Image Map Image Map
Page 1 of 2 12 LastLast
Results 1 to 10 of 19

Thread: Tandy Model III Repair Questions

  1. #1
    Join Date
    Apr 2019
    Location
    St. Louis
    Posts
    16

    Default Tandy Model III Repair Questions

    Hello! Just picked up a Tandy Model III that is semi working and had a few questions. It is a disk based system with 16K and two floppy drives. The good news is it boots to cass? with break+reset! Bad news is the keyboard and floppy drives do not seem to be working. I suspect a dead power supply for the floppy drive as they flash the led then turn off. I plugged them into another PSU with normal molex plugs and the drives do spin up correctly. No idea on reading disks yet. I plan on cleaning the heads and greasing the rails. The keyboard I plan on de-soldering, cleaning, and polishing the metal contacts with stainless metal polish. Also on first boot the screen is filled with the same repeating charter. It's different each time and is only on first boot. Resting (even without holding break) drops into cassette basic. I'm hoping it's related to the PSU issues unless someone has something further to add. So I'm going to go ahead and re-cap both power supplies as I do not want to have them blow latter down the line. I don't seen any blown ones as far as I can tell, but I think it would be easier just to replace all of them given the age. Now here is the question. I'm fairly new to capacitors (not so much to soldering) and am wanting to replace them with something that is more reliable. I found a chart for all the capacitors, but it doesn't list what types they are. I narrowed it down (I think) to Electrolytic, Ceramic, and Film? It seems to me that these are the most common and that now I see poly caps recommended to replace most of the other types. Are poly caps Polymer Capacitors? These look like they are a newer type not around when the computer was made. Again I could be way off here. I also narrowed down that the white/yellow blocky ones are usually first to blow. These are listed everywhere as X 0.1uF RIFA (now Kemet) caps. Most of what I found advised using an X2, but that as far as I have gotten on these. Are they Film? Poly? I really just need to know the category to select on digikey to order new ones. I put the specifications down below. I will leave this with what caps do I get question for now. After that I will see what is working and what is not. Here is the manual form the internet archive I pulled this info from: https://ia801705.us.archive.org/28/i...Tandy_text.pdf

    C1 - 2200pF, 250VAC
    C2 - O.O1uF, 1KV
    C3 - 2200pF, 25GVAC
    C4 - 0.22uF, 250V
    C5 - 47uF, 250V
    C6 - 47uF, 250V
    C7 - 220uF, 10V
    C8 - 4700pF, 1KV
    C9 - 0.01uF, 1KV
    C10 - 0.22uF, 1O0V
    C11 - 1000uF, 25V
    C12 - 1000uF, 25V
    C13 - 1000uF, 25V
    C14 - 330uF, 16V
    C15 - 2200uF, 16V
    C16 - 330uF, 16V
    C17 - 470uF, 25V
    C18 - 0.022uF, 50V
    C19 - 0.22uF, 100V
    C21 - 0.1uF, 250VAC

  2. #2
    Join Date
    Jun 2018
    Location
    Pacific NW in the islands
    Posts
    107

    Default

    cleaning disk drive heads is good, IMHO greasing rails in a drive is not so good. definitely clean them. if they're pitted or rough you can use crocus cloth to polish them up and smooth them out (we used crocus cloth in service at RS to do this and to smooth printer rails). use a light touch.. use something like 90.n% isopropyl alcohol to clean them up after that, and you can use that alcohol on the heads, too. the reason not to lubricate rails in drives, or worm gears in the 8" variety, is two fold. first, you risk slinging lubricant all over the inside of the drive an onto the media and maybe head/s. the other reason is that it attracts dust and grit and pretty soon your drive is needing to be fixed again.

    i've never had to lubricate any surfaces in a drive, but most of my drive work was 30+ years ago when those drives were relatively new. today is a different story. so now that i've told you not to lubricate, i'm going to add unless you absolutely have to in order to get the drive working. service manuals, either from radio shack/tandy or the original manufacturer are available--most online i think. good to read up before you get started and they should address any parts requiring lubrication.

    also, don't remove any adjustment screws--you can read the service manual or the OEM drive manual to find what those are for your particular drive/s. alignment diskettes are no longer produced and i expect that they're pretty scarce--they can not be duplicated on regular drives. so if you mess with adjustments that would require an alignment diskette to properly set, you've given yourself another problem.

    i'd also recommend against stainless steel polish for cleaning contacts of any kind. there are several fine products available for cleaning contacts--i use the Deoxit. it comes in several formulations and you can pick the one that matches what you're wanting to clean. amazon has starter/sample packs if you want to go that route. they have other good products as well. no WD40!

    anyway drives, especially the 5 1/4" variety, are not difficult to work on. just read up, take your time and have fun with it.

    probably, someone with more recent drive repair experience in light of how these old drives have aged can give you more specifics.

  3. #3
    Join Date
    Jun 2013
    Location
    Melbourne, Australia
    Posts
    165

    Default

    Quote Originally Posted by psg4 View Post
    Just picked up a Tandy Model III that is semi working and had a few questions. It is a disk based system with 16K and two floppy drives.
    Are you sure it only has 16K RAM? I'm pretty sure you need at least 32K (preferably the full 48K) to run a disk system.

    From the BASIC prompt, try "PRINT MEM" to see how much RAM you have (after getting the keyboard working, of course!).

