Signature analyzer would be much more useful than ordinary logic analyzer. I have few logic analyzer including TLA715. I'm always doing everything not to start that monster but rather use handy DSlogic or Salaae Logic 16 (clone) - rarely you need to monitor all the buses in the serviced equipment. Buy good logic probe and logic pulser. Old HP current tracer and logic clip are also not much expensive but very useful. Let TLA715 rest
I started writing a more detailed answer but better descriptions have been written here in the past by more knowledgable people than me. Hunt them down ! Tggzzz is one of them
A Tektronix TLA715 is available locally and I am considering this unit but I basically know nothing when it comes to the probes and adapters I need. It has two of the TLA7N4 (2GHz timing, 64k) modules installed and comes with several of the P6434 probes. Of course these probes are the ones with the Mictor connector and are of no use to me unless I buy or make a Mictor to 2.54mm adapter. I need help determining which probes would be most suitable for my application and I have allocated several hundred dollars for obtaining these probes. According to the pdf, "Tektronix P6400 P6800 P6900 Logic Analyzer Probes" from https://w140.com/tekwiki/wiki/P6434, it looks like most of the probes are compatible with TTL & CMOS levels. I need some sort of flying lead that can be attached to the pins of chips. I have made a little DIP-14/16 breakout PCB with 2.54mm pin headers that I can attach a probe to as well. The P6417 and P6418 appear to be something I can use but I would like to confirm.
And I wish I could afford the HP 547A current tracer mentioned earlier - its amazing that something like that isn’t available today at some affordable price. There must be a reason those things go for $500+ in good condition…
There are lots of options in terms of digital and analogue capture. Get the deepest memory you can afford but be aware you'll sometimes limit the capture to keep the display time down. On these parallel bus processors you'll be using it in state mode though, which is far more efficient for memory use.
There are lots of options in terms of digital and analogue capture. Get the deepest memory you can afford but be aware you'll sometimes limit the capture to keep the display time down. On these parallel bus processors you'll be using it in state mode though, which is far more efficient for memory use.
Memory efficiency is relatively unimportant, especially now memory is so cheap.
What is important is being able to ignore rubbish, so you can concentrate on what is important. That's why state-based arm/trigger/filter is so important: it saves your time. If you don't capture the crap, there's nothing to ignore.
Alternatively: good luck finding the "wrong" bit in 10MS of 32 bit captures.
But if you know what makes it “wrong”, you could always filter out the noise.
If you don’t know what makes it “wrong”, you can’t set up a trigger to begin with.
And sure - I’d take a hardware trigger over not, all other things being equal.
There are lots of options in terms of digital and analogue capture. Get the deepest memory you can afford but be aware you'll sometimes limit the capture to keep the display time down. On these parallel bus processors you'll be using it in state mode though, which is far more efficient for memory use.
Memory efficiency is relatively unimportant, especially now memory is so cheap.
What is important is being able to ignore rubbish, so you can concentrate on what is important. That's why state-based arm/trigger/filter is so important: it saves your time. If you don't capture the crap, there's nothing to ignore.
Alternatively: good luck finding the "wrong" bit in 10MS of 32 bit captures.OTOH: if you don't know what to look for, doing offline analyses on a long capture using advanced search methods (which modern logic analysers do provide) is way more efficient compared to doing lots of captures while trying to kind of narrow down the correct trigger condition. On top of that, a long capture also allows to do other analysis / sanity checks on the data being captured which is simply impossible to do with limited memory depth. Quite often you can find interesting information that way you would have missed otherwise.
The low end modem LAs have very restricted functionality w.r.t. filtering and triggering. Decent modern LAs are fine, as are old LAs from that period, e.g. >HP163x.
The low end modem LAs have very restricted functionality w.r.t. filtering and triggering. Decent modern LAs are fine, as are old LAs from that period, e.g. >HP163x.That would seem to rule out the LA features included in entry level oscilloscopes…. You’re definitely going to need a good dedicated device for this kind of analysis.
Memory efficiency is relatively unimportant, especially now memory is so cheap.
What is important is being able to ignore rubbish, so you can concentrate on what is important. That's why state-based arm/trigger/filter is so important: it saves your time. If you don't capture the crap, there's nothing to ignore.
Alternatively: good luck finding the "wrong" bit in 10MS of 32 bit captures.
