IMSAI 8080 CP/M 2.2 - Diagnostic Software?

[tma]

Greetings,

Although my IMSAI still boots CP/M 2.2 OK and will list directories to the console I would like to increase my confidence level regarding the hardware. I would like to scan the memory for errors, do write/read tests to the drives and possibly other tests based on recommendations. I notice that with some of my near 4 decade old diskettes I get bad sector messages. Some will boot OK and others fail. I suspect the diskettes have probably deteriorated. They have been exposed to the magnetic environment over the years.

Any suggestions regarding diagnostic software to run and possibly other tests?

Best Regards,
tma

 

[glitch]

There are a number of system-nonspecific memory tests that will work for testing your memory. I use the built-in tests in some of the various ROM monitors I have for most board testing (Dajen SCI monitor, Vector Graphic monitor, and Cromemco monitor, for example).

As to diskettes, anything mechanical will wear, my personal policy is image everything as soon as possible. What disk subsystem are you using? There may be tools out there for what you've got. With the age of original media, it's just a matter of time before you lose something irreplaceable or have to write something over, if you're not backing up to more stable media (i.e. a modern computer, which is then itself backed up).

 

[MicrocomputerSolutions]

If I were you, I'd start with a head cleaning for the floppy drives, before I made any conclusions about the health of the magnetic media. Through normal use, the oxide get worn off the floppies, and often deposits on the head/s, causing errors as the coating of debris thickens. I recommend using a q-tip and alcohol, instead of cleaning disk kits, as I would be worried about the cleaning pads causing accelerated wear to the head load pad on single-sided drives.

Most people never check or replace them, but headload pads were never designed to last forever. The odds are that yours are in need of replacement after all this time. Worn headload pads can result in low head output and read/write errors. Of course there haven't been any replacement available for years, so if yours are worn, you may need to find an alternative source for the material and make your own.

Your single-sided floppy drives are probably long overdue for a checkup/alignment. I used to recommend an alignment once a year to have the heads cleaned, headload pads replaced, and alignment checked/adjusted. This can be the cause for the errors that you have been noticing. The more reliable brands of double-sided drives will go much longer between alignments because they don't have headload pads to wear-out (and replace).

I have hundreds of 8" disks that are stored for the most part in plastic disk cases in the closet when they are not being used. The lower quality ones were thrown away years ago as they developed problems, but the bulk of my floppies have never given me any trouble and are over 30 years old now. I don't think you necessarily have to worry about losing disks, programs/data. Just make sure that you keep at least two of every recorded disk, and only use quality floppies. Most of my floppy collection consists of Dysans (from before Verbatim took over), but I also have significant numbers of BASF, Elephant, Verbatim, TDK, Scotch/3M, and other floppies.

I use the diagnostic routines embedded in my SD Systems board set SD Monitor Rom, and SD Systems Versafloppy II Diagnostic Rom on my SD Systems board set.

On my Compupro System, I use a set of diagnostic programs that was included by Compupro with the CDOS OS disk set. Some of the included diagnostics are programs written by another company (like the memory tester) while other programs were written by Compupro to test specific Compupro components. There are routines for testing the memory, main processor, math co-processor, MDrive/H board, Interupt and interval timers, slave processors, the hard and floppy controllers, and the I/O Ports.

 

[tma]

Greetings,

Many thanks for the great support info!

I need to look into what is involved to check the tracking alignment of the drives. I noticed an inconsistency between them whilst running the SD Systems vdiag.com read test. The vdiag utility has a number of good diagnostics for thoroughly testing the drives. I do have the drive service manuals but I don't have an alignment disk. I am on the learning curve here as I have never attempted to aligned a drive before.

I wonder if alignment disks are still available or if one could possibly use a know good disk? I suspect an alignment disk probably has a special bit pattern to make it easier to view the data with a scope.

I do have some software distribution diskettes that have never been disturbed. I wonder if it might be possible to use one of them for the alignment reference?

Best Regards,
tma

 

[MicrocomputerSolutions]

There is a company that still manufacturers alignment disks. I don't know how much they cost as I am still operating using 15-20 ( as I wear out, or the disks get damaged, I make a note of the damage, and continue to use the undamaged parts of alignment disks) alignment disks that I have remaining from the ones that I bought back in the 80s and 90s. They cost about $100 each back then.

