gertk
Experienced Member
Well done!
Is the keyboard running on 5V only now or on the higher voltage ?
Is the keyboard running on 5V only now or on the higher voltage ?
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TV Typewriter replica project back on track
- Thread starter falter
- Start date
Go for it. Especially if it is anything vaguely SWTPC related! It is a huge irony the person we hear speaking the most, ourselves, sounds completely different to anyone else. And the only time we hear the 'real' us is when we do youtube videos (or become movie stars).
P.S. I dont make youtube videos because I hate the sound of my voice ;-)
falter
Veteran Member
It's running on 5V only. Don cleared that up for me - he said the 10-12V was only intended for capacitive keyboards, not hard contact like my Microswitch.
falter
Veteran Member
Yeah isn't that bizarre? I think there was a proverb or something that said 'you will never see your own face with your own eyes or hear your own voice with your own ears'. I think my voice as I hear it is fine.. I hate what it *actually* sounds like.
It was both that and the fact that there have been so many retro channels popping up that kept me from really trying to do some quality videos. I didn't want to look like a 'me-too' bandwagoner. But I realize there is a niche there - lots of computers and devices that remain uncovered because they're not Commodore or Atari.
falter
Veteran Member
Got one last remaining fly in the ointment.
Carriage Return does not work.
I suspect the reason is how it is wired. Right now i have one side of the switch connected to the 'CR' pin on the encoder, and the other for some reason I attached to +. I'm just not sure what the TVT would recognize. Right now we're getting a code of 0001111 (read A7-A1). I'm thinking based on the ASCII code table it should be either 0001010 (LF) or 0001101 (CR).
I'm not sure from my reading of the doc if the TVT understands those codes or not. Guess I can try hooking up the other side of the switch to 010 and 101 and see what happens?
EDIT: Yeah, it was 010. Now it all works!
Carriage Return does not work.
I suspect the reason is how it is wired. Right now i have one side of the switch connected to the 'CR' pin on the encoder, and the other for some reason I attached to +. I'm just not sure what the TVT would recognize. Right now we're getting a code of 0001111 (read A7-A1). I'm thinking based on the ASCII code table it should be either 0001010 (LF) or 0001101 (CR).
I'm not sure from my reading of the doc if the TVT understands those codes or not. Guess I can try hooking up the other side of the switch to 010 and 101 and see what happens?
EDIT: Yeah, it was 010. Now it all works!
falter
Veteran Member
Oh, and did I mention I picked up a TV? Regrettably FedEx treats 'fragile' stickers as a bull treats a red cape - the top plastic was broken. Not sure if the TV itself sustained damage.
It was a bit of a challenge finding anything that was verifiably pre-1974 (I wanted a TV that was definitely contemporary to the TVT when it came out). This one seemed to fit the bill. It appears to be 1973 from the model info. Unfortunately, the pictures on fleabay made the brightness look better than it was. Here is a shot taken in almost complete darkness. You can sort of read it:
I don't know if this is repairable or not -- might be the CRT itself being toast?
It was a bit of a challenge finding anything that was verifiably pre-1974 (I wanted a TV that was definitely contemporary to the TVT when it came out). This one seemed to fit the bill. It appears to be 1973 from the model info. Unfortunately, the pictures on fleabay made the brightness look better than it was. Here is a shot taken in almost complete darkness. You can sort of read it:
I don't know if this is repairable or not -- might be the CRT itself being toast?
gertk
Experienced Member
At least the black level is OK :D
Contrast and brightness controls work OK or are they 'noisy'?
How is the brightness without a signal (static/noise)
But inside there might be some additional adjustments for (sub)brightness, focus etc.
Also check the various voltages inside (filament supply could be low).
Contrast and brightness controls work OK or are they 'noisy'?
How is the brightness without a signal (static/noise)
But inside there might be some additional adjustments for (sub)brightness, focus etc.
Also check the various voltages inside (filament supply could be low).
falter
Veteran Member
Yes they seem to work.. I can crank the brightness but it's not very bright really. Static is ok but still pretty dim.
I'll pop it open this weekend.. always nervous with CRTs but hopefully there is something I can try adjusting. I believe this may be among the first of the solid state TVs... I think the 720 that went before it was transistor.
I'll pop it open this weekend.. always nervous with CRTs but hopefully there is something I can try adjusting. I believe this may be among the first of the solid state TVs... I think the 720 that went before it was transistor.
Chuck(G)
25k Member
Why transistor? My TVT was hooked into a "hot chassis" all-tube Zenith portable TV.
Been following this, just some random statements:
Good job! and nice that Don himself was involved
"Go for it. Especially if it is anything vaguely SWTPC related!" Agreed!!
