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Model 12 schematics, service manual

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kyeakel

Experienced Member
Joined
Jul 27, 2009
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491
Location
Curwensville, PA
I just got a model 12 that has the MF boot error. I see from the manual it's a memory error. Does anyone have the schematics and board layout diagrams for this computer? I downloaded all the manuals I found online and searched for SAMs computer facts to no avail. I did find the model 2 troubleshooting guide and schematics, and I know the model 12 is the follow-on of the model 2. Are the model 2's documents the same?
Thanks for any help,
Kipp
 
kyeakel said:
I just got a model 12 that has the MF boot error. I see from the manual it's a memory error. Does anyone have the schematics and board layout diagrams for this computer? I downloaded all the manuals I found online and searched for SAMs computer facts to no avail. I did find the model 2 troubleshooting guide and schematics, and I know the model 12 is the follow-on of the model 2. Are the model 2's documents the same?
Thanks for any help,
Kipp
Click to expand...
Check this link:
http://www.oldskool.org/guides/tvdog/documents.html

Also, the Model 12 is the upgraded version of the Model II. Your floppy is different and the mobo is a single board. However, software-wise, it is fully compatible with the Model II and is even capable of running Unix. Nice find - lets us know how you make out.
 
AgentOrange,
Thanks for the link, I only see Tandy 1000 and newer stuff here, though. Perhaps you had a different link?
Kipp
 
If I remember correctly the Model 12 I thought was the 68000 series unless it could be either still (CPU board). That may make a difference but I'm not sure. The model 16 could do either processor and I think the 6000 was a 16 with a built-in hard drive.

Looks like the Owner's manual is supposed to have some schematics if you can find it. Model 12 Owners Manual may have it? (It's not loading here but we have a lot of web filtering/blocking crap on our network).
 
The 12 was a 16b without the card cage and just the video card installed. No 68000 CPU installed. However, the 68000 CPU was an option if you added a card cage and bigger power supply.

If boot error MF is a memory error, the memory has to be either on the main board or the video board. The memory is very easy to identify. I have the model 6000 service manual and schematics, but I have never scanned them.
 
The first thing to try is, when you get the Boot Error MF, hit the reset button and see if it then goes to the first floppy and gives you a Boot Error D0. If it does, it's a tiny mod to the motherboard to set the memory to a known state on power up.

If you get Boot Error MF again, then you'll have to remove the video card and all the motherboard shielding (PITA) and swap out the 64K x 1 chips until it stops doing it on power up and that's your bad RAM.

If it reacts as in the first paragraph, you can save yourself a lot of hassle by just hitting the reset when you get the Boot Error MF
 
I did try the reset trick, I get MF every time. The chips that are installed are ones I am not familiar with. What should they be? 4164's?
 
kyeakel said:
I did try the reset trick, I get MF every time. The chips that are installed are ones I am not familiar with. What should they be? 4164's?
Click to expand...

Yes, there will be a - and a number after the part number (it won't be a 4164, it will be a Tandy part number, but they are 4164s or equivalent), that's the speed you want to get, but, ISTR they were 200mS chips, but don't quote me on it as I'm not about to go downstairs and tear a Model 12 apart to make sure.

As luck would have it, they are in sockets.
 
Well, I replaced the tandy part number chips with 4164s, no change. So I replaced the 4116s as well, still no change. I started to debug with a z80 ice, started walking thru the rom boot up which seems to start in high memory and write 0xA0 to each memory location from top down. Got a ways into this when C2 in the power supply burst open and started smoking. I quickly shut her off. Any idea what would be a good replacement cap for this? I think it was a 0.22uf 250v, I should probably replace C1 as well (same type but 0.1uf) the electrolytics look good, no bulging. I don't suppose anyone has a dump of the model 12 boot rom? The one in my machine has no lable covering the window, I'm concerned that maybe it's corrupted.
I'd still like a copy of the service manual for this, I found service manual for model 2 on the web, and schematics for the model 16, but nothing but the owners manual on the model 12.
Kipp
 
Isn't the model 12 just the model 16 without the 68K CPU cards? The schematic for the 16 should work for the 12 in that case.

Also, if the 16's ROM would be useful, I could dump that for you.
 
Well I replaced the C2 cap with a similar one 0.22uf 180v Mylar. Thought is that I won't need the 240v capacity of the original since the computer will always be used in 110V mode. Checked all the voltages, and then reconnected the supply. I'm now back where I was. I removed the 2716 uveprom and dumped the contents. Reading the model 2 service manual has a description of the boot steps, the A0 I was seeing before is used to paint the screen white. I've got the rom in intel hex, binary, and disassembled into an assembly language listing. If I knew the memory&I/O map for the machine, figuring this out would be easier.
Kipp
 
Continued tracing with a Z80 ICE and digital logic probe. The 4116's have a RAS but no CAS, the 4164's don't have RAS or CAS. Neither of the model 2's or 16's schematics seem to match the model 12. I will probably have to remove the motherboard and trace these signals by hand. I have decoded alot of the ROM in the machine, so if anyone needs that let me know.
Kipp
 
Just remember to pay attention to the particular version of any PCB(s) mentioned in the Tech Tips as I had a junior technician once go wildly trying to apply them to boards that either didn't need them or already had them.
 
Does anyone with model 16 schematics have ones that show U81 as being an S112? My board has the mod that Druid mentioned, so my next step is going to be to remove the main board and trace the RAS and CAS circuit by hand.
Thanks for the suggestions,
Kipp
 
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