Memory efficiency is relatively unimportant, especially now memory is so cheap.
What is important is being able to ignore rubbish, so you can concentrate on what is important. That's why state-based arm/trigger/filter is so important: it saves your time. If you don't capture the crap, there's nothing to ignore.
Alternatively: good luck finding the "wrong" bit in 10MS of 32 bit captures.
Sure, for modern analysers, but I was referring to getting remaining value out of old machines like a 1630 or 16510 card. If operating in state mode you're only using one word per instruction, rather than oversampling, and per my description elsewhere you can get a lot of useful repair information out of the first few K of execution cycles (or a few K around the right trigger point). IIRC even the 1630 had a couple of levels of trigger, not just an address comparator.
Totally agree about using the trigger to reduce the amount of unwanted data though.
The low end modem LAs have very restricted functionality w.r.t. filtering and triggering. Decent modern LAs are fine, as are old LAs from that period, e.g. >HP163x.That would seem to rule out the LA features included in entry level oscilloscopes…. You’re definitely going to need a good dedicated device for this kind of analysis.
That's right. I've only ever seen timing analysers included in oscilloscopes. This is not really an LA, it's a bunch of very low resolution oscilloscope channels for use in systems where 2 or 4 analog channels aren't very useful. That's why they're called 'mixed signal oscilloscopes' rather than 'mixed domain analysers'.
The better ones offer SPI/RS232/I2C protocol analysis via oversampling which helps make sense of serial data but to usefully display an instruction stream you want clocked capture and possibly demultiplexing clocks.
When debugging/repairing equipment of that age:
- measure Vcc voltage and ripple, using voltmeter and scope
- use scope to verify signal integrity. 100MHz is sufficient, but be aware of the ringing caused by a 6" ground lead
- thereafter use a logic analyser
There are lots of options in terms of digital and analogue capture. Get the deepest memory you can afford but be aware you'll sometimes limit the capture to keep the display time down. On these parallel bus processors you'll be using it in state mode though, which is far more efficient for memory use. There is an analogue scope option. It's often pricy and is very poor compared with modern scopes, but having it in the same box with time-aligned displays and cross triggering is very powerful on a mixed-signal device like a synth.
If you have no prior experience of logic analysers I'd actually recommend doing the same thing. A 1630 (1630D for mixed signal, 1630G for software development) is very cheap and is explained in terms that makes it very comprehensible to a hardware engineer. Later models lacked that straightforward explanation and wrote the manuals in terms of usage examples. IMHO this denies you the basic understanding of what's going on that proper understanding requires. Once you start to suffer from it's limitations, replace it with a more modern one. But your synths were designed by people using that class of analyser - upgrading to a '90s machine is the lap of luxury, adding small probes, deep memories, bigger / better displays.
The Agilent 16702B is a modular LA with 5 slots and lots of parallel capacity (typically 68 channels per slot) and captures in state or timing mode. You can also get scope cards with limited points (32k) that allows correlated capture with the digital inputs which is useful for checking signal integrity.
Capture cards using the "40-pin probing system" are available with anywhere from 512k to 64M points, amd hacks have been discovered to configure a card to its maximum capabilities. TTL, CMOS, ECL, and custom -6V to +6V threshold levels are supported.
Z80 and other processor decoders are available. Support for modern serial protocols, such as SPI and I2C, is non-existent, although of course it will show you the waveform. Included in the OS is development software, so you can write your own decoders and disassemblers, if so inclined.
If you want something a little smaller, the 1670G and friends is a good compromise, but doesn't provide an accessible OS like the 16702B. It uses the same 40-pin probing system, as does many other from HP/Agilent units from this era.
The 1630 series was mentioned above. I had a 1631D for years, and the triggering was very sophisticated and easy to use. But I found its capture memory of only 1024 points to be extremely limiting.
What frequency do these vintage instruments run at? I’d guess many are Z80 or similar running around 4MHz or so.
