Author Topic: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)  (Read 59657 times)

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Online joeqsmith

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #325 on: February 21, 2021, 05:56:44 pm »
Understanding vintage tech is always instructive.

One concrete goal might be to understand them better, so they can be kept in useful service for many years to come. There aren't many alternatives in this price range that have comparable specs, especially if you include AC in the comparison - so good examples are worth taking care of.

Another concrete goal might be finding a way to verify and perhaps even calibrate these meters (including aligning the A/D) assisted by a script running on the computer - so you could do it more often, with less calibration equipment (depending on how clever we can get), and thereby enjoy the benefits of having such a good specification meter in the first place - i.e. being able to use it for other electronics projects where measuring stuff very precisely / accurately is beneficial.

Everything depends on what we discover when we look under the hood.   If the code is a super complicated haystack, it won't be easy to do anything with it.  If there is some method to the madness in there, it may be possible to make changes - or it might be possible to leverage the fact that we know what it is doing, to "trick" it into something else.  Time will tell!  :D 

Going completely crazy, in theory, you could even make completely new modules to fit into the motherboard...    a truly crazy person could make a new controller board out of an Arduino, for example...   (I did say truly crazy!)   ;D

I was talking with a friend of mine about this old meter and I was suggesting making a new interface board for it that would act like the parallel interface but had Ethernet.   Basically just an FPGA, Phy, memory, clock and translators on the board.  Emulating the hardware would allow it to work without any firmware changes.   

There was a point when I had some sort of assembler/disassembler (for the 8080) that ran under CPM.   This was long after having to learn that part.  It may have ran on that old Televideo or the PC.   For the Televideo, I had a way to copy data to/from the old 5" floppy to DOS.  It seems like what ever I had would support the native mnemonics of the 8080 as well as the Z80.  Again,  this is going way way back.   When I had to learn the 8080, we were required to do everything by hand (paper and pencil).  You learned very quickly to sprinkle no-ops into your code.    :-DD   The programs were simple enough it wasn't too big of a deal.     

   

Offline SilverSolderTopic starter

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #326 on: February 21, 2021, 06:02:18 pm »
Understanding vintage tech is always instructive.

One concrete goal might be to understand them better, so they can be kept in useful service for many years to come. There aren't many alternatives in this price range that have comparable specs, especially if you include AC in the comparison - so good examples are worth taking care of.

Another concrete goal might be finding a way to verify and perhaps even calibrate these meters (including aligning the A/D) assisted by a script running on the computer - so you could do it more often, with less calibration equipment (depending on how clever we can get), and thereby enjoy the benefits of having such a good specification meter in the first place - i.e. being able to use it for other electronics projects where measuring stuff very precisely / accurately is beneficial.

Everything depends on what we discover when we look under the hood.   If the code is a super complicated haystack, it won't be easy to do anything with it.  If there is some method to the madness in there, it may be possible to make changes - or it might be possible to leverage the fact that we know what it is doing, to "trick" it into something else.  Time will tell!  :D 

Going completely crazy, in theory, you could even make completely new modules to fit into the motherboard...    a truly crazy person could make a new controller board out of an Arduino, for example...   (I did say truly crazy!)   ;D

I was talking with a friend of mine about this old meter and I was suggesting making a new interface board for it that would act like the parallel interface but had Ethernet.   Basically just an FPGA, Phy, memory, clock and translators on the board.  Emulating the hardware would allow it to work without any firmware changes.   

There was a point when I had some sort of assembler/disassembler (for the 8080) that ran under CPM.   This was long after having to learn that part.  It may have ran on that old Televideo or the PC.   For the Televideo, I had a way to copy data to/from the old 5" floppy to DOS.  It seems like what ever I had would support the native mnemonics of the 8080 as well as the Z80.  Again,  this is going way way back.   When I had to learn the 8080, we were required to do everything by hand (paper and pencil).  You learned very quickly to sprinkle no-ops into your code.    :-DD   The programs were simple enough it wasn't too big of a deal.     

 

LOL!   :-DD

I never learned 8080, but I did once write a network driver in 8086 assembler in order to be able to "hit the metal" under DOS!  Those were the days...  today, you would be arrested by the IT department for trying anything like that!   :D


I guess the kind of code that is in this instrument is why all the modern software development methods were invented, as the haystack eventually becomes unmanageable!  :D
 

Online joeqsmith

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #327 on: February 21, 2021, 07:26:08 pm »
I wasn't able to locate my books on the 8080.   There was also a cheat sheet that was provided that had all of the instructions that I wasn't able to find.   Just artifacts from days gone by.

