Normally there is an RF shield covering the front of the board. Most of these machines had the ROM soldered in, so the lower socket was probably added. The upper ROM socket is an adapter for the different pinout of the EPROM. The wires to the SRAM chips are the additional address line from the 6847, and chip select lines. The additional 4K lets you use hi-res graphics. Your other wires / piggybacked chips are for the additional address decoding logic to use the new RAM. There's normally 1 piggy backed chip fixing a problem from the factory. Other chips on the board are: A latch for demultiplexing some pins out of the CPU to get the full 16 bit address Chips used to control output to and input from the keyboard. A latch to hold the settings for the VDG (The 6847T1 would not require this, as it's internal) Some chips for address decoding Chips (chip?) to divide the clock signal to generate the proper frequency. The 6803 and VDG get alternate signals so they can share the buss on alternate clock cycles.
Ahoy, the 4K RAM upgrade I did in 1984 (thanks Green Mountain Micro) added Graphics RAM so you could do hires without destroying the BASIC program space. Microsoft had the Graphics RAM butt right into the BASIC scratchpad and program area. Poke into the hires mode and run a basic program and you can watch the RAM changing as it runs on an umodified MC10. With the mod you poked down into the lower 4K and changed the location of start of VRAM and voila! HiRes on the MC10. daveyb aka MC10GURU
Your comment on the MC10 emulator got insta-blocked by TH-cam since it had a link in it, apparently you can only post links if you are a sketchy porn spammer! I did read it so a second like for that one!
Thank you, subscribed to your channel, my neighbor had one of these and those were the only times i got to interact with computer till I was a teenager.
I have a small stack of MC10. I built a cassette cable from the schematic and discovered that the motor control or remote was shorted on the computer connector. It appears to be the same cable for the Coco II but the II doesn't short the remote
I don't believe the MC10 uses the motor control so the remote cable doesn't need to be plugged in. It is the same cable across a number of Tandy computers (MC10, all 3 CoCo's, the model 100...)
Be sure to check with Ed before purchasing things on the zipster store, not everything is available. I think, considering the likelihood of undoing the Frankenstein modification would be pretty difficult unless you're an expert with hardware and the MC-10, and your desire to keep this anomaly as is, that's a good idea. Also, you could pick up a normal unit pretty cheap, and use the expansion pack with that. Thing is, who would go through all that trouble just to add 4k when one could easily add 16k by adding an expansion pack? Seems like whoever created the modification didn't think it through very well, because a proper mod would have allowed the expansion pack to be added plus the internal 8k. Anyways, thanks for the peek inside.
I really enjoyed looking at the guts of this machine! As for picking up another MC10, in my collecting I try not to just go on e-bay or things like that and buy them. For me the fun is going to second had shops, estate auctions and such to find things, so it may be a while before I come across another but I am definitely keeping my eyes open!
Just so you are aware (if you are not already), there is some RAM, etc. upgrades that don't cause problems that are commercially available. Scroll to the bottom of the following page to see 4 hardware upgrades for the MC-10 (MCX-128 in particular works very well, and adds a lot of functionality-128K RAM, Extended BASIC, and even loading programs from a PC): thezippsterzone.com/hardware/
Cool find! I think the mod is from the 1980''s. The chips all seem to be from about 1983. Since the MC10 is pretty easy to find on the net. BTW I have the MCX-128 upgrade, love it.
When I get my hands on another MC10 I want to look into something like the MCX-128. I am keeping this machine as is so any memory expansion that plugs into the edge connector will run into the same interference problem.
I've just put my PAL (i.e. Australian) MC10 on the bench to see if it still works. Interesting little machines. By the way what on earth is your ESD strap connected to?
@@CanadianRetroThings Hey, I suspected that. Honestly not trolling but that really achieves nothing. Attaching the ESD strap to ground will just ensure that YOU are at the same potential as ground. It does nothing to protect the equipment you are working on. The key issue is that you need to reduce the potential difference between YOU and the equipment you are working on. At the moment the MC10 (for example) may have built up a static charge of thousands of volts relative to you(and ground), touching it will still cause an ESD event. In the absence of a dissipative ESD work mat you would be better off connecting the strap to the ground of the MC10. This eliminates the potential difference between you and it - the rubber mat etc are still potential issues. In a lab environment we do reference things to ground but only as a common point. So the floor is static dissipative and grounded, the bench mats are grounded and our wrist straps are grounded. It's not the act of grounding that is protecting our stuff from ESD events but the fact that everything possible is at the same potential. In your case I'd recommend you use an ESD mat with the strap attached to it and that can optionally be grounded. Remember that walking around with a bare PCB or static sensitive parts can still lead to an ESD event when you put it on a shelf etc. ESD is very widely misunderstood, even in professional environments so don't feel bad. Cheers.
