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Processor Technology SOL 20 at the RICM

m_thompson

m_thompson

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Location
Rhode Island, USA
Because of our recent success with reviving two Altairs we decided to try another S-100 system. We moved a Processor Technology SOL 20 from the warehouse to the Lab space, cleaned and inspected the inside of the case, reformed the electrolytic capacitors in the power supply. We disconnected the power supply from the motherboard and the S-100 expansion chassis, and measured the power supply voltages. The +5V and the +/-12V for the motherboard were OK, The +/-18 for the S-100 bus was OK, but the +7V for the S-100 bus was dead. Since it didn't have any S-100 boards installed we reconnected the power supply harnesses and powered it on. We didn't see any smoke, flames, or sparks, and it didn't blow the fuse, so I would call that a success.

We need to make a video cable so at this point we don't know how much of the system is working. We tried a few keys on the keyboard and noticed that shift-lock didn't work. We disassembled the keyboard and found that all of the foam pads for the keys were really degraded. Looks like we will need to either buy a set of pads, or make them ourselves.
 
m_thompson said:
We disassembled the keyboard and found that all of the foam pads for the keys were really degraded. Looks like we will need to either buy a set of pads, or make them ourselves.
Click to expand...

I installed a set of pads from TexElec in my Sol 20, but hardly any of them worked. I replaced them with a set of pads from a Sun Type 4 keyboard, and everything worked. YMMV.
 
mloewen said:
I installed a set of pads from TexElec in my Sol 20, but hardly any of them worked. I replaced them with a set of pads from a Sun Type 4 keyboard, and everything worked. YMMV.
Click to expand...

We ordered a new and improved set of pads from TexElec. We will report how they worked.
 
mloewen said:
I installed a set of pads from TexElec in my Sol 20, but hardly any of them worked. I replaced them with a set of pads from a Sun Type 4 keyboard, and everything worked. YMMV.
Click to expand...

The reason why the initial set of pads from TexElec did not work for all keys is explained in this detailed analysis of the SOL-20's Keyboard:

http://worldphaco.com/uploads/HARDWARE_DIAGNOSTIC_TOOL_FOR_THE_SOL.pdf

I did not get to try their current 2nd generation pads because I moved to the ones harvested from the SUN-4 keyboard for my own SOL-20.
 
We did a little more work on the SOL yesterday. All of the old pads in the keyboard have been removed. We pulled a Wang keyboard from the warehouse so we can harvest the pads and put them in the SOL keyboard.

We connected the system to a monitor and powered it on. The screen was blank except for the bottom two rows that contain alternating number 9 and a box if the display control characters switch is turned on.

We looked at the signals on the video RAM and the system RAM. Both have reasonable signals so it looks like the video circuitry is working and the 8080 is alive.

The legs on the ICs are covered with black corrosion. We started removing the ICs, cleaning the legs with with DeoxIT and a brass brush, put a little DeoxIT on the socket contacts, and reinstalled the ICs. We are about half way through this process and should finish it next week.
 
m_thompson said:
We did a little more work on the SOL yesterday. All of the old pads in the keyboard have been removed. We pulled a Wang keyboard from the warehouse so we can harvest the pads and put them in the SOL keyboard.

We connected the system to a monitor and powered it on. The screen was blank except for the bottom two rows that contain alternating number 9 and a box if the display control characters switch is turned on.

We looked at the signals on the video RAM and the system RAM. Both have reasonable signals so it looks like the video circuitry is working and the 8080 is alive.

The legs on the ICs are covered with black corrosion. We started removing the ICs, cleaning the legs with with DeoxIT and a brass brush, put a little DeoxIT on the socket contacts, and reinstalled the ICs. We are about half way through this process and should finish it next week.
Click to expand...

The pins that go black are usually the TI type which are silver plated steel.

Generally for the SOL-20 they were very big on the TI sockets that grab the pins from side to side (rather than across the flat). If you inspect the IC pins under magnification you will find oxide deposits where are a grey or dark line is on the surface (oxides are insulators) this must be removed for a reliable connection. It is caused by electrochemical effects of the dissimilar metals of the claw and IC pin and its plating. Folding over a strip of 1200 or 2000 grade paper works well for cleaning up the pins and of course, if its a TI socket, the pin sides cannot be neglected as this is where the contact is made. I then wash with contact cleaner, and coat the pins with Inox mx-3. I also now use Inox mx-3 to lubricate the sockets. It is superior to any other product (including deoxit) for lubrication & protection of IC socket pins.

Also, the claws in those dreaded TI sockets are very easily damaged by rough IC insertion, especially if the space between the two rows of the IC pins was not pre-formed to fit the socket openings. I would suggest soldering a pin from a defunct IC to a small wire handle and insert it into each IC socket hole to feel the claw tension. Many in my computer were damaged, had little or no tension and intermittent connections. With these TI sockets you can lift the plastic shroud off to get at single claws for replacement or repair, which is better and less stress on the pcb than having to replace the whole socket
 
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