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Bungo Pony
December 7th, 2017, 10:33 AM
So it appears that I got my Altair 8800 working (from a completely non-working state), but the problem I'm having is the D0-D7 LEDs are always in the on position. Hard reset works, stepping through the addresses works, but reading and writing to them do nothing to change their state.

I've never repaired anything RAM related, so it's kind of new territory. I've re-seated every chip, swapped the ones that are identical to see if there's any change, but nothing's changed. I replaced a bad voltage regulator, but that's the only thing I've found wrong with the board. Bit 7 on the dip switch doesn't work, but from what I've read, the dip switches are only used for testing the RAM chips themselves.

My next guess is to re-cap the entire thing, although I'm not quite certain on how to read the red capacitors. I'm guessing these are rated at 0.1 uF, but I'd like confirmation on that.

Has anyone re-capped one of these boards and had it work afterwards?

4237642377

glitch
December 7th, 2017, 10:52 AM
Are you sure you're at the right address for the board? Set up what you think is the right address, do an EXAMINE, and probe the output of the address decoder circuit with a logic probe (and, if you don't have a logic probe, get one!). I've got the same SSM 4K board and have been unable to find documentation on it, but it's a pretty straightforward board. Should be pretty easy to find the address compare output and trace it out.

FYI, I generally start testing with either a ROM board or my debug board, which allows setting a known bit pattern on DIP switches. This will help you catch mis-wired front panel cables, bad bus drivers, etc.

Chuck(G)
December 7th, 2017, 11:28 AM
I doubt that those bypass caps are giving you any problems, so I'd skip over that for now.

I don't know where you got your information about the DIP switches, but I seem to recall that on these boards (and the 8K SRAM board), the switches set the base address as well as the "memory protect" state--i.e. when a block of memory is protected, you can't alter the contents--this was useful back in the days before affordable disk storage when most programs were toggled in through the front panel--you didn't want your hard work to go *poof* because of a coding or entry error. I think the remaining DIP switch sets the number of wait sates (memory, especially SRAM, could be pretty slow back in the day).

I don't have the manual for your board, as it precedes the very popular (for SSM, anyway) 8K board.

After verifying the DIP switch settings, i'd verify the output of each of the voltage regulators. I'd also re-seat the socketed interface chips.

Bungo Pony
December 7th, 2017, 03:13 PM
Are you sure you're at the right address for the board? Set up what you think is the right address, do an EXAMINE, and probe the output of the address decoder circuit with a logic probe (and, if you don't have a logic probe, get one!). I've got the same SSM 4K board and have been unable to find documentation on it, but it's a pretty straightforward board. Should be pretty easy to find the address compare output and trace it out.

I had no clue I had to do any of this! I don't even know where to begin! All I did was get the Altair functional (I'm a first time owner).


I don't have the manual for your board, as it precedes the very popular (for SSM, anyway) 8K board.

Although I have the assembly manual and test procedures that originally came with my Altair, I don't have any documentation for the RAM board. I tried looking for some online, but it doesn't seem to exist.


I seem to recall that on these boards (and the 8K SRAM board), the switches set the base address as well as the "memory protect" state

So I have to set up the address for the RAM board with the dip switches? My apologies if I'm not understanding clearly how this all works.

DaveL
December 7th, 2017, 04:57 PM
You should be able to get some documentation here (http://retrotechnology.com/herbs_stuff/s_ssm.html).

Dwight Elvey
December 7th, 2017, 05:15 PM
The switches are likely in sets of 4.
Try putting the sets of 4 in all 4 combinations.
Use address 0 and write a 10101010 pattern.
Another option is to trace the S100 address lines and the wires
to the switches.
Dwight

Moonferret
December 8th, 2017, 12:17 AM
One configuration you could try which I've seen on a couple of older 4K boards is where the 8 switches are configured as two sets of 4. The first four switches selects one of four 16k banks within the 64k address space and then the second set of four switches selects the 4k bank within the selected 16k.

Eg. If this is the only card in the system you would set it to 10001000 (First 4k in the first 16k bank)

Chuck(G)
December 8th, 2017, 08:30 AM
A bit on the switches (https://www.worthpoint.com/worthopedia/s100-solid-state-music-4k-ram-vintage-1834520497\)

I don't see the 4K static RAM board in Herb's Retrotechnology list.

Al Kossow
December 8th, 2017, 10:40 AM
So it appears that I got my Altair 8800 working (from a completely non-working state), but the problem I'm having is the D0-D7 LEDs are always in the on position. Hard reset works, stepping through the addresses works, but reading and writing to them do nothing to change their state.

