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TRS-80 Model 26-1006D Video Problems

Jimmy

Jimmy

Veteran Member
Joined
Feb 19, 2012
Messages
594
Location
Fort Walton Beach, Fl
I recently acquired two TRS-80 what I believe are Model 1's. I made a video cable and a forum member loaned me a power supply to check to see if either machine would power up. One is labeled 26-1006D and the other is labeled 26-1006G. The D model has a numeric keyboard, has a memory mod and also a modification with a cable extention out the expanision port, that I have not idea what is. The video on the G works great, but on the D is just horizontal uneven line. I know nothing about these old machines.

I am posting pictures of the D model.

Any advice on where to start would be greatly appreciated.

Thanks,

Jimmy

IMG_1680.jpgIMG_1676.jpgIMG_1678.jpgIMG_1679.jpg
 
I'm not familiar enough with the Model I's video hardware to offer much advice there, but I can tell you what that plug modification is: the early models of the Expansion Interface had some pretty severe reliability problems and Radio Shack offered several different fixes. The first of those fixes involved a "buffered" cable (instead of a plain 40 pin cable the cable had a "lump" in the middle containing what is essentially an amplifier), and when that wasn't enough a second modification separated several vital memory refresh signals onto a shielded cable with a DIN connector in the middle.

(The final fix was to revamp the Expansion Interface board itself to buffer and regenerate several of the most critical signals internally, dispensing with the need for the buffered cable or DIN modification.)

It's sort of a shame you don't have the matching E.I.
 
Ian:

Thanks a miilion, I will replace the chip when I get back in town. Since I know at least one of the machines powers on (Thanks to ChromeDome for loaning me a power brick), I am going to tackle making a power adapter from your post.

Jimmy
 
Ian:

I replaced Z5 with a 74HC00 but still have lines, I do not believe they are scrolling as bad before I replaced the chip, but still no text.

Thanks,

Jimmy
 
3 chips combine the image to lock H and V, try changing Z6, a 74C04, and see if the lines change.

In very severe situations I've had to change Z5, Z6 and the other 74C04 (whos part number escapes me at the moment) to get an image.
 
Ian:

Thank you for the reply, I could write what I know about TRS-80s on the head of a pin, but I am learning. I will the change the chip, see if I can find something for Z6 on the net.

Jimmy
 
Jimmy:

It's been a long time since I've had a Model 1 around to play with. But, before you start tearing into components, check and see if there's a horizontal adjustment (pot) on that monitor. Also, it looks like you have an Apple monitor attached where the original Model 1 had a RCA B&W. There may or may not be a some compatibility issues - probably not, but worth mentioning.
 
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Orange:

Thank you, I actually was given two of the TRS-80s one works fine when hooked up to the apple monitor. The one that has display problems also has a memory modification and what I have been told is a cable for an interface expansion.

Thanks, I welcome any ideas that will help.

Jimmy
 
Jimmy said:
Orange:

Thank you, I actually was given two of the TRS-80s one works fine when hooked up to the apple monitor. The one that has display problems also has a memory modification and what I have been told is a cable for an interface expansion.

Thanks, I welcome any ideas that will help.

Jimmy
Click to expand...

Do you know the nature of that memory mod?
 
Right, Z57 is the other 74C04 responsible for the video display. If after replacing those the thing still isn't right I start looking at Q1 and Q2, and on the occasion I have seen capacitors C2, C7, C20, C21, C26 and C27 can cause problems. All the parts are cheap and easy to procure but hopefully things will start looking up withn Z57 changed.

Ian.
 
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