General Stuff(tm)

[rubber_jonnie]

I see you caved and went for the U1MB then 😁

[stephen_usher]

Yeah. :-)

The documentation is a bit pants isn't it, unless you want to update the firmware or do advanced stuff.

The basics such as finding the key presses to get to the set-up menu (reset-start-help) I had to look at YouTube videos to find. Even wiring it up I had to use fizzy images on blog posts and it wasn't explicitly stated that the red line on the ribbon cable went to the pin 1 end of the sockets either. The docs are more like release notes than anything else.

Seeing as I have no background in the A8 hardware scene I still have no idea what the various RAM modes are as they're just named after original upgrades.

[rubber_jonnie]

Yeah. :-)

The documentation is a bit pants isn't it, unless you want to update the firmware or do advanced stuff.

Yeah, I've seen better. Having done two now I'm lucky enough to have a reference, but the first one was fun and games. My two (800XL and 65XE) also have PokeyMax stereo and VBXL/XE so getting crowded inside.

If you happen to add those and replace the video socket with an ST type that uses a 1088XEL type cable for SCART and stereo finding the wiring for that is a nightmare.

The basics such as finding the key presses to get to the set-up menu (reset-start-help) I had to look at YouTube videos to find. Even wiring it up I had to use fizzy images on blog posts and it wasn't explicitly stated that the red line on the ribbon cable went to the pin 1 end of the sockets either. The docs are more like release notes than anything else.

Seeing as I have no background in the A8 hardware scene I still have no idea what the various RAM modes are as they're just named after original upgrades.

Did you get the instructions from here: U1MB on Lothareks site

Those are what I used and were OK ish.

I have an incognito Gold in my Atari 800 and it is the equivalent of the U1MB for that model and whilst I found the install instructions better it was similarly difficult to find instructions. Reset + the Atari Key isn't obvious for getting to the menu.

I do prefer the Incognito as it offers XL/XE and Colleen (400/800) modes.

I'm wondering if the firmware has changed as I only usually press Reset + Help to get to the menu. Must admit I haven't updated my firmware lately.

The well known upgrades from back in the day were Rambo (256 or 512K), Compy Shop (256 or 320K) and Newell (256 or 1MB) and if you look at the 400 there was the Axlon (128K).

There are others the U1MB supports IIRC, but those are the common ones I remember. There are some games that do support 1MB and there are a lot of demos too, have a look at Numen which requires 320K. Might need stereo though not 100% sure. It's in the stuff I gave you.

[stephen_usher]

I've had time to look at the U1MB upgrade for the Atari 800XL and play with it. I've also had a chance, unlike in the rush on Friday afternoon, to take some better pictures of the installation.

Let's start with the installation.

First of all, the 3D printed mounting frame.

This bolts into two of the RF shield fixing holes, meaning that no new holes have to be drilled into the PCB, making this fully reversible. The I routed the ROM IDC cable out towards the front, which did mean that it was pushing on the frame a bit but that's not a problem. It makes the cable routing a bit cleaner IMHO.

IMG_4895.jpeg

IMG_4896.jpeg

I cut the other four flying wires to length and the longest one I hot glued in position.

IMG_4897.jpeg

The IDC cables lay pretty flat now with them laying over the add-on PCB.

IMG_4898.jpeg

If I had been designing the PCB I would have made the two IDC connectors 90 90 degree ones and both facing toward the front of the machine. The cables would have then lain flat (mostly) and if the four other wires had been on a right angled, four way Dupont socket at the rear would have made the whole thing a lot cleaner and look less unsightly too.

I've used M3 machine screw pushed up through the lower RF shield and secured by nuts. This stiffens the whole PCB, which should protect it, and it also allows the fitting of the grounding lugs for the expansion port. Once the washers arrive later today I'll finally finish everything on the inside and button it up. I've kept the upper shield, screws and the ROM and MMU chips so that in future this can all be reversed.

[rubber_jonnie]

I've had time to look at the U1MB upgrade for the Atari 800XL and play with it. I've also had a chance, unlike in the rush on Friday afternoon, to take some better pictures of the installation.

Let's start with the installation.

First of all, the 3D printed mounting frame.

This bolts into two of the RF shield fixing holes, meaning that no new holes have to be drilled into the PCB, making this fully reversible. The I routed the ROM IDC cable out towards the front, which did mean that it was pushing on the frame a bit but that's not a problem. It makes the cable routing a bit cleaner IMHO.


IMG_4895.jpeg


IMG_4896.jpeg


I cut the other four flying wires to length and the longest one I hot glued in position.


IMG_4897.jpeg


The IDC cables lay pretty flat now with them laying over the add-on PCB.


IMG_4898.jpeg


If I had been designing the PCB I would have made the two IDC connectors 90 90 degree ones and both facing toward the front of the machine. The cables would have then lain flat (mostly) and if the four other wires had been on a right angled, four way Dupont socket at the rear would have made the whole thing a lot cleaner and look less unsightly too.

I've used M3 machine screw pushed up through the lower RF shield and secured by nuts. This stiffens the whole PCB, which should protect it, and it also allows the fitting of the grounding lugs for the expansion port. Once the washers arrive later today I'll finally finish everything on the inside and button it up. I've kept the upper shield, screws and the ROM and MMU chips so that in future this can all be reversed.

Nice, and a much neater installation than either of mine :dizzy:

The bracket does make it very neat for sure, I can't recall how mine are done. There are definitely design improvements that could be made. For one I find the cables are way too long, there seems to be no need for it.

[stephen_usher]

The bracket does make it very neat for sure, I can't recall how mine are done. There are definitely design improvements that could be made. For one I find the cables are way too long, there seems to be no need for it.