I've never repaired anything RAM related, so it's kind of new territory. I've re-seated every chip, swapped the ones that are identical to see if there's any change, but nothing's changed. I replaced a bad voltage regulator, but that's the only thing I've found wrong with the board. Bit 7 on the dip switch doesn't work, but from what I've read, the dip switches are only used for testing the RAM chips themselves.

My next guess is to re-cap the entire thing, although I'm not quite certain on how to read the red capacitors. I'm guessing these are rated at 0.1 uF, but I'd like confirmation on that.

Has anyone re-capped one of these boards and had it work afterwards?



this appears to be a SSM MB-2
https://archive.org/stream/TNM_Solid_State_Music_various_boards_1977_20170922 _0031
MB-4 looks similar, and refers to it as an improved MB-2

DaveL
December 8th, 2017, 11:51 AM
A bit on the switches (https://www.worthpoint.com/worthopedia/s100-solid-state-music-4k-ram-vintage-1834520497\)

I don't see the 4K static RAM board in Herb's Retrotechnology list.

I was thinking the MB4 would be the card. Maybe not.

Dwight Elvey
December 8th, 2017, 02:35 PM
this appears to be a SSM MB-2
https://archive.org/stream/TNM_Solid_State_Music_various_boards_1977_20170922 _0031
MB-4 looks similar, and refers to it as an improved MB-2

Are you sure this is the right link?
Dwight

Chuck(G)
December 8th, 2017, 03:43 PM
It's a catalog of SSM offerings, Dwight. The MB-4 is described in there.

Apparently, available as an 8K board with 2Kbitx1 2102-style pinout. But I don't know what IC that would be.

Moonferret
December 8th, 2017, 03:46 PM
It's weird that in the parts list for the MB4 it states that the 4K version is in 32 chips whereas the 8K is 64 chips. In the photo, that board certainly only has 32 sockets

EDIT - Just read, the chips are piggybacked - Probably just 2102's

Chuck(G)
December 8th, 2017, 04:03 PM
Piggybacked? One can only hope that 21L02s were being used. 2102s run pretty warm.

Bungo Pony
December 9th, 2017, 02:01 AM
Thank you everyone for your help, and now I have some things to go on. I'll be ordering a replacement dipswitch since the one on the board isn't very good, and the last switch doesn't work.

This 4k board seems to be a bit of an odd and rare beast. It also has a very mild vibration when it's powered up. I'm only guessing that's normal.

Every version I've seen of this board online has a mod done to it, where the 7 dip switches are replaced with 4, and there's a switch at the top. Two voltage regulators are also removed. There's one on ebay right now:

http://www.ebay.ca/itm/Solid-State-Music-4K-Static-RAM-RARE-S-100-board-ships-worldwide/152778302533?hash=item23924be445:g:inMAAOSwPhdVCdn 9

8008guy
December 10th, 2017, 05:51 AM
This 4k board seems to be a bit of an odd and rare beast. It also has a very mild vibration when it's powered up. I'm only guessing that's normal.



Vibration?

I've had a lot of 2102 memory boards over time, nothing with vibration.

DaveL
December 10th, 2017, 04:01 PM
... It also has a very mild vibration when it's powered up. I'm only guessing that's normal. ...


Regulator(s) oscillating/ringing?

glitch
December 11th, 2017, 05:04 AM
Every version I've seen of this board online has a mod done to it, where the 7 dip switches are replaced with 4, and there's a switch at the top. Two voltage regulators are also removed. There's one on ebay right now:

http://www.ebay.ca/itm/Solid-State-Music-4K-Static-RAM-RARE-S-100-board-ships-worldwide/152778302533?hash=item23924be445:g:inMAAOSwPhdVCdn 9

Mine's not cut up like that. I'll see if I can dig it out later today, I may have notes on the DIP switch settings as well. I know I had it working in the past few years -- I like SSM stuff a lot, but 4K is not a super useful size!

Chuck(G)
December 11th, 2017, 05:56 AM
If anyone's interested, I note that Anchor Electronics is still offering the SSM 64KB and 32KB PCB blanks for sale:

Product page here (http://anchor-electronics.com/product-category/s-100-bus/)

Dwight Elvey
December 11th, 2017, 09:01 AM
Thank you everyone for your help, and now I have some things to go on. I'll be ordering a replacement dipswitch since the one on the board isn't very good, and the last switch doesn't work.

This 4k board seems to be a bit of an odd and rare beast. It also has a very mild vibration when it's powered up. I'm only guessing that's normal.

