jeffa
New Member
Hi guys,
I recently stumbled upon a Model 4 in a Thrift store with a $5 price tag on it, and found myself putting in in a cart a few moments later. ;-) I learned Basic on a Model III back in the 9th grade (1982), and love classic computers and couldn't resist myself! :D
When I got it home, it would power on, but with seemingly random characters on the screen. I opened it up, and first tried to just re-seat every socketed chip. That changed a little bit, but not much. (different characters... ;-) )
I noticed that the chip leads were somewhat oxidized and discolored, so I took each one out again, and scraped the leads a bit with an xacto until they were shiny and put them back in. ;-) When I got done, now I had a completely blank screen... It's been a long time since I used one, so I fumbled around and finally stumbled upon 'break-reset' to get the 'CASS?" prompt. Progress!!!
I googled my brains out and found Ira's TRS-80 site (http://www.trs-80.com/) and after a few emails back and forth with him, I ended up engaging his services for a set of discs. ;-) And at Ira's suggestion, I cleaned the sliders on the drive and lubed them up (they were both frozen as Ira had predicted they might be).
Once I got the disks, I fired it up, and it works!!! But only drive 0 works - Drive 1 is not working. After doing some troubleshooting (including swapping the drive controller boards between the two drives) I determined that the drive's controller board is ok, but something is physically wrong with the drive itself - the stepper, the spindle motor, or the head...
So I googled around to see what I could do... And I found Larry Kramer's document (www.retrotechnology.com/herbs_stuff/Model4_35_Drives.pdf) that documents how to use 3.5" floppy drives with our computes. So I set off to find some 3.5" floppy drives to try it out!!! After a couple of hours work and a stack of floppy drives, I had two working 720K drives with a custom cable. ;-)
So then I began to troubleshoot the 5-1/4 Texas Peripherals drive more. I noticed that the stepper motor for the head positioning was not working right - instead of stepping, it was 'jittering' back and forth a bit. I measured the resistance of the coils, and found one to be open... It just so happens that I had a 'spare' stepper motor from a full-height 5-1/4" floppy that I "gutted' for the stepper motor years ago (dummy, I know!) -- It even has the original connector and '12' written on it, just like the TP drive's stepper, so it was probably from a TP drive as well. ;-) Anyways - I swapped out the stepper motor (quite a feat getting the old one out and the new one in without disassembling things and knocking the alignment off...) - and although it now stepped properly, the drive still doesn't work. :-(
So more googling, and I found several promising sites on how to connect a 360K 5-1/4" floppy, and/or a 1.2MB HD floppy that is 'switchable' to 300rpm, but as luck would have it, I threw out some old 'pc' hardware about a year ago, and some of them had 5-1/4" floppies.
The only 5-1/4" drive I managed to find was a Canon dual-floppy - model MD511-V6 - with both a 1.2MB 5-1/4" drive and a 1.44MB 3.5" drive in one enclosure. I opened it up and found a nicely labelled block on the spindle motor board (ie: [x]360 [ ]300) and un-soldered the resistor/shunt from the 360 pads and moved it to the 300 pads, but it still doesn't work in my M4 - I had forgotten about the 40track vs 80track stepping... Doh!
Now, I do realize the drive would basically only be good for 'reading' disks, since the heads are thinner than the 40-track drive, but it would have been a neat addition to my M4. ;-) (I've thought about flashing a little 8-pin PIC to provide a hardware double-step - do you think it's worth the effort?) Oh, and the 3.5" drive in the combo works great.
