shipping charge.

It appears I have a horizontal sync issue, so I want to order likely parts that will repair this. I'll also get a can of freeze spray so that we can test chips before randomly desoldering and replacing.

That said, I'm looking for input on confirming that I'm looking at replacements that will work.

Z5 is a 74C00N, so I think this is the correct replacement: https://www.digikey.com/product-detail/en/texas-instruments/SN74HC00N/296-1563-5-ND/277209

Z6 is a 74C04N, so I think this is the correct replacement: https://www.digikey.com/product-detail/en/texas-instruments/SN74HC04N/296-1566-5-ND/277212

Do this appear to be correct parts?

Thanks!

-Kevin
 
An update on this model 1 -It Lives!.

A friend and I spent a couple hours with cold spray and schematics, checking components, verifying voltages, etc. We figured out that whatever the culprit was had a very narrow temperature range where it was happy. With enough time spent working through things, we were fairly confident the culprit was Z5. Replacing that resulted in stable video - we left it on for about 20 minutes to verify. Prior to that, the longest the video would stay stable without starting to show symptoms was 5 minutes, and rarely that long.

The Expansion Interface doesn't work - I get a screen full of garbage when it's connected. However, I have not yet cleaned the edge connectors on either unit. Testing and diagnostics on that will have to wait for another day. My son is using my monitor to play games on my Apple //c at the moment....

-Kevin
 
troj said:
An update on this model 1 -It Lives!.


The Expansion Interface doesn't work - I get a screen full of garbage when it's connected. However, I have not yet cleaned the edge connectors on either unit. Testing and diagnostics on that will have to wait for another day. My son is using my monitor to play games on my Apple //c at the moment....

-Kevin
Click to expand...

Do you get the garbage when you hold down the break key while powering on? It could just be the normal garbage screen you get prior to the EI finding a boot floppy. Holding down the break key makes it boot into BASIC (as it does without the EI connected).


PJH
 
pjhacnau said:
Do you get the garbage when you hold down the break key while powering on? It could just be the normal garbage screen you get prior to the EI finding a boot floppy. Holding down the break key makes it boot into BASIC (as it does without the EI connected).
Click to expand...

Thanks - I'm new to the EI, so this is a learning experience in many ways. While the first computer I learned to program on was a Model 1, it didn't have an EI, so that's new.

If I hold down the break key when powering it on or resetting it, I get the memory prompt. Hitting enter and then typing "? MEM" I get 15572, which seems low.

-Kevin
 
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