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Micro Color Computer Dead (?)

As long as the voltage is correct, there is no problem using a DC power supply on a device that specifies a low-voltage AC power input. The DC will just pass through one half of the bridge rectifier. For example, my Magnavox Odyssey2 video game console specifies 9 volts AC, but it works perfectly with a Sega Genesis power supply providing 9 volts DC.

The difference between 8 and 9 volts isn't terribly important either, since the computer is just going to regulate it down to 5 volts anyway, and putting 9 volts into a device rated for 8 volts is only 12.5% higher, well within normal tolerance.
 
I've got the French licensed model, the Matra Alice and it takes 10VDC 1.3A but I realize it may have been reengineered since it also outputs RGB out, which the MC-10 doesn't.

However there is a note that the Matra Alice PSU should be good with the MC-10, and that the follow-up Alice 90 (only in France) can be powered with either power supply which might be a typo or misunderstanding.

The question was raised back in 2009, and Channelmaniac pointed out the MC-10 has a bridge rectifier and a 7805. If you run it on e.g. 9V DC you might have issues with serial communication, but otherwise it probably would boot.
http://www.vintage-computer.com/vcforum/showthread.php?17259-Trs-80-mc-10
 
vwestlife said:
As long as the voltage is correct, there is no problem using a DC power supply on a device that specifies a low-voltage AC power input. The DC will just pass through one half of the bridge rectifier. For example, my Magnavox Odyssey2 video game console specifies 9 volts AC, but it works perfectly with a Sega Genesis power supply providing 9 volts DC.
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Have you looked at the schematics for the MC-10? I have not, so I am being conservative in my suppositions.

You state that DC will just pass through 1/2 of the bridge--yes, with a diode drop. And who knows what that circuit is doing with the supply? Is there ANY transformer involved? If there is a backlight, and a transformer is involved, it's not gonna work well with a DC supply. The reactance will all be screwed up too. If there is a part of the input circuitry that figures into a reactance formula, and less is present because of the DC upfront, you could approach a virtual short.

Do we know for certain that the AC input voltage is over-spec'd just to provide 5VDC, and that nothing else but a bridge rectifier and a 7805 is involved?

I don't, without seeing the schematics. If you have taken one of these apart, or have the schematics, I stand corrected!

gwk
 
vwestlife said:
Here's the MC-10's service manual:

http://www.alice-dsl.net/d.j.peters/mc-10/ServiceManual.pdf
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Well it looks like, at most, the neg V for the comparator might be affected for the RS232 V swing. The only way to be 100% sure of any of this working at this point, though, is going to be to put a multimeter on the input/output of the 7805. We don't really know if the circuit is even alive & kicking...

PS Oh and you are right--since there is a Graetz bridge involved, it shouldn't really matter if the input is AC or DC for the supply to the 7805 (there will be difference in output voltage-slight-diode drops and all), and since the 7805 specs out @ ~35V for abs max input, even a 9V supply wouldn't make much of a difference, except to the LM339...

gwk
 
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To translate what you guys are saying into effect, what precisely would 8 V DC current do to the machine? Or not even precisely - is the interference I'm seeing in the screen actually evidence the machine does work?

That adapter is too expensive. Guy wants $13 from GA to NJ. That said, no clue where to find another.
 
My local Goodwill, Salvation Army, & 7th Day Adventist Thrift Store all have baskets full of power adapters in their electronic sections.

Mike
 
The thrift stores around me also have a lot of adapters. At this point I've looked through most of them. 8V AC seems to be a pretty weird standard. In any event, I made an offer on that one on eBay, so hopefully it works. Worst case scenario on the barrel, I'll just splice another one in.
 
The adapter came. The barrel doesn't fit.

When I splice another barrel connector on, the 8v AC plug has two distinct wires, one of which is labeled with a solid line interrupted by three dashes (then back to a solid line then three dashes etc etc etc). The barrel I'm putting on has red and black (neg) wires?

Look I'm not going to lie; I already tried it once and it did not work, although I saw similar flashes of light/interference on the screen. If someone can confirm the above suspicions (the dashed line is +?), I'll try more thoroughly and then I'll stop caring for another 15 years.

I'd never be able to recreate Gorillas anyway. (that's just a bad joke; not some original goal)
 
Okay, that explains the similarity of symptoms with each config. I guess it's either still an RF thing (waiting on the RCA to F adapter) or the thing really is dead, or there's a board problem. Tried it again after,; still no signs of life.

If I can't get it to work tomorrow I'll try to figure out how to take the keyboard connectors out. Even with the ... plastic 'clamps' unhooked the individual, pretty stiff, wires are wedged into the sockets somehow - or I'm overlooking something.
 
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raoulduke said:
8V AC seems to be a pretty weird standard.
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Although it is irrelevant to this discussion, at work we have some kind of telephone wiring running through all rooms. In each room there is a power adapter that outputs 8V AC 260 mA that supposedly goes with the wiring. It was installed some decades before I got here, and we've never used it so I can't tell how it works, but it is about the only other place that I've registered an use of 8V AC. Now they'd be all too weak to power a MC-10 anyway so irrelevant, as I mentioned.
 
Just to emphasize my addition to my previous post: I forgot to set up the RF initially, but having done that it still doesn't work. I also tried switching the cable box's RF channel to 4, then switching the physical RF adapter and the computer to Channel 3 but Channel 3 just showed up as static. I also removed the cable box and just went directly through the RF and that didn't yield a different result.
I'll wait for the adapter to come at this point and I'll solder the AC plug together in the interim in addition to just tape.

Anders, I think perhaps we can infer - because I found maybe 1 or 2 online also with a pretty weak amperage - that it's an obscure standard and, for the higher current ratings, one that hit its (still obscure) sweet-spot with random computer electronics in the early to mid 80s. The Microfazer II was I think an early print spooler; I'm not sure if that's accurate terminology - you sent the print job to the Microfazer and it progressively sent it to the printer, freeing the computer to do stuff in the interim. But so those are the confirmed +1.5A uses - the Microfazer II and the MC-10...
 
carlsson said:
Although it is irrelevant to this discussion, at work we have some kind of telephone wiring running through all rooms. In each room there is a power adapter that outputs 8V AC 260 mA that supposedly goes with the wiring. It was installed some decades before I got here, and we've never used it so I can't tell how it works, but it is about the only other place that I've registered an use of 8V AC. Now they'd be all too weak to power a MC-10 anyway so irrelevant, as I mentioned.
Click to expand...

If this is distributed power, it makes sense that they used AC - Just remember the Edison vs Westinghouse debate (War of the Currents) when AC won because of line loss in DC.

Whatever the AC was used for, if it was running over the phone line cable, it's just good engineering to use AC for that kind of thing. It can always be rectified at the destination...

gwk
 
raoulduke said:
Then I got an RF modulator and noticed minor interference on the TV (when I flipped the switch), but no obvious response from either the computer (I don't know if it's supposed to do anything) and no actual picture on the TV.
Click to expand...

This is probably stupid ??s to ask, but first, what kind of a TV are you using--hopefully this isn't a new one, with digital-only tuner???
Also, have you tried any other input to the TV, from a different source, that works?

Just to be thorough...

gwk
 
It's a TV that's been in the basement since the late 90s. It is not at all digital.

What do you mean by other inputs? The cable works. The Wii works. I could try plugging it directly into the RCA video input (Input 1) on the TV itself but I probably did last night also.

And you're sure it won't work just directly into the Apple RGB Monitor I used with my Commodores and use with my //e?
 
No you're probably right. It doesn't work plugged directly into Video 2 either, but I'm sure I've tried that before. The TV is a Toshiba CF36H50. I mean I suppose it's possible the adapter doesn't work.

Or actually maybe the fact that it works on neither isn't attributable to the screens - (http://www.classiccmp.org/cini/pdf/Apple/Apple RGB Monitor.pdf) the RGB appears to support both PAL and NTSC. I suspect that's why I specifically kept that monitor when I threw most of my collection out 15 years ago.
 
Like we've already said, the MC-10 has a channel 3/4 RF output, so it will never work with a composite video input, even if the plug fits. :p
 
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