I just gave away a video monitor from that era, the one that you would see in Byte or Kilobaud..sorry
"Why transistor? My TVT was hooked into a "hot chassis" all-tube Zenith portable TV." Ahhh 1979, just dont plug it in "backwards" :D
Best
Ted / KC9LKE
Good job! and nice that Don himself was involved
"Go for it. Especially if it is anything vaguely SWTPC related!" Agreed!!
I just gave away a video monitor from that era, the one that you would see in Byte or Kilobaud..sorry
"Why transistor? My TVT was hooked into a "hot chassis" all-tube Zenith portable TV." Ahhh 1979, just dont plug it in "backwards" :D
Best
Ted / KC9LKE
gertk
Experienced Member
What type of Sony TV is that ? Maybe a service manual can be found.
Chuck(G)
25k Member
I ran the TV from an isolation transformer, though a high-speed optoisolator could have served the same purpose. This was 1975.
HoJoPo
Veteran Member
I found a TV typewriter board today (empty sockets but otherwise complete), along with original documentation and receipt dated December, 1977 from the Byte Shop III in San Jose, CA. It was included in the boxes with the H8 system I was inventorying at a non-profit I volunteer for.
falter
Veteran Member
And the case is almost there..
This is the *third* case I've built. Each one I built I corrected different aspects. On the final one, I decided to go a tad longer than the original to give myself and my limited building skills some room to flex. But somehow I cocked it up anyway and for the THIRD time in a row, underestimated how much space the keyboard required. So with a hammer and metal table, I bent the back bend back out again, then bent it so it was slightly smaller inside. This gave me the just under 1/4 inch I needed to fit the keyboard in. This also meant that I was left with a scar where I'd routed (routered?) the space for the metal top to fit into the wood sides. But I think I'll live with that and just get some red oak patch and fill it.
I hope some day CHM will flip theirs over - I'd love to see if it's open like mine and if there are any details I missed in case construction.
I'm really nervous about firing it up again. I was so nervous about shorting on the case that I covered the inside of the top with electrical tape. Everywhere except one spot where the TVT appears to require a ground to chassis. Not sure why it needs that as it operates fine without it..
This is the *third* case I've built. Each one I built I corrected different aspects. On the final one, I decided to go a tad longer than the original to give myself and my limited building skills some room to flex. But somehow I cocked it up anyway and for the THIRD time in a row, underestimated how much space the keyboard required. So with a hammer and metal table, I bent the back bend back out again, then bent it so it was slightly smaller inside. This gave me the just under 1/4 inch I needed to fit the keyboard in. This also meant that I was left with a scar where I'd routed (routered?) the space for the metal top to fit into the wood sides. But I think I'll live with that and just get some red oak patch and fill it.
I hope some day CHM will flip theirs over - I'd love to see if it's open like mine and if there are any details I missed in case construction.
I'm really nervous about firing it up again. I was so nervous about shorting on the case that I covered the inside of the top with electrical tape. Everywhere except one spot where the TVT appears to require a ground to chassis. Not sure why it needs that as it operates fine without it..
falter
Veteran Member
So the good news is, the first power up of the TVT in its new case was promising - I had video immediately, cursor, you name it. But, nothing changes as I type.
The cursor moves - backwards or forwards as I wish - but yeah, it will not type at all. I suspected the Keep/Change switch - this TVT is a little on the fragile side. But the switch seems to operate properly and none of the contacts have broken. I checked pin 31, which goes low when Memory A is protected. It is low. It stays low no matter which position the Keep/Change switch is at. Based on my read of the manual, it should be high when Change is set. So it's like something is grounded that shouldn't be. I figured it might be something to do with the case.. but so far I haven't found anything grounded to the case metal that shouldn't be. I checked to make sure the encoder was working - it does seem to be changing bits as different keys are pressed, and A1-A7 seem to be changing on the TVT itself also. I'm at a bit of a loss, and not eager to pull this thing apart again to find the culprit.
The cursor moves - backwards or forwards as I wish - but yeah, it will not type at all. I suspected the Keep/Change switch - this TVT is a little on the fragile side. But the switch seems to operate properly and none of the contacts have broken. I checked pin 31, which goes low when Memory A is protected. It is low. It stays low no matter which position the Keep/Change switch is at. Based on my read of the manual, it should be high when Change is set. So it's like something is grounded that shouldn't be. I figured it might be something to do with the case.. but so far I haven't found anything grounded to the case metal that shouldn't be. I checked to make sure the encoder was working - it does seem to be changing bits as different keys are pressed, and A1-A7 seem to be changing on the TVT itself also. I'm at a bit of a loss, and not eager to pull this thing apart again to find the culprit.
falter
Veteran Member
Okay I'm feeling really dumb here.