A Tektronix TLA715 is available locally and I am considering this unit but I basically know nothing when it comes to the probes and adapters I need. It has two of the TLA7N4 (2GHz timing, 64k) modules installed and comes with several of the P6434 probes. Of course these probes are the ones with the Mictor connector and are of no use to me unless I buy or make a Mictor to 2.54mm adapter. I need help determining which probes would be most suitable for my application and I have allocated several hundred dollars for obtaining these probes. According to the pdf, "Tektronix P6400 P6800 P6900 Logic Analyzer Probes" from https://w140.com/tekwiki/wiki/P6434, it looks like most of the probes are compatible with TTL & CMOS levels. I need some sort of flying lead that can be attached to the pins of chips. I have made a little DIP-14/16 breakout PCB with 2.54mm pin headers that I can attach a probe to as well. The P6417 and P6418 appear to be something I can use but I would like to confirm.I have a TLA715 myself and so far I've been very happy with it (its my 4th logic analyser). A newer model is the TLA7000 series which can use the same modules.
Having a mictor to flying leads adapter is one way to go. I have made something like that a long time ago.
If you want to hunt for flying lead probes, make sure to get the P6417. These are the older model which has tongue shaped contacts which will grab on thin wires as well.
I see some mentioning getting USB logic analysers but I don't think these are very handy as these don't have the elaborate trigger and storage qualifiers a real logic analyser has. What the TLA715 can do is store only when a signal changes. This means A) you can use read/write strobes, chip selects, etc to get a list with addresses a microprocessor is accessing and thus trace which memory locations are accessed B) you need far less memory to store a long sequence of accesses and still you retain full samplerate time resolution. This is a very powerful feature when dealing with microprocessor circuits like the ones you are describing. Another possibility is to take a snapshot of samples around an event which can help to find what the signals look like before and after an event (for example: see what happens in surrounding logic when a setting in hardware is changed).
The TLA7N4 module can be hacked to support 8Mpts per channel. You have to send a few simple commands over the TekVISA control panel to do this. More info can be found on this forum.
They might be useful to sku_u but he's looking for solutions to microprocessor-based instruments with external ram and rom, which often fail because of address decoding or data bit errors. A wide logic analyser is kind of overkill but does actually do a really good job as long as you have a decent probing solution.
For machines with a 40-pin DIP CPU (a lot of them !) I recommend a 40 pin dip clip with the LA probes connected to address, data and control signals - enough to get an instruction trace. Maybe add a few external signals such as chip selects on rom and ram chips. Capture the first few hundred cycles out of reset. This is long enough to do plenty of instruction fetches and, critically, some stack access,
Examine the trace, verifying :
1. What happens at reset ? Typically it should fetch a reset vector, access a ROM and then start executing there. Is it sensible ?
2. Are all the data bits active ? any appear to be shorted together or stuck high / low ?
3. Watch a call occurring (the PC should get pushed onto the stack, maybe with other things)
4. Find the corresponding return. Does the same value get pulled from the stack or has it been corrupted ?
These will show up most of the common problems around a CPU/RAM/ROM core. You might be able to extend it to some I/O and a larger range of address bits but I have used this heavily when training production technicians to debug new builds that pass ATE but don't work. Both 8086 and ARM2/3 machines. These are especially hard because they often have multiple faults - they have NEVER worked. Most repairs are on bits of equipment that worked until they got a fault and then were sent for repair - so they only have one fault. Old equipment thats been rusting for years may have more but they're often in very different areas (logic, power supply, hard discs).
This procedure feeds back into the initial question slightly.
You want an LA that's wide enough for all address, data and control buses and a few extra too. This means 32 bit for 8 bit machines and more for 16 bit machines. Not many 32 bit busses in this era. but Acorn Archimedes is an exception - though the conditional instructions makes it a bugger tom determine execution path other than through the address bus.
Some machines (8086, Z80) have a multiplexed address/data bus. Thius reduces the nuber of pins you need to moinitor but requires a state clocking mechanism that can record both data and address phases. I think this needed an external hardware bus processor for the 8086.
Huge depth is not necessary (though it's nice). Even with 1k depth you'll usually see a stack call & return, and if necessary you can trigger on ram accesses over a small address range. This is the advantage of the complex state triggers these LAs have.
A disassembler (possibly including special hardware) is also very helpful to make the instruction stream more readable.
Another device that has a bit of a premium price because of rarity and the appreciation of it by, especially, arcade techs, is the Fluke Troubleshooter. This is a simplified in-circuit emulator with personality pods to suit popular processors. The processor is removed and the pod end plugged in its place (it may be possible to clip over a soldered-in device).
