Dwight Elvey
Veteran Member
I've been bring my old Poly88 back to life. I'm making slow progress but mostly going slow.
The keyboard I have has an interesting modification. I'm not sure why it was there. It had a switch on the side that connected two of the data out pins together of the KR2376. The funny thing is it didn't even wire these pins out to the data pins of the Poly88. It looked like work I'd done years ago but who knows. I removed the switch and ran the wires that looked to be grounded to the Poly88 and now it see numbers as well as other characters. Anyway, the switch was old and didn't work. I'd like to find a way to make a shift lock that didn't shift the numbers but may have to live with it as it is. I wish I knew what that switch did?
Ahh, the smell of a large tantalum going up in smoke. It was a 100uf. There were two of them in parallel right next to each other so if figured it would work fine with just one. It really burned good. There was a nice flame I had to blow out and black smudges all along the board. What a mess. This was on the CMOS memory board I was talking about. I cleaned up the soot and the board seems to work fine.
I'm about ready to see if some old tapes I have have got any information left on them. Some are tapes I did and some are others work. For those using old machine with cassettes, a word to the wise. Don't store cassette tape wound with fast forward of fast reverse. Always store them packed slowly and smoothly with the play. Only use the fast while you are actively going to run that part again in a few minutes. The loose packing leaves wrinkles at the edges and some time wrinkles across the tape, that cause dropouts.
Hopefully, I can repack them and get them to read after sitting some. This usually works but these have been sitting for years.
The Poly88 did two speed modes for recording. One was the typical KC byte format at slow speed. The other was a high speed 1200 baud rate. It required a higher quality tape recorder. I've been bring an old Superscope Marrantz back to life. These old Marrantz were built like tanks. I've got belts on order but made some temporary belts from rubber bands and super glue. So far they seem to work OK. The deck has issues with the auto shut off and no fast reverse. I need to look into the fast reverse but I can live with the auto shut off for a while. It stops the play by releasing the pinch roller but sometimes the motor keeps running. It looks like some old grease keeping one of the levers from moving, freely.
So far all the old memory seems to be working. The memory on the video board looks good, the memory on the CPU board looks good and the ones on the CMOS board look good ( although, the ones at the edge have smoke and fire damage ). I'm quite surprised because the last time I pulled this stuff out, it required some chips to be replaced ( about 10-15 years back ). Maybe, I got all the infant mortality out and the rest will last for another 100 years.
It is interesting that I have the issue with the vertical pulse being too long as mentioned in one of the earlier articles. It is causing the first few lines to drag to the left some as the horizontal resynchs. I need to look at the schematic for the video to see if there is a convenient modification that can be done.
Enough fun stories, back to hacking it some more.
Dwight
The keyboard I have has an interesting modification. I'm not sure why it was there. It had a switch on the side that connected two of the data out pins together of the KR2376. The funny thing is it didn't even wire these pins out to the data pins of the Poly88. It looked like work I'd done years ago but who knows. I removed the switch and ran the wires that looked to be grounded to the Poly88 and now it see numbers as well as other characters. Anyway, the switch was old and didn't work. I'd like to find a way to make a shift lock that didn't shift the numbers but may have to live with it as it is. I wish I knew what that switch did?
Ahh, the smell of a large tantalum going up in smoke. It was a 100uf. There were two of them in parallel right next to each other so if figured it would work fine with just one. It really burned good. There was a nice flame I had to blow out and black smudges all along the board. What a mess. This was on the CMOS memory board I was talking about. I cleaned up the soot and the board seems to work fine.
I'm about ready to see if some old tapes I have have got any information left on them. Some are tapes I did and some are others work. For those using old machine with cassettes, a word to the wise. Don't store cassette tape wound with fast forward of fast reverse. Always store them packed slowly and smoothly with the play. Only use the fast while you are actively going to run that part again in a few minutes. The loose packing leaves wrinkles at the edges and some time wrinkles across the tape, that cause dropouts.
Hopefully, I can repack them and get them to read after sitting some. This usually works but these have been sitting for years.
The Poly88 did two speed modes for recording. One was the typical KC byte format at slow speed. The other was a high speed 1200 baud rate. It required a higher quality tape recorder. I've been bring an old Superscope Marrantz back to life. These old Marrantz were built like tanks. I've got belts on order but made some temporary belts from rubber bands and super glue. So far they seem to work OK. The deck has issues with the auto shut off and no fast reverse. I need to look into the fast reverse but I can live with the auto shut off for a while. It stops the play by releasing the pinch roller but sometimes the motor keeps running. It looks like some old grease keeping one of the levers from moving, freely.
So far all the old memory seems to be working. The memory on the video board looks good, the memory on the CPU board looks good and the ones on the CMOS board look good ( although, the ones at the edge have smoke and fire damage ). I'm quite surprised because the last time I pulled this stuff out, it required some chips to be replaced ( about 10-15 years back ). Maybe, I got all the infant mortality out and the rest will last for another 100 years.
It is interesting that I have the issue with the vertical pulse being too long as mentioned in one of the earlier articles. It is causing the first few lines to drag to the left some as the horizontal resynchs. I need to look at the schematic for the video to see if there is a convenient modification that can be done.
Enough fun stories, back to hacking it some more.
Dwight