@@ingmarm8858 I do agree that a static mat would be more ideal, as it is I am only using the wrist strap to discharge any static charge from my own body.
@@CanadianRetroThings I think you are missing the point that this does NOT protect what you are working on as the potential difference i.e. static charge STILL exists between you and the item you are working on regardless of your grounding!
Wow, did you get a lot of this wrong. The 74LS32 is a quad OR gate, not an inverter. The 74LS125 and 74LS139 are mounted on 74LS367 and they are NOT the same kinds of chip. The 74LS32 is a factory bodge and not a part of the modifications.
I will be the first to admit that I am only just learning about how these chips work but the inverter chip (74LS14) is the chip I was talking about at U12, which is the chip listed in the service manual. As I couldn't see the bottom chip that the wire was attached to, I made the assumption it was the original chip listed in the parts list.
Tandy made a mistake when they still made computers, the original TRS-80 was a Z80 machine but the "color" computer was not a Z80 machine but it had a 6809 microprocessor. Therefore there was a division and programmes of one could not be used by the other. Why did Tandy do this! No question-mark, because there is no-one to answer any more. The Z80 is still being produced and used while the 6809 is a curiosity, derailed to a remote side track of history.
The 6809 was not used in the MC 10, it was the cost reduced 6803. The 6809 has an improved version, the 6309, which is a drop in replacement that is still used and made currently. Places like Retro Rewind still sell them, new stock, so I would disagree that they are a remote side track of history.
What a total rat's nest of a mess inside, why did somebody even bother for 4K extra, no programs would ever need that. The MC-10 reminds me of the Oric 1 sold in the UK and Europe.
Kudos for not removing the upgrade. It is unique. The upgrade is exactly the same as the one I did on my MC-10 recently.
Someone put some real work into doing this upgrade so I can't in good conscience mess with it.
Normally there is an RF shield covering the front of the board.
Most of these machines had the ROM soldered in, so the lower socket was probably added.
The upper ROM socket is an adapter for the different pinout of the EPROM.
The wires to the SRAM chips are the additional address line from the 6847, and chip select lines.
The additional 4K lets you use hi-res graphics.
Your other wires / piggybacked chips are for the additional address decoding logic to use the new RAM. There's normally 1 piggy backed chip fixing a problem from the factory.
Other chips on the board are:
A latch for demultiplexing some pins out of the CPU to get the full 16 bit address
Chips used to control output to and input from the keyboard.
A latch to hold the settings for the VDG (The 6847T1 would not require this, as it's internal)
Some chips for address decoding
Chips (chip?) to divide the clock signal to generate the proper frequency. The 6803 and VDG get alternate signals so they can share the buss on alternate clock cycles.
Ahoy, the 4K RAM upgrade I did in 1984 (thanks Green Mountain Micro) added Graphics RAM so you could do hires without destroying the BASIC program space. Microsoft had the Graphics RAM butt right into the BASIC scratchpad and program area. Poke into the hires mode and run a basic program and you can watch the RAM changing as it runs on an umodified MC10. With the mod you poked down into the lower 4K and changed the location of start of VRAM and voila! HiRes on the MC10.
daveyb aka MC10GURU
Your comment on the MC10 emulator got insta-blocked by TH-cam since it had a link in it, apparently you can only post links if you are a sketchy porn spammer! I did read it so a second like for that one!
Thank you, subscribed to your channel, my neighbor had one of these and those were the only times i got to interact with computer till I was a teenager.
The MC-10 has a lot of people making games as well as hardware for it now. It is an impressive little machine!
@@CanadianRetroThings I may revisit it in the future, doing more things with the raspberry pi and Arduino platform these days though
I have a small stack of MC10. I built a cassette cable from the schematic and discovered that the motor control or remote was shorted on the computer connector. It appears to be the same cable for the Coco II but the II doesn't short the remote
I don't believe the MC10 uses the motor control so the remote cable doesn't need to be plugged in. It is the same cable across a number of Tandy computers (MC10, all 3 CoCo's, the model 100...)
@@CanadianRetroThings that's good to know, I will build three more cables, thanks
Be sure to check with Ed before purchasing things on the zipster store, not everything is available. I think, considering the likelihood of undoing the Frankenstein modification would be pretty difficult unless you're an expert with hardware and the MC-10, and your desire to keep this anomaly as is, that's a good idea. Also, you could pick up a normal unit pretty cheap, and use the expansion pack with that. Thing is, who would go through all that trouble just to add 4k when one could easily add 16k by adding an expansion pack? Seems like whoever created the modification didn't think it through very well, because a proper mod would have allowed the expansion pack to be added plus the internal 8k. Anyways, thanks for the peek inside.