If you like old stuff though, here are two of the original Intel evaluation kits for the 8080.  Note the letter talking about the supplied PIOs.   Guessing these kits would be fairly rare.

****
https://en.wikipedia.org/wiki/Intel_System_Development_Kit

https://www.intel-vintage.info/inteldevelopmenttools.htm
« Last Edit: February 21, 2021, 07:55:10 pm by joeqsmith »
 

Offline SilverSolderTopic starter

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #328 on: February 21, 2021, 10:14:20 pm »
I wasn't able to locate my books on the 8080.   There was also a cheat sheet that was provided that had all of the instructions that I wasn't able to find.   Just artifacts from days gone by.

If you like old stuff though, here are two of the original Intel evaluation kits for the 8080.  Note the letter talking about the supplied PIOs.   Guessing these kits would be fairly rare.

****
https://en.wikipedia.org/wiki/Intel_System_Development_Kit

https://www.intel-vintage.info/inteldevelopmenttools.htm

Wow, nice bit of history!  Did you buy that originally?

The 8080 is the father of a pretty big wave of descendants...   including the one being used to type this comment, LOL...  has it reached self awareness?  :D

I love old tech.   How can you not fall for something like this:

 

Offline Roman oh

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #329 on: February 21, 2021, 11:51:28 pm »


I've recently wasted time with google.
Everyting seems to be plently first and then finally just junk.
I tried to find an i8080 emulator that would suite for hardware testing but found nothing.
Memory says that Altavista was better.

Obviously I had to start doing my own emulator, it's still just a shell but I'll upload it if it becomes usefull.
For a moment I thought maybe Ghidra addon can do it but then later there will be an avoidable obstacle anyway.

I couldn't find a useful 8080 emulator, but there seems to be a lot of 8085 stuff out there (100% code compatible with 8080, and just ignore the different external interrupt structure (RST 5.5, 6.5, 7.5); the 8080 interrupts RST0 - RST7 are treated as software interrupts in the 8085, but the code works fine).
I had some fun putting this code into an 8085 emulator that I downloaded from Oshon Software (no affiliation). The evaluation version is free, but closes after a one hour session, and you get 30 of those sessions for free. But the licence is only 25 euro. It allows breakpoints, single stepping, modify rom, ram and registers (very useful for shortening the start-up delay at 02E4H). I spent (won't say wasted - as SilverSolder says, it's all instructive) a couple of days trying to get my haed into the code, but it seems to the epitome of the reason why spaghetti code is frowned on. I suspect it may actually be the output of an early C compiler, or somesuch - I used one of those on my CPM system in the early 80s. The code flow threads around like <delete rude simile!>.
It transfers code into RAM, which you might do if, say you wanted to configure the code on the fly according to different models or somesuch, but the code it transfers to RAM looks like simple arithmetic operations, and they appear to be executed during start-up even before it does anything that looks like determining a model. (The Oshon simulator manages to execute these "RAM" instructions OK, but because they are not part of the loaded program (which, incidentally, it seems to disassemble OK) you can't "see" (ie trace and breakpoint) these steps. Would be simple enough to fudge, if one wanted to.
And it does other crazy things that a "human" assembly code programmer wouldn't do - eg, bunches of subroutines, 3 bytes long, clear the same memory locations twice in two different places, etc, etc, etc.
It was doing my head in... and I was only doing it "because I can".
So while I shall keenly track this thread, I don't think I'll be doing a lot more on this in the near term. But I got my 25Euro worth!
 
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Offline SilverSolderTopic starter

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #330 on: February 22, 2021, 12:22:27 am »


I've recently wasted time with google.
Everyting seems to be plently first and then finally just junk.
I tried to find an i8080 emulator that would suite for hardware testing but found nothing.
Memory says that Altavista was better.

Obviously I had to start doing my own emulator, it's still just a shell but I'll upload it if it becomes usefull.
For a moment I thought maybe Ghidra addon can do it but then later there will be an avoidable obstacle anyway.

