View Full Version : Altos 5-5AD OEM "Dimension Five"

January 22nd, 2008, 11:55 AM
This is an interesting bird, an OEM Altos re-packaged as a Dimension Five by Safeguard Computer Systems.

For about 3 hours in 2005 I could use the system, loaded with MP/M...but then it died.

For a while if standing on one leg and singing "Daisy" I could coax this to the screen:


..."Self test running"...

..."Booting from hard disk"...

..."Hard disk read error status 07 (or 08 or 30)

2008: I thought I'd revisit the system and attempt to replace the ST-506 drive with a new one. Now I can't even get *anything* to the screen. The Wyse monitor I am using seems fine.

Here are some pics:

January 22nd, 2008, 03:19 PM
Hi Bill,
That is a nice system. I think its time to break out the oscilloscope, logic probe, and VOM and go finding the broken parts. Do you have schematics?

I'd start with the power supply and then check the processor signals. It looks like everything is socketed so finding the problem shouldn't be too awful at least to get it to start the monitor again.

Good luck! Thanks!

Andrew Lynch

January 22nd, 2008, 04:57 PM
I have no schematic, at least not yet.

January 22nd, 2008, 05:45 PM
Well even without the schematics you can still do some troubleshooting. Check the PS and CPU states. Also get the data sheets for all the chips and do local checks. Who knows, you might get lucky.

Good luck! Thanks!

Andrew Lynch

January 22nd, 2008, 06:51 PM

If that unit was sent to me for repair, because it's all socketed, the first thing i would do would be the same thing I would do with any early Apple computer.

Having it all socketed is a blessing (easy to replace chips) and a curse (dirt and corrosion can stop the computer dead).

I'd get a can of component cleaner (the non-lubricating kind), remove each chip from it's socket, one at a time, hose down the socket and re-install the chip. Repeat until all sockets have been cleaned.

Then I'd do the same for any power connectors and inter-connect cables.

THEN I'd start looking for damaged components. (of course I'd check the TTL, CMOS and RAM chips because I have a chip tester as I was cleaning the sockets)

In my experience, I'd say about 75% of the time, with older computers, it's a socketed chip problem that is causing the fault.

January 23rd, 2008, 02:45 AM
Hi Richard!

I agree. One of the first steps I do when trying to fix an old machine is remove, clean, and replace all the socketed ICs. I use a wire brush to clear off the corrosion. I have found that doing one chip at a time is best since it reduces the chances of taking out too many and getting confused as to where they go back.

Make backups of the ROMs while you are pulling them out because sometimes they go bad. They'll work on the programmer but fail in the circuit.

I am planning on getting a TOP 2049 IC tester one of these days to check 74LSxxx type chips.

Richard, what IC tester do you use/recommend? Thanks!

Andrew Lynch

January 23rd, 2008, 06:31 AM
Well, I don't know what's out there at the moment and, since I only have had 2, I can only tell you about them.

The first one was Sunshine Company IC Tester that went into an Apple ][ (slot 5) as either a card or a circuit board with a cable that attached to the card and did a good job of testing 74xxxx, 4xxx and 45xx chips and could even tell the difference between chip types (S, LS, H, C etc.), but was slow and, of course, required a computer, monitor and floppy drive, so, you brought the chips to it. I sold it off for an obscene amount a couple of years ago after using it for 20 years or so.

The one I have now is old too, but has an LCD screen, runs off batteries or a wall-wart, and is a MOD-HIC model something or another (it's in my refurb lab and if I ran up there to get it, this thing would time out). It does 74, 40, 45 and any type of DIP RAM above 16K x 1 (I'd love to get something that checked 16K RAMs) and cost me 50 bucks.

It will also suggest other chips that can be substituted for the chip under test and, someday, I'll make a chart of what you can plug in if you don't have the actual chip you need.

I can't justify getting a linear tester though and just find something that has that chip in it to test the target chip.

January 23rd, 2008, 08:23 AM
First of all, I am more of a programmer than a hardware tech (at the component level), and I appreciate your advice. I don't have all of the tools/equipment I need to do what you're suggesting, but I have a friend or two that does in my area. I will see if I can get some help. I keep working at it...and I am patient.

When I power on the system, sometimes it makes it as far as spinning the disk drive, sometimes the hard drive has a "bright" light, sometimes "dim"....rarely if ever is there screen output (or just a "~" or a "p" or something). I have re-seated all of the chips, but that did not do much. I noticed that if I put a finger on the Z80 PIO chip I could get the drive to spin (sometimes). I am sometimes able to activate the reset button and cause the drive to "pink!" once.

Overall the board and machine are in great shape, no visible corrosion.

Fortunately I know someone who used to service Altos machines, I plan to work with him over the next few weeks to try to restore. I will keep you posted.

After the board problems are resolved, I bet I will have to rebuild the OS and replace the hard drive. Fortunately I have a spare (NOS) ST 506.


January 23rd, 2008, 08:25 PM
I'd guess that pressing down on the PIO and getting a reaction is a sign of a cracked solder joint on one of the socket pins. Reflowing (and adding some solder) to all the solder connections on that socket should get you somewhere.

A trick I use when working on socketed boards is to get a sheet of tinfoil twice the size of the board, fold it down to size, put it on some rigid foam, place the logic board on the tinfoil and push it down so the pins puncture the tinfoil and attach one lead of an ohmmeter to the tinfoil.

With the other lead, I go up and down the rows of sockets (you can leave the chips in) checking for 0 ohms. This allows me to quicky test all the sockets on the board for bad chip contact because of corrosion and bad solder joints on the socket to board connections. If you get zero ohms on a medium range, that socket connector is good.

February 3rd, 2008, 06:32 AM
I put up a post on my site, with repair notes. The board is now functional.

I have not yet been able to create a boot disk for the Altos, but I have only spent an hour on it so far. I am attempting to make a boot disk with a Compaq Deskpro 386 that has a high density 5 1/4" drive (and a 3.5HD too). I have been able to get the disk to be recognized, but I am getting an error "10" when attempting to read the disk and boot on the Altos. I will keep working at it.

FOLLOW UP - I was able to make an MP/M boot disk v 2.14. Thanks Dave Dunfield and his ImageDisk!


February 3rd, 2008, 09:37 AM
Follow up to follow up...I was able to boot by floppy to both MP/M and CP/M, and through these regain access to the hard drive without replacing it (drive C). My guess is that when the system originally farted out, it chewed up a little of the file table making it loose it's ability to read track 0. I should be able to clean it up and boot without disk soon.