I really enjoyed looking at the guts of this machine! As for picking up another MC10, in my collecting I try not to just go on e-bay or things like that and buy them. For me the fun is going to second had shops, estate auctions and such to find things, so it may be a while before I come across another but I am definitely keeping my eyes open!
Just so you are aware (if you are not already), there is some RAM, etc. upgrades that don't cause problems that are commercially available. Scroll to the bottom of the following page to see 4 hardware upgrades for the MC-10 (MCX-128 in particular works very well, and adds a lot of functionality-128K RAM, Extended BASIC, and even loading programs from a PC): thezippsterzone.com/hardware/
Thanks, I'll check them out.
@@CanadianRetroThings Be aware, *none* of the upgrades work with the internal upgrade. In order to use them you will need a stock MC-10.
@@Gerardus1970 Another stock MC-10 is now on my shopping list!
I have cats so I subscribed. Big grey one you gave there.
Cool find! I think the mod is from the 1980''s. The chips all seem to be from about 1983. Since the MC10 is pretty easy to find on the net. BTW I have the MCX-128 upgrade, love it.
When I get my hands on another MC10 I want to look into something like the MCX-128. I am keeping this machine as is so any memory expansion that plugs into the edge connector will run into the same interference problem.
I've just put my PAL (i.e. Australian) MC10 on the bench to see if it still works. Interesting little machines. By the way what on earth is your ESD strap connected to?
I have it attached to a grounded power outlet box, not the power outlet itself, just the box.
@@CanadianRetroThings Hey, I suspected that. Honestly not trolling but that really achieves nothing.
Attaching the ESD strap to ground will just ensure that YOU are at the same potential as ground. It does nothing to protect the equipment you are working on.
The key issue is that you need to reduce the potential difference between YOU and the equipment you are working on. At the moment the MC10 (for example) may have built up a static charge of thousands of volts relative to you(and ground), touching it will still cause an ESD event.
In the absence of a dissipative ESD work mat you would be better off connecting the strap to the ground of the MC10. This eliminates the potential difference between you and it - the rubber mat etc are still potential issues.
In a lab environment we do reference things to ground but only as a common point. So the floor is static dissipative and grounded, the bench mats are grounded and our wrist straps are grounded. It's not the act of grounding that is protecting our stuff from ESD events but the fact that everything possible is at the same potential.
In your case I'd recommend you use an ESD mat with the strap attached to it and that can optionally be grounded. Remember that walking around with a bare PCB or static sensitive parts can still lead to an ESD event when you put it on a shelf etc.
ESD is very widely misunderstood, even in professional environments so don't feel bad. Cheers.
@@ingmarm8858 I do agree that a static mat would be more ideal, as it is I am only using the wrist strap to discharge any static charge from my own body.
@@CanadianRetroThings I think you are missing the point that this does NOT protect what you are working on as the potential difference i.e. static charge STILL exists between you and the item you are working on regardless of your grounding!
Thanks for the information, I now have an ESD mat on order!
Wow, did you get a lot of this wrong. The 74LS32 is a quad OR gate, not an inverter. The 74LS125 and 74LS139 are mounted on 74LS367 and they are NOT the same kinds of chip. The 74LS32 is a factory bodge and not a part of the modifications.
I will be the first to admit that I am only just learning about how these chips work but the inverter chip (74LS14) is the chip I was talking about at U12, which is the chip listed in the service manual. As I couldn't see the bottom chip that the wire was attached to, I made the assumption it was the original chip listed in the parts list.
Tandy made a mistake when they still made computers, the original TRS-80 was a Z80 machine but the "color" computer was not a Z80 machine but it had a 6809 microprocessor. Therefore there was a division and programmes of one could not be used by the other.
Why did Tandy do this! No question-mark, because there is no-one to answer any more. The Z80 is still being produced and used while the 6809 is a curiosity, derailed to a remote side track of history.
The 6809 was not used in the MC 10, it was the cost reduced 6803. The 6809 has an improved version, the 6309, which is a drop in replacement that is still used and made currently. Places like Retro Rewind still sell them, new stock, so I would disagree that they are a remote side track of history.
What a total rat's nest of a mess inside, why did somebody even bother for 4K extra, no programs would ever need that.
The MC-10 reminds me of the Oric 1 sold in the UK and Europe.
The homebrew scene for this computer has released a lot of good little games as well a some really powerful add ons for it.