I couldn't find a useful 8080 emulator, but there seems to be a lot of 8085 stuff out there (100% code compatible with 8080, and just ignore the different external interrupt structure (RST 5.5, 6.5, 7.5); the 8080 interrupts RST0 - RST7 are treated as software interrupts in the 8085, but the code works fine).
I had some fun putting this code into an 8085 emulator that I downloaded from Oshon Software (no affiliation). The evaluation version is free, but closes after a one hour session, and you get 30 of those sessions for free. But the licence is only 25 euro. It allows breakpoints, single stepping, modify rom, ram and registers (very useful for shortening the start-up delay at 02E4H). I spent (won't say wasted - as SilverSolder says, it's all instructive) a couple of days trying to get my haed into the code, but it seems to the epitome of the reason why spaghetti code is frowned on. I suspect it may actually be the output of an early C compiler, or somesuch - I used one of those on my CPM system in the early 80s. The code flow threads around like <delete rude simile!>.
It transfers code into RAM, which you might do if, say you wanted to configure the code on the fly according to different models or somesuch, but the code it transfers to RAM looks like simple arithmetic operations, and they appear to be executed during start-up even before it does anything that looks like determining a model. (The Oshon simulator manages to execute these "RAM" instructions OK, but because they are not part of the loaded program (which, incidentally, it seems to disassemble OK) you can't "see" (ie trace and breakpoint) these steps. Would be simple enough to fudge, if one wanted to.
And it does other crazy things that a "human" assembly code programmer wouldn't do - eg, bunches of subroutines, 3 bytes long, clear the same memory locations twice in two different places, etc, etc, etc.
It was doing my head in... and I was only doing it "because I can".
So while I shall keenly track this thread, I don't think I'll be doing a lot more on this in the near term. But I got my 25Euro worth!

I looked at it long enough to realize the same thing - i.e. this code makes spaghetti look well organized...  they were severely space constrained and this was probably a pretty big software project in its day - they did what they could with the tools they had, I'm sure, so I'm not casting aspersions on the people that wrote it.

Do you know if there is a way to temporarily halt or suspend an 8080 in circuit?  - it might be possible to glean something by halting the processor at certain points during execution, and looking at the bus to figure out where it is...  letting it be its own emulator, if you see what I mean?

 

Online joeqsmith

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #331 on: February 22, 2021, 04:37:02 am »
The only thing I thought about doing with the firmware was to try and adjust the timing for the serial port.   I thought I would setup the LA to trigger on the UART while monitoring the data and address buss.   Once I have the address, I would disassemble these sections.   Guessing its an interrupt routine running off some timer.   I was then going to use a ROM emulator to hack the meter. 

The low cost programmer made it in today along with the replacement printer ports.   Working on getting their software setup now.   

Odd, Motorola, Xilinx, Altera are not even listed.  No support for the small Atmel serial parts.  It does support some of the more common parts like the small Xicor ones.  Wafer Scale supported.  Too funny.    I'm impressed with the features.  It's pretty much loaded like my old one.  There is a short test for VCC and VPP.   I ran a few 4000/7400 series part tests.   Then tried some GALs.  Not sure but it looks like there may be a problem with them.   Virgin parts check out. However, after programming, the unit will come up with pin faults.   Replicated with same results.   I'll just need to spend some time with it. 




Offline SilverSolderTopic starter

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #332 on: February 22, 2021, 06:55:04 am »
Sounds fun!  It would definitely be elite to release a new version of the software after 30 years!  :D


Meanwhile, I got my GPIB bus back in business.

I attached an interesting set of graphs:  comparing the frequency responses of two 8506A on all their different ranges, using a 3325A as the signal source.

The test setup is not "serious" because I didn't have a terminator capable of 4 Watt so had to run with "free exhausts", but the trends are nevertheless interesting.

Note that both units are to spec, as far as I could tell in a few minutes of looking, but they are definitely different!  The thermal AC modules have variable capacitors for tuning these curves, which is something I'll take a look at the next time I attempt to calibrate them - now that it's easy to perform a canned test!


« Last Edit: February 22, 2021, 06:58:09 am by SilverSolder »
 

Online joeqsmith

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #333 on: February 22, 2021, 03:13:01 pm »
Interesting data.   I don't have any way to create a stable enough waveform or to measure it to know how good the Fluke is.  I had compared it with the old HP meter and the two basically agree in all the Fluke's ranges.   Things diverge once I start getting outside the range the HP is spec'ed for.   Even at the low frequencies the HP would not tell me how good the Fluke is.   The errors from all of my sources far exceed the Fluke's specs.   This is why I decided to leave that section alone as I'm sure I would do more harm than good. 