I'm horrible with schematics. But I'm hoping I understand this now.
Here's the schematic:
The manual says if pin 31 is grounded, nothing can be written to Memory board A. Okay. So if I look at the schematic above as drawn, if the switch were in the position they're showing there, that connects 31 to ground, right?
I think there is an error that has been confusing me for half an hour. S3's current position in the schematic is grounding Protect A and grounding Enable A, right? That wouldn't work.. if Enable A is grounded nothing can be written. I think the schematic is wrong (again) and what 35 should be is Enable B. That seems to line up with how pin 35 is described in the manual.
Anyway, if I've got this understood correctly, my problem is something, somewhere, is grounding pin 31, regardless of what S4 and S3 are doing? I would therefore expect if I removed the jumper on the memory board that links to pin 31 and tied it to Enable A's jumper, I should be able to write again?
I just can't figure out what would be grounding 31. I can't see it making any contact with the metal case where it shouldn't be. All the other switches work normally. But no matter what position S4 is in, 31 is grounded.
I'm horrible with schematics. But I'm hoping I understand this now.
Here's the schematic:
The manual says if pin 31 is grounded, nothing can be written to Memory board A. Okay. So if I look at the schematic above as drawn, if the switch were in the position they're showing there, that connects 31 to ground, right?
I think there is an error that has been confusing me for half an hour. S3's current position in the schematic is grounding Protect A and grounding Enable A, right? That wouldn't work.. if Enable A is grounded nothing can be written. I think the schematic is wrong (again) and what 35 should be is Enable B. That seems to line up with how pin 35 is described in the manual.
Anyway, if I've got this understood correctly, my problem is something, somewhere, is grounding pin 31, regardless of what S4 and S3 are doing? I would therefore expect if I removed the jumper on the memory board that links to pin 31 and tied it to Enable A's jumper, I should be able to write again?
I just can't figure out what would be grounding 31. I can't see it making any contact with the metal case where it shouldn't be. All the other switches work normally. But no matter what position S4 is in, 31 is grounded.
falter
Veteran Member
So much for that theory.
To test whether I had a problem with the keep/change switch grounding, I removed the jumper on Memory Board A for protect, and connected it directly to pin 34, which also goes high when Page A memory is selected and ready to write. It did not work. Even though I could see at the other end of that jumper that it was high now, there's nothing happening. There's also no Update coming on line 51 from the cursor board as I type. So no characters change, although the cursor moves each time a key is pressed.
I guess I'm going to have to give up and pull this thing from the case, which will be a chore.. but yeah.. I don't know what's going on here.
To test whether I had a problem with the keep/change switch grounding, I removed the jumper on Memory Board A for protect, and connected it directly to pin 34, which also goes high when Page A memory is selected and ready to write. It did not work. Even though I could see at the other end of that jumper that it was high now, there's nothing happening. There's also no Update coming on line 51 from the cursor board as I type. So no characters change, although the cursor moves each time a key is pressed.
I guess I'm going to have to give up and pull this thing from the case, which will be a chore.. but yeah.. I don't know what's going on here.
falter
Veteran Member
Okay so I've recovered things somewhat. I thought the electrical tape I had coated the underside of the metal case lid with would be sufficient to keep anything from inadvertently shorting, however after removing the TVT I discovered a few things like the self test posts had scratched their way through the tape and thus brought parts of the PCB into contact with the metal. I also discovered that the 2518 I had on the Memory board had gone bad somehow. A replacement immediately got things working better.
So now I'm back to yet another run around with the ASCII encoder, I think. It is not producing the right ASCII codes again, and A1-A3 produce a weird tone on my logic probe along with faintly lit HI and LO lights. I think something is shorting. I disconnected the TVT and it persisted so it's not that. I'm guessing keyboard? Far as I could tell only 2 wires broke while I was installing it into the case. Don't see any shorts or any wrongly crossed wires. Agh! The worst part of this is, when I figure this out after the inevitable 20 hours of headscratching, I have to try and cram this thing back into its case without it breaking again!
So now I'm back to yet another run around with the ASCII encoder, I think. It is not producing the right ASCII codes again, and A1-A3 produce a weird tone on my logic probe along with faintly lit HI and LO lights. I think something is shorting. I disconnected the TVT and it persisted so it's not that. I'm guessing keyboard? Far as I could tell only 2 wires broke while I was installing it into the case. Don't see any shorts or any wrongly crossed wires. Agh! The worst part of this is, when I figure this out after the inevitable 20 hours of headscratching, I have to try and cram this thing back into its case without it breaking again!
Chuck(G)
25k Member
If you need to insulate the case, consider some self-adhesive film, say by MacTac. I've seen the stuff used to protect the underside of skid plates on ORVs.