The troubleshooter then runs a bunch of canned tests such as ram, rom checksum, address and data bus etc. by generating bus cycles at the processor that exercise those things without requiring the real roms and rams to work. I think it has an actual processor in the pod, it's not just a digital vector generator, but that processor is using its own rom and ram and then steering the bus access internally or externally to suit. This can give very rapid detection of shorted or open data and address busses.
I'm not sure if there are enough machine of this era needing repairs to justify the development effort, but it could be reproduced using something like a Pico. Maybe worthwhile for fixing pinball machines which have large numbers of different designs having a common CPU board.
FWIW I was playing around with my DSlogic LA today and noticed that it has a full Z80 decoder available. You might have to play around with triggering options as discussed above, but you can capture and filter addresses, data R/W etc pretty easily. With the large memory ability provided by streaming capture, you could easily analyze the startup process to verify proper operation.
Just figured I’d mention that as it seems like it would be helpful for working on that type of gear. I see that the OP wants a stand-alone device, so prefers a non usb LA…. But if the tool works for the task I don’t see how that applies to the issue? A stand-alone device is basically the logic hardware with a self contained processor running the box, so what difference would it make if the logic hardware and processor were separate devices? Surely there’s no lack of laptops available to make a dedicated usb LA setup? That’s basically what I do - a cheap older tough Thinkbook makes a good addition to my bench. In addition to running my LA, it also connects to my power supplies, scope, and meters for data logging. It’s a tool like everything else.
Edit - looked up the HP 16500.. very impressive. But obviously bench space is not the limiting factor if you’re looking at gear that size lol.
Thank you everyone for replying. There is a lot of invaluable information in here and a lot of points that I would have not considered if it wasn't for your comments.
Some of the key points I've taken away
-LA should be wide enough for all of the address, data, & control lines
-Triggering options
-Capture depth
A Tektronix TLA715 is available locally and I am considering this unit but I basically know nothing when it comes to the probes and adapters I need. It has two of the TLA7N4 (2GHz timing, 64k) modules installed and comes with several of the P6434 probes. Of course these probes are the ones with the Mictor connector and are of no use to me unless I buy or make a Mictor to 2.54mm adapter. I need help determining which probes would be most suitable for my application and I have allocated several hundred dollars for obtaining these probes. According to the pdf, "Tektronix P6400 P6800 P6900 Logic Analyzer Probes" from https://w140.com/tekwiki/wiki/P6434, it looks like most of the probes are compatible with TTL & CMOS levels. I need some sort of flying lead that can be attached to the pins of chips. I have made a little DIP-14/16 breakout PCB with 2.54mm pin headers that I can attach a probe to as well. The P6417 and P6418 appear to be something I can use but I would like to confirm.I have a TLA715 myself and so far I've been very happy with it (its my 4th logic analyser). A newer model is the TLA7000 series which can use the same modules.
Having a mictor to flying leads adapter is one way to go. I have made something like that a long time ago.
If you want to hunt for flying lead probes, make sure to get the P6417. These are the older model which has tongue shaped contacts which will grab on thin wires as well.
I see some mentioning getting USB logic analysers but I don't think these are very handy as these don't have the elaborate trigger and storage qualifiers a real logic analyser has. What the TLA715 can do is store only when a signal changes. This means A) you can use read/write strobes, chip selects, etc to get a list with addresses a microprocessor is accessing and thus trace which memory locations are accessed B) you need far less memory to store a long sequence of accesses and still you retain full samplerate time resolution. This is a very powerful feature when dealing with microprocessor circuits like the ones you are describing. Another possibility is to take a snapshot of samples around an event which can help to find what the signals look like before and after an event (for example: see what happens in surrounding logic when a setting in hardware is changed).
The TLA7N4 module can be hacked to support 8Mpts per channel. You have to send a few simple commands over the TekVISA control panel to do this. More info can be found on this forum.Thank you very much for chiming in about the TLA715! There is a lot of great knowledge in this forum about this unit. I am going to check out the one local to me this week. I don't have anything with Mictor connectors that I can test the unit with. Is there any other way I can test the logic analyzing capability of the unit without buying some probes I can test with? Of course I am going to do the obvious inspecting and testing that I can do. Any cons or things you wish it did that it doesn't?
Thank you for chiming in about the Z80 decoder.... this definitely makes it an interesting option. I haven't completely written off an USB based analyzer and I do have an older Thinkpad laying around...