  4. #4
    Join Date
    Apr 2019
    Location
    St. Louis
    Posts
    16

    Default

    I do plan to use isopropyl alcohol to on a Que-Tip to clean the head and rails of the drive first. (Actually probably all of the insides as well will get a good amount of it to remove the grit) I will definitely wait on lubrication to see if I can get away without it. If not I was going to use a dab of white lithium grease on a Que-Top for the rails. I won't have a way to even test the drive until the PSU is working again. I have a can of electrics contact cleaner if that will work for the keys contact plates? I also have a can of aluminum/sliver/stainless/etc. tarnish remover if that will work in place of that. I plan to use isopropyl on a Que-Tip first then will move to contact cleaner if they are still too dirty. Thanks for the help!

  5. #5
    Join Date
    Apr 2019
    Location
    St. Louis
    Posts
    16

    Default

    That's a very good point. The badge says 16K, but it could have been upgraded. It has clearly been opened a few times in the past for repairs so it's possible it was upgraded by the prior owner.

  6. #6
    Join Date
    Apr 2019
    Location
    St. Louis
    Posts
    16

    Default

    Interesting. It might have more. It has been opened in the past for sure. I was going off the badge on the front sating 16K, but it could have been upgraded at some point in time. I will have to check. Thanks!

  7. #7
    Join Date
    Apr 2019
    Location
    St. Louis
    Posts
    16

    Default

    OK lots of good information. I plan to clean just about everything with isopropyl first. I will save greasing the rails if a cleanup doesn't work. I was going to use White Lithium Grease for that if I need to. I plan on only using a small amount on a Quetip. As for the keys will electric contact cleaner work in place of Deoxit? I also have some metal tarnish remover for steel/aluminum/sliver if that will not work.

  8. #8
    Join Date
    Mar 2016
    Location
    Pikesville, Maryland
    Posts
    216

    Default

    Quote Originally Posted by psg4 View Post
    Hello! Just picked up a Tandy Model III that is semi working and had a few questions. It is a disk based system with 16K and two floppy drives. The good news is it boots to cass? with break+reset! Bad news is the keyboard and floppy drives do not seem to be working. I suspect a dead power supply for the floppy drive as they flash the led then turn off. I plugged them into another PSU with normal molex plugs and the drives do spin up correctly. No idea on reading disks yet. I plan on cleaning the heads and greasing the rails. The keyboard I plan on de-soldering, cleaning, and polishing the metal contacts with stainless metal polish. Also on first boot the screen is filled with the same repeating charter. It's different each time and is only on first boot. Resting (even without holding break) drops into cassette basic. I'm hoping it's related to the PSU issues unless someone has something further to add. So I'm going to go ahead and re-cap both power supplies as I do not want to have them blow latter down the line. I don't seen any blown ones as far as I can tell, but I think it would be easier just to replace all of them given the age. Now here is the question. I'm fairly new to capacitors (not so much to soldering) and am wanting to replace them with something that is more reliable. I found a chart for all the capacitors, but it doesn't list what types they are. I narrowed it down (I think) to Electrolytic, Ceramic, and Film? It seems to me that these are the most common and that now I see poly caps recommended to replace most of the other types. Are poly caps Polymer Capacitors? These look like they are a newer type not around when the computer was made. Again I could be way off here. I also narrowed down that the white/yellow blocky ones are usually first to blow. These are listed everywhere as X 0.1uF RIFA (now Kemet) caps. Most of what I found advised using an X2, but that as far as I have gotten on these. Are they Film? Poly? I really just need to know the category to select on digikey to order new ones. I put the specifications down below. I will leave this with what caps do I get question for now. After that I will see what is working and what is not. Here is the manual form the internet archive I pulled this info from: https://ia801705.us.archive.org/28/i...Tandy_text.pdf

    C1 - 2200pF, 250VAC
    C2 - O.O1uF, 1KV
    C3 - 2200pF, 25GVAC
    C4 - 0.22uF, 250V
    C5 - 47uF, 250V
    C6 - 47uF, 250V
    C7 - 220uF, 10V
    C8 - 4700pF, 1KV
    C9 - 0.01uF, 1KV
    C10 - 0.22uF, 1O0V
    C11 - 1000uF, 25V
    C12 - 1000uF, 25V
    C13 - 1000uF, 25V
    C14 - 330uF, 16V
    C15 - 2200uF, 16V
    C16 - 330uF, 16V
    C17 - 470uF, 25V
    C18 - 0.022uF, 50V
    C19 - 0.22uF, 100V
    C21 - 0.1uF, 250VAC

    Can you provide any photos of the machine showing what you describe ... will heip immensely .... I maintain a HUGE supply of replacement parts for the Model 3,4,4D,4P computers
    I have stripped down about 6 machines to "bare case" - so I have just about any part of these machines
    Contact me at JAYNEWIRTH@VERIZON.NET if you need anything to help you out

  9. #9
    Join Date
    Mar 2016
    Location
    Pikesville, Maryland
    Posts
    216

    Default

    Squirt some 3-n-1 oil on the rails then wipe with tips

  10. #10
    Join Date
    Mar 2016
    Location
    Pikesville, Maryland
    Posts
    216

    Default

    Quote Originally Posted by psg4 View Post
    That's a very good point. The badge says 16K, but it could have been upgraded. It has clearly been opened a few times in the past for repairs so it's possible it was upgraded by the prior owner.

    If you need replacement badges for the Model III ---- I have the case and memory badges in stock !!!

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •