Source for Model I parts?

[mlaferriere]

Hello Folks.

I have two Model I's. One is the one I had when I was a kid. Me and my late father used the heck out of it. We had a copy of one of the modifications for the Model-I so we added lower case and the 2.5MHZ hack. I would really like to get this going again for sentimental reasons. The original Model-I I had came with the flat keys and the keybounce problem. It was an early machine. We traded it to another member of the Western Massachusetts Computer Club for a newer Model-I and threw in one of those 35 track drives to make it worth his while. So its one of the later ones that had the unbuffered EI cable. We lucked out as he bought an EI one Christmas and the salesperson didn't know much about the EI's so when they plugged it in and did the ?MEM it came back as 16K (it was never turned on at the store and instead came with 32K installed...). Jackpot!

A few years ago I bought a full model-I setup (with boxes and the TRS-80 table!) for $50! I never powered it on but looking at the EI power supply, it got really hot and even has some charring on the inside. The people who sold this Model I named it "Clyde" for some reason. Its a buffered setup.

Now, I can't find my original EI power supply. The original KB power supply smoked up on us decades ago and my father (ex USN, tech instructor at the former Technical Careers Institute, Component Level Repair at MassMutual) made a replacement using two transformers and four power diodes to make a full wave rectifier.

My problem is, I have two Model-I's with maybe one (at this point) power supply. What is the power consumption for the Model-I and EI? I was thinking of doubling up the power diodes in the rectifier or just replacing them with a rectifier and just using the cord from the blown power supply. I will also need to find a non-buffered EI to KB cable if the buffered ones arent compatible.

Please help as I really want to see the original Model-I me and my father had and I also want to play "Temple of Apshai" again!

 

[mlaferriere]

in a nutshell (instead of a long message), two things I need to get started. Model-I power supplies. Are the expansion interface and keyboard power supplies the same? What are the requirements for the keyboard to EI cable? Would a straight through 40 pin cable be all that is needed with an unbuffered EI?

 

[Dustym]

Contact Ian Mavric (Mav) for details of his 'modern' power supply. Keyboard & E/I supplies use the same type of Tandy power brick. I think getting rid of the buffered cable might be a bit more tricky. Again, have a work with Mav.

 

[pjhacnau]

Contact Ian Mavric (Mav) for details of his 'modern' power supply. Keyboard & E/I supplies use the same type of Tandy power brick. I think getting rid of the buffered cable might be a bit more tricky. Again, have a work with Mav.

Providing a bit more info . . . Mav is on the forum as TRS-Ian, and his site is ianmav.customer.netspace.net.au/trs80/

 

[Chromedome45]

The un-buffered EI cable is a straight through 40 pin to 40 pin cable. Keep length short around 6 inches.

Power supplies occasionally show up on eBay. So check there. It is possible to make a power supply using 2 transformers. a bridge rectifier and a 1000uF capacitor 25 volts or greater. I built one a while back using these parts and 2 12.6 V 1.2 Amps transformers I got from Radio shack a couple of years ago. Both the model 1 and EI use same power supply.

Here is the schematic I used. http://www.trs-80.com/wordpress/zaps-patches-pokes-tips/zaps-model-i-power-supply/ Hope this helps.

Also this is what it looked like.

 

[mlaferriere]

Are those two 1.2A transformers in the picture? Judging by the minimum requirements on your notes, would there be any downsides supplying the keyboard and EI simultaneously from the same supply?

I think I am going to build up your basic everyday linear power supply such as in your schematic and modeling the one my father made some years ago. Unfortunately, Radio Shack doesn't carry the good stuff anymore. Are the RS 5 pin dins the same as a midi cable? I ordered a 15' Monoprice MIDI cable on Amazon. I plan to cut it in third and just use the ends.

The replacement transformer my father made used a 3A and a 2A transformer. The center taps of the 3A fed the AC at pins 1 & 3. The smaller 2A transformer was fed into a full wave rectifier for the DC at pins

 

[Audronic]

@mlaferriere

The midi Cables probably won't handle the current.
Ray

 

[Chromedome45]

No the Min is for either the Model 1 or the EI. Not both. Not enough current on the AC side for both. And as @Audronic said midi cables would not be a good choice due to the current they have to handle. Best to order a 5 pin DIN connector and a 4 conductor 20 gauge stranded wire cable.

If you wanted to handle both the EI and M1 use a 12.6 volt 3.5 to 4 amp transformer for the AC side the +5 and -5 supplies. BTW the -5 only uses 100mA. And a 1.2 amp should be adequate for the DC after it is rectified as your dad's had it set up which only powers the 12 volt line. And obviously you would need 5 pin 2 din cables.

So use the Max design.