I forgot to mention - it's one of the 1st Model 4's, a non-Gate-array model - it's a White CRT, and the arrow keys are not grouped -- up/down are on the left, and left/right are on the right side under 'break'. The RS-232 port faces down. ;-)
So at this point, I'm still looking around for a [cheap] 5-1/4" "PC" floppy drive that I can convert to my M4 - preferably a 360k drive so the head width is the same. ;-)
And I *might* even build myself an IDE interface - the one I found is by Andrew Quinn (http://www.qsl.net/zl1wjq/trside1.htm) - have any of you done that? ;-)
Jeff
I recently stumbled upon a Model 4 in a Thrift store with a $5 price tag on it, and found myself putting in in a cart a few moments later. ;-) I learned Basic on a Model III back in the 9th grade (1982), and love classic computers and couldn't resist myself! :D
When I got it home, it would power on, but with seemingly random characters on the screen. I opened it up, and first tried to just re-seat every socketed chip. That changed a little bit, but not much. (different characters... ;-) )
I noticed that the chip leads were somewhat oxidized and discolored, so I took each one out again, and scraped the leads a bit with an xacto until they were shiny and put them back in. ;-) When I got done, now I had a completely blank screen... It's been a long time since I used one, so I fumbled around and finally stumbled upon 'break-reset' to get the 'CASS?" prompt. Progress!!!
I googled my brains out and found Ira's TRS-80 site (http://www.trs-80.com/) and after a few emails back and forth with him, I ended up engaging his services for a set of discs. ;-) And at Ira's suggestion, I cleaned the sliders on the drive and lubed them up (they were both frozen as Ira had predicted they might be).
Once I got the disks, I fired it up, and it works!!! But only drive 0 works - Drive 1 is not working. After doing some troubleshooting (including swapping the drive controller boards between the two drives) I determined that the drive's controller board is ok, but something is physically wrong with the drive itself - the stepper, the spindle motor, or the head...
So I googled around to see what I could do... And I found Larry Kramer's document (www.retrotechnology.com/herbs_stuff/Model4_35_Drives.pdf) that documents how to use 3.5" floppy drives with our computes. So I set off to find some 3.5" floppy drives to try it out!!! After a couple of hours work and a stack of floppy drives, I had two working 720K drives with a custom cable. ;-)
So then I began to troubleshoot the 5-1/4 Texas Peripherals drive more. I noticed that the stepper motor for the head positioning was not working right - instead of stepping, it was 'jittering' back and forth a bit. I measured the resistance of the coils, and found one to be open... It just so happens that I had a 'spare' stepper motor from a full-height 5-1/4" floppy that I "gutted' for the stepper motor years ago (dummy, I know!) -- It even has the original connector and '12' written on it, just like the TP drive's stepper, so it was probably from a TP drive as well. ;-) Anyways - I swapped out the stepper motor (quite a feat getting the old one out and the new one in without disassembling things and knocking the alignment off...) - and although it now stepped properly, the drive still doesn't work. :-(
So more googling, and I found several promising sites on how to connect a 360K 5-1/4" floppy, and/or a 1.2MB HD floppy that is 'switchable' to 300rpm, but as luck would have it, I threw out some old 'pc' hardware about a year ago, and some of them had 5-1/4" floppies.
The only 5-1/4" drive I managed to find was a Canon dual-floppy - model MD511-V6 - with both a 1.2MB 5-1/4" drive and a 1.44MB 3.5" drive in one enclosure. I opened it up and found a nicely labelled block on the spindle motor board (ie: [x]360 [ ]300) and un-soldered the resistor/shunt from the 360 pads and moved it to the 300 pads, but it still doesn't work in my M4 - I had forgotten about the 40track vs 80track stepping... Doh! Now, I do realize the drive would basically only be good for 'reading' disks, since the heads are thinner than the 40-track drive, but it would have been a neat addition to my M4. ;-) (I've thought about flashing a little 8-pin PIC to provide a hardware double-step - do you think it's worth the effort?) Oh, and the 3.5" drive in the combo works great.
I forgot to mention - it's one of the 1st Model 4's, a non-Gate-array model - it's a White CRT, and the arrow keys are not grouped -- up/down are on the left, and left/right are on the right side under 'break'. The RS-232 port faces down. ;-)
So at this point, I'm still looking around for a [cheap] 5-1/4" "PC" floppy drive that I can convert to my M4 - preferably a 360k drive so the head width is the same. ;-)
And I *might* even build myself an IDE interface - the one I found is by Andrew Quinn (http://www.qsl.net/zl1wjq/trside1.htm) - have any of you done that? ;-)
Jeff