To use an analog alignment disk, you need a drive exerciser, or a routine to command the drive to move to specific tracks on the alignment disk so you can observe waveforms with a 100mhz (or better) dual trace oscilloscope (Tektronix 465 being the classical standard for drive alignment) or a dedicated drive tester (mine costed about $1000-$1500 back around 1983). And the alignment disk.

I've been using a dedicated drive tester to read the drives, and a drive exerciser from another company to control drives since the 1980s. The companies that made the these tools have been out of business for decades now. And I'm worried about how long they are going to keep operating. I don't have circuit diagrams for either tool, and the drive tester died twice in the past, and had to be sent to the Manufacturer at the time for repairs. In anticipation of the final death of this hard working equipment, I purchased a used 150mhz Tektronix 2445 scope (and a donor 2445 scope to use for parts) and am looking for replacements/spares for the drive tester and exerciser.

Aligning drives using an oscilloscope is many times slower than using the dedicated drive tester, but may be necessary in the future if I'm going to continue servicing floppy drives. In a production environment, I found it much faster to use the dedicated drive testing equipment than the oscilloscope that I learned to do the work on. I never used a scope before for repairing floppy drive logic boards, but I've accumulate a pile of dead logic boards over the years that I was not able to fix using a DMM and logic probe (which is all I've needed for most repairs). I'm going to use the scope to hopefully track down the problems on the boards I could not fix before (about 15-20 logic boards accumulated).

With your previous experience, I'd think you'd be able to write the drive control program and use your computer to control the floppy drive. If you have a good 100 mhz dual trace scope, all you would need to align/verify your drives are in alignment (or to be able to adjust the alignment) is a analog alignment disk. I haven't bought any lately (as I wrote previously) but I've been to the manufacturer's website, and seem to remember a price somewhere between $70-$100 for a 8" analog alignment disk. I charge about $100 to align a 8" single-side drive, or $150 for a simple repair and alignment with an extra fee of between $100-$200 to repair, exchange or out-right replace a defective logic board. If you can do your own alignments for the cost of an alignment disk, that would be a good investment.

 

[tma]

Greetings,

Again many thanks for your great support! I happen to own a Tektronix 466 and also a big quad channel 100 MHz mainframe Tektronix scope on a cart (forget the plug in models but a 7000 series frame as I recall). I still need to check out the pads and clean the heads as you mentioned in your earlier post. My available time yesterday was used up re-learning how the test the drives with the diagnostics (been about 4 decades since I have been there thus it is like starting over). Nice that you have the specialized tools for doing the track alignment job. A pitfall with owning such nice instrumentation from the past is the servicing. Fortunately with the main line test gear one can usually find a service manual. But even with the documentation and successful trouble shooting the parts can become very hard to find. It took me years to find a Tektronix IC for the sweep module I needed for one of my older scopes. Back then (and no doubt still today) instrumentation manufactures used unique components which of course become manufacture discontinued.

For logic circuit analysis I bought a USBee logic analyzer pod a few years ago. What a wonderful tool for analyzing the happenings on a bus. One can trigger the capture and then scroll back to compare the transition timing on multiple lines. It even will decode ASCII from serial data. With hindsight I wish I would have bought one of those analyzer pods much sooner. In the deeper past I have spend days trying to track down problems with a storage scope that could have been located within a few hours with the multi-line input logic analyzer USB pod.

Best Regards,
tma

There is a company that still manufacturers alignment disks. I don't know how much they cost as I am still operating using 15-20 ( as I wear out, or the disks get damaged, I make a note of the damage, and continue to use the undamaged parts of alignment disks) alignment disks that I have remaining from the ones that I bought back in the 80s and 90s. They cost about $100 each back then.

To use an analog alignment disk, you need a drive exerciser, or a routine to command the drive to move to specific tracks on the alignment disk so you can observe waveforms with a 100mhz (or better) dual trace oscilloscope (Tektronix 465 being the classical standard for drive alignment) or a dedicated drive tester (mine costed about $1000-$1500 back around 1983). And the alignment disk.