Every version I've seen of this board online has a mod done to it, where the 7 dip switches are replaced with 4, and there's a switch at the top. Two voltage regulators are also removed. There's one on ebay right now:

http://www.ebay.ca/itm/Solid-State-Music-4K-Static-RAM-RARE-S-100-board-ships-worldwide/152778302533?hash=item23924be445:g:inMAAOSwPhdVCdn 9

Depending on where in the cycle the power switch closes, the power transformer can make a noticeable thump. This is
not all that unusual.
Dwight

glitch
December 11th, 2017, 09:48 AM
If anyone's interested, I note that Anchor Electronics is still offering the SSM 64KB and 32KB PCB blanks for sale:

Product page here (http://anchor-electronics.com/product-category/s-100-bus/)

These are California Computer Systems boards, it looks like. They do have a single SSM VDB-1 video board, but the listing says it's probably a bad etch.

Chuck(G)
December 11th, 2017, 10:11 AM
You're correct--and that explains the green solder mask. :) I was going based on the original owner of Anchor.

Still, not a bad deal...

Dwight Elvey
December 11th, 2017, 12:25 PM
If you can give us a closer picture of the top of the board where we can determine the values
of the ICs and see the traces to the edge connector as well as a similar picture of the traces on that
same area of the bottom of the board, we can likely work out the switch positions.
The picture you have is not of enough quality to determine the ICs and there is no bottom traces.
The 4K on the ebay is a different version and only has a 4 position switch.
Dwight

Bungo Pony
December 17th, 2017, 02:55 AM
If you can give us a closer picture of the top of the board where we can determine the values
of the ICs and see the traces to the edge connector as well as a similar picture of the traces on that
same area of the bottom of the board, we can likely work out the switch positions.


No problem. Here's the top:

http://www.files.classicalgasemissions.com/imgs/ssmram.jpg

Here's the bottom:

http://www.files.classicalgasemissions.com/imgs/ssmram2.jpg

glitch
December 17th, 2017, 01:09 PM
Dug mine out today, and even desoldered the DIP switch to verify settings! Here we go:

Switches 1, 2: wait state control

Switches 1 and 2 will ground out the *CLR lines on two elements of a 74LS74 dual flip-flop. It looks like the intention was to allow one or two wait states to be inserted, but my board only inserts wait states of both switches are OPEN. I haven't 'scoped it to figure out how many wait states are inserted, it's not all that relevant on an 8080 system.

Switch 3: not connected (desoldered switch pack to verify)

Switch 4 - 7: board address control

These are inverted sense; that is, a closed switch is logic 0 for the address comparator. To set the board's starting address to 0x0000, close/turn on switches 4, 5, 6, 7. They correspond to bits as follows:

4: address bit 15
5: address bit 14
6: address bit 13
7: address bit 12

Works fine with a front panel, of course. There does not seem to be memory protect support, so nothing to worry about there. For basic testing, set 1,2 to OFF and the rest to ON. Set up address 0x0000 and EXAMINE. Try and deposit all 0s, then all 1s. If you can't make any bits change, something's wrong. If you get a bit that won't change, there's a bad SRAM at that location. If your address lights don't show as all off when you do the EXAMINE then you've got bigger problems in your system.

If you can't make any bits change, hook up the logic probe and test pin 8 of the DM8131 address comparator (immediately below the switch pack). It should be low. If it's not, you've either got a bad comparator, bad comparator socket, broken switch pack, broken pull-up resistor(s), or there's something wrong with your Altair's CPU board/backplane.

Dwight Elvey
December 18th, 2017, 03:11 PM
I'm looking at the picture and it looks to me that the DM3181 may be upside down. I'm not saying to reverse it until we know what direction it is. These parts are not forgiving about having VCC and GND mixed. If it was powered up upside down, it is likely not in too good a shape.
A closer picture might help me determine if it is upside down.
DM3181s are a little hard to find.
Dwight

Chuck(G)
December 18th, 2017, 03:53 PM
I think it's correct--from the rear view, pins 1,2, 7,8 and 14,15 are all grounded, with Vcc going to pin 16.

That translates to B1,T1, B6,T6 and STROBE* all being low. That is, the DM8131 is being used as a simple non-strobed quad comparator. Probably a matter of using what was on hand, instead of the more logical choice of a 7485.

Dwight Elvey
December 18th, 2017, 04:02 PM
Your right Chuck. I got confused by the regulator pins. I can see now it looks to be in places correctly. I hate when they make boards with pin 1 oriented every which way.
Dwight

Chuck(G)
December 18th, 2017, 04:15 PM
Saves on copper, Dwight! :)

(I'm with you on that one! Confusing as heck.)

glitch
December 18th, 2017, 04:28 PM
Yeah, it's correct, I've got a working one in front of me to verify with. I'm guessing he just didn't have the thing addressed properly (original pics show it at the top of address space, rather than bottom). Or the Altair has bigger issues.