I think most of the need is so that they can be twisted and folded several times just to get the correct orientation for the sockets!

[rubber_jonnie]

The bracket does make it very neat for sure, I can't recall how mine are done. There are definitely design improvements that could be made. For one I find the cables are way too long, there seems to be no need for it.

I think most of the need is so that they can be twisted and folded several times just to get the correct orientation for the sockets!

Very likely...

I think if the install was a bit more 'standardised' they could likely get around some of that.

[stephen_usher]

Very likely...

I think if the install was a bit more 'standardised' they could likely get around some of that.

Indeed, and change the shape of the PCB so that it will fit low, beside the chip sockets... Lots of things could be improved, but won't be.

[rubber_jonnie]

Very likely...

I think if the install was a bit more 'standardised' they could likely get around some of that.

Indeed, and change the shape of the PCB so that it will fit low, beside the chip sockets... Lots of things could be improved, but won't be.

I don't see anything much changing other than firmware!

Also I think Lotharek and FJC fell out so the firmware may not be the same.

[stephen_usher]

Over the last couple of days I've been working on DEC LK201 terminal keyboard.

When I last tried the VT220, about 7 years ago, I found that its keyboard had stopped working sometime between the late 90s and then. The symptom was that the four status LEDs would stay lit and the terminal would say "Keyboard error - 4" and that was that.

Seeing as I've not a lot of other machines which need fixing at the moment I brought it and the terminal out of storage to see if I could fix it.

After removing it from its case I set about checking for life around the microcontroller... well there was some and it was communicating with the terminal as I could see serial data going both ways. This was a good sign.

IMG_4913.jpeg

Doing some Googling suggested that the problem may be a stuck key and one blog post suggested that removing the membrane ribbons from their sockets would allow the self-test to pass. So, I did just that and.... four lit LEDs.... and around 8 volts on a load of the connections!

Looking more closely, the membrane ribbons are held against the pcb by steel hoops which go over the top and have individual leaf springs pushing on the ribbon. On one of these connectors there are two extra pads not used by the membrane and one of those was connected to all four LEDs and was powered indirectly from the 12V part of the board! The steel hoop was, of course shorting all the PCB pads together.

Hoping that I'd not fried something I launched into bending the lugs one the three hoops to disconnect them from the PCB. With those gone I could try the board without the keyboard connected... Diagnostics passed. OK, so the PCB is fine... must be the membrane.

I downloaded the DEC maintenance manual for the LK201 keyboard, which thankfully had the matrix layout.

A quick check of the lines on the matrix showed very many shorted connections. Oh...

Anyway, with a great deal of struggling and swearing I managed to clip the membrane ribbons onto the PCB. They had to be mounted by putting the ribbon in the correct location, with the PCB fully fitted to the keyboard back sheet, and then getting the steel hoop over the top, sliding it back until the lugs on the side can go into the tight holes in the PCB. Then flip the whole keyboard over, holding the hoops so that it doesn't move, and then try to force the thick steel lugs over to hold the hoop in place... and do this with all three ribbons, without them twisting to the side or coming out from under the hoops. Nightmare!

With it back together I could get the oscilloscope on the go. That showed that at least 13 keys were stuck as I could see the individual pulses from the scanning on practically every sense line.

Wondering if a bit of hot air may help the membranes relax and the contacts be pulled apart I put the rework station onto 100C and heated the front and rear of the keyboard, which took a while given the large steel plate. I then continuously pounded and mashed the keys. Eventually one by one the number of stuck lines decreased, until just four were left which stubbornly wouldn't free.

That was where I left it last night, thinking it a lost cause.

This morning I decided that as it was a lost cause anyway I may as well do radical and risky things and just see what I could do.

The way the keyboard works is that there are nylon frames into which the keycaps clip. On the bottom of these are leaf springs pressed upon by the ends of the key cap stalks. The springs have a little point which presses through a rubber sheet onto the three layer membrane underneath. This membrane is very similar in construction to the ST's. The frames are held in place by moulded pegs which go through two holes in the springs and then holes in the rubber sheet, membrane and lastly the steel back plate. The pegs are then melted on the back to hold the sandwich together. The only way to get access to the membrane is to cut these melted bits off to free the frame. However, this means that the original method of holding the keyboard together is no-longer available. Completely unmaintainable.

Seeing as this was at the point of "what the heck!" anyway, I decided to cut away the bits of the keyboard with stuck connections so I could take a look at the membrane underneath.

IMG_4911.jpeg

Lifting the rubber sheet I could see what the problem was. At some point the keyboard must have been laying with something reasonably heavy on top for many years. The conductive paint on the two membrane pads which act as the switch had glued themselves together. The only way they separated was when the paint on one side or the other was pulled away from the plastic on the other pad. Thankfully, the areas involve were small so the key switch still operated.

Having freed the last of the stuck pads the keyboard passed the diagnostics and the terminal showed the welcoming "VT220" display.

Now all I had to do was work out how to reattach the frames.

IMG_4910.jpeg

I decided to snip off a fre of the pegs and drill out holes and then use M2 self tapping screws instead of the melted ends. The other pegs would be used for location and to hold the rest of the springs. M1 screws would have been better but M2 were the smallest I had.

IMG_4914.jpeg

After a few false starts I finally got the keyboard back together and working.

IMG_4912.jpeg

It just left firstly putting it into its case and then 3D printing some clips for keycaps where the clips had broken away when removing them.

IMG_4916.jpeg

Anyway, it's back together now and all fixed.

IMG_4915.jpeg

Phew! I dind't think I'd be able to bring this one back from the brink.