I've been using a dedicated drive tester to read the drives, and a drive exerciser from another company to control drives since the 1980s. The companies that made the these tools have been out of business for decades now. And I'm worried about how long they are going to keep operating. I don't have circuit diagrams for either tool, and the drive tester died twice in the past, and had to be sent to the Manufacturer at the time for repairs. In anticipation of the final death of this hard working equipment, I purchased a used 150mhz Tektronix 2445 scope (and a donor 2445 scope to use for parts) and am looking for replacements/spares for the drive tester and exerciser.

Aligning drives using an oscilloscope is many times slower than using the dedicated drive tester, but may be necessary in the future if I'm going to continue servicing floppy drives. In a production environment, I found it much faster to use the dedicated drive testing equipment than the oscilloscope that I learned to do the work on. I never used a scope before for repairing floppy drive logic boards, but I've accumulate a pile of dead logic boards over the years that I was not able to fix using a DMM and logic probe (which is all I've needed for most repairs). I'm going to use the scope to hopefully track down the problems on the boards I could not fix before (about 15-20 logic boards accumulated).

With your previous experience, I'd think you'd be able to write the drive control program and use your computer to control the floppy drive. If you have a good 100 mhz dual trace scope, all you would need to align/verify your drives are in alignment (or to be able to adjust the alignment) is a analog alignment disk. I haven't bought any lately (as I wrote previously) but I've been to the manufacturer's website, and seem to remember a price somewhere between $70-$100 for a 8" analog alignment disk. I charge about $100 to align a 8" single-side drive, or $150 for a simple repair and alignment with an extra fee of between $100-$200 to repair, exchange or out-right replace a defective logic board. If you can do your own alignments for the cost of an alignment disk, that would be a good investment.

 

[MicrocomputerSolutions]

The nice thing about the Internet is the ease of which you can find SIGs (special interest groups) that discuss what you're interested in. I 'm not sure I would have started to tackle the restoration of a Tektronix 2445 scope if I wasn't able to find the service and operations manuals online, and people with the same scopes who are willing to help with experienced advice.

Tektronix designed a bunch of hybrid ICs into the 2200 and 2400 series scopes that they manufactured in their own chip factory. Years ago they sold the IC manufacturing facility and lost the ability to build replacement hybrids (new owner of the chip factory declined to keep making these specific hybrids for Tektronix). Owners of the scopes love them, and have had to resort to buying donor scopes for parts to keep their scopes in operation when a hybrid fails, since Tektronix has ended all support for this line of scopes, and there are no more new spare hybrids to be had at any price.

I've read that the weak point in the Tektronix 4XX series of scopes is/are some tunnel diodes that are no-longer available. Someone mentioned using some surplus Russian made parts as a substitute.

 

[tma]

I bought my 466 before the days of the Internet. It turned out to have an intermittent issue. I somehow managed to get a copy of the service manual for it. I eventually found that there was an intermittent 3 terminal regulator. I was lucky as it was a standard production part and easy to get. My 466 has now served me for a couple of decades (I am touching wood as I type this). Unfortunately the storage screen had become burnt a little before I got it. But it is still useble.

The nice thing about the Internet is the ease of which you can find SIGs (special interest groups) that discuss what you're interested in. I 'm not sure I would have started to tackle the restoration of a Tektronix 2445 scope if I wasn't able to find the service and operations manuals online, and people with the same scopes who are willing to help with experienced advice.

Tektronix designed a bunch of hybrid ICs into the 2200 and 2400 series scopes that they manufactured in their own chip factory. Years ago they sold the IC manufacturing facility and lost the ability to build replacement hybrids (new owner of the chip factory declined to keep making these specific hybrids for Tektronix). Owners of the scopes love them, and have had to resort to buying donor scopes for parts to keep their scopes in operation when a hybrid fails, since Tektronix has ended all support for this line of scopes, and there are no more new spare hybrids to be had at any price.

I've read that the weak point in the Tektronix 4XX series of scopes is/are some tunnel diodes that are no-longer available. Someone mentioned using some surplus Russian made parts as a substitute.