I also hate boards with pin 1 pointing everywhere. I make an effort to design all of mine so that pin one points to whatever is reasonably the top of the card. Usually that equates to, "away from the bus connector."

Dwight Elvey
December 19th, 2017, 02:41 PM
After I thought about it, I realize I've done it recently. On my 6530 to 6532 adapter, I have a PAL and a EEPROM tucked under the 6532 but pin1 down, compared to pin1 up on the 6532. The power pins on the 6530 and 6532 on the wrong ends of the part. I was really crammed for routing space and saved an additional X of traces by flipping them. I still don't like it in general. I'd have had more space it the idiots at MOS had made the pinout of the 6530 and 6532 more compatible. Only 10 pins out of 40 are matching locations and two of them are power and ground.
Dwight

Dwight Elvey
December 20th, 2017, 09:53 AM
Back on subject:
I'm curious as to what progress is being made on the RAM card?
Dwight

Dwight Elvey
December 20th, 2017, 12:11 PM
Some more info that might be useful once you can actually see data from the RAM.
The columns left to right from the top of the board are:

D2 D3 D7 D1 D0 D4 D5 D6

Why they couldn't get these in the right order I'll never know.

If I traced the wires right, the top row is the lowest address and the bottom row it the highest address of the selected 4K.
The RAMs look to be typical 2102 type.
Dwight

Bungo Pony
December 24th, 2017, 05:47 AM
Back on subject:
I'm curious as to what progress is being made on the RAM card?
Dwight

I'm waiting for a replacement dip switch to arrive in the mail because the one on the board isn't working properly. I'll update once it comes and I solder it in.

glitch
December 24th, 2017, 09:25 AM
If you run it with the DIP switch completely out (same thing as all switches open), it'll show up on the 4K page at 0xF000 and should otherwise work fine. That's assuming that both the RAM board and the rest of the Altair are fine :)

Bungo Pony
January 13th, 2018, 06:31 AM
The dip switch arrived, and I soldered it into place.




Switches 1, 2: wait state control

Switches 1 and 2 will ground out the *CLR lines on two elements of a 74LS74 dual flip-flop. It looks like the intention was to allow one or two wait states to be inserted, but my board only inserts wait states of both switches are OPEN. I haven't 'scoped it to figure out how many wait states are inserted, it's not all that relevant on an 8080 system.

Switch 3: not connected (desoldered switch pack to verify)

Switch 4 - 7: board address control

These are inverted sense; that is, a closed switch is logic 0 for the address comparator. To set the board's starting address to 0x0000, close/turn on switches 4, 5, 6, 7. They correspond to bits as follows:

4: address bit 15
5: address bit 14
6: address bit 13
7: address bit 12

Works fine with a front panel, of course. There does not seem to be memory protect support, so nothing to worry about there. For basic testing, set 1,2 to OFF and the rest to ON. Set up address 0x0000 and EXAMINE. Try and deposit all 0s, then all 1s. If you can't make any bits change, something's wrong. If you get a bit that won't change, there's a bad SRAM at that location. If your address lights don't show as all off when you do the EXAMINE then you've got bigger problems in your system.



I'm happy to say that I've been able to deposit and examine the bits properly... until I hit #31. I ended up swapping some RAM chips around and isolated a bad one. I shall be working on seeking one (maybe two or three) to remedy the problem.

I'm absolutely thrilled I've been able to get this Altair to the point it's at. It was completely non-working when I got it, had leaky caps on the supply, broken wires, and a few blown parts. It's now almost 100% functional!

Thank you everyone for your input and help. It was very much appreciated.

glitch
January 13th, 2018, 07:43 AM
Glad to help! I've got 2102s if you need them, but I suspect you can find someone in Canada and avoid having to pay high shipping for just a few ICs.

Bungo Pony
January 16th, 2018, 01:44 AM
Glad to help! I've got 2102s if you need them, but I suspect you can find someone in Canada and avoid having to pay high shipping for just a few ICs.

I've got some on the way which have the gold tops on them. They weren't highly expensive, and I paid just a little bit more for the gold tops so I can have a pretty RAM board :D

They should be here sometime this week. I've also been recording video of all the repairs I've done to this thing.

glitch
January 16th, 2018, 09:06 AM
Excellent, look forward to seeing them!