Offline SilverSolderTopic starter

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #334 on: February 22, 2021, 03:40:29 pm »
My AC source is not stable enough to calibrate with either.   But any source is good enough to somewhat decently compare two meters triggered to sample at exactly the same time.

The AC spec gets much looser above 50KHz, so the meters being different isn't really a sign of a problem, it is just a sign of it being difficult to maintain tight production specs for the higher range attenuators, it seems?

 

Offline SilverSolderTopic starter

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #335 on: February 22, 2021, 03:46:00 pm »

Also worth keeping in mind that the AC accuracy depends on the DC section being in a good state of tune...

 

Online joeqsmith

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #336 on: February 22, 2021, 06:07:20 pm »

Also worth keeping in mind that the AC accuracy depends on the DC section being in a good state of tune...

Yeah, the manual is pretty clear on the order that things are to be done. 

Fully agree with your comment on relative measurements between meters.   I would like to have an idea of the absolute accuracy but outside of renting a calibrator or shipping it off I don't have any options.  Even if it were not aligned and just calibrated with a report, we could have some idea how it behaves.    Good topic for the met group.

Online joeqsmith

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #337 on: February 23, 2021, 03:01:16 pm »
Just a link to the last time I attempted to get DOS and a PCIe printer port working together.  This hack worked fine up until the lightning storm damaged the programmer and port.    With the low cost programmer missing so many of the parts I use, I plan to add another DOS based vintage programmer to the mix.

https://www.eevblog.com/forum/chat/printer-ports-for-the-modern-pc/msg1017048/#msg1017048

I did try the low cost programmer with some C256s and it seems to work fine with those. 

Offline SilverSolderTopic starter

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #338 on: February 23, 2021, 04:06:47 pm »

I can see it being a bit of a challenge to get parallel ports to work on modern motherboards.   Maybe set up a period PC just to run this stuff?  (With a CRT of course!) :D
 

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #339 on: February 23, 2021, 05:16:31 pm »
I was able to locate that same PCIe card.   As before, it passes that self test w/ the loop back connector and I was able to control the port with debug under DOS.   So pretty much back to where I started in the other thread except using the next generation programmer.   Sadly, the software is no longer offered for it but on the plus side, there is the internet.  And with the power of Google,

http://www.bitsavers.org/test_equipment/modularCircuitTechnology/jdr/

Time to hack some DOS code. 

This programmer supports U18 (74S287) which is not supported by the TL866.  No real surprise as that programmer is very limited.   On my board, the part is soldered to PCB.  Dive in and hack the Fluke or leave it.....

Offline SilverSolderTopic starter

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #340 on: February 23, 2021, 05:35:25 pm »
I was able to locate that same PCIe card.   As before, it passes that self test w/ the loop back connector and I was able to control the port with debug under DOS.   So pretty much back to where I started in the other thread except using the next generation programmer.   Sadly, the software is no longer offered for it but on the plus side, there is the internet.  And with the power of Google,

http://www.bitsavers.org/test_equipment/modularCircuitTechnology/jdr/

Time to hack some DOS code. 

This programmer supports U18 (74S287) which is not supported by the TL866.  No real surprise as that programmer is very limited.   On my board, the part is soldered to PCB.  Dive in and hack the Fluke or leave it.....

Don't turn it on, take it apart!  :D

Is U18 just programmed to work as a chip select?

 

Online joeqsmith

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #341 on: February 23, 2021, 06:01:23 pm »
That's what it looks like to me.  A PROM in place of a PAL for that era.   

I read through the thread you started about disassembling the proms but right from the start I was lost.  The first thing I would want to do is map out the entire hardware and that starts with this decoder.   Or I really missed something.

Offline SilverSolderTopic starter

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #342 on: February 23, 2021, 06:58:59 pm »
That's what it looks like to me.  A PROM in place of a PAL for that era.   

I read through the thread you started about disassembling the proms but right from the start I was lost.  The first thing I would want to do is map out the entire hardware and that starts with this decoder.   Or I really missed something.

You are right, that would be a good approach.  If that PROM is desoldered, can the contents be read by your period-accurate programmer?

It would be good to get to a programming model of this thing.  We are pretty close already, just by deducing from the code...
« Last Edit: February 23, 2021, 07:01:32 pm by SilverSolder »
 

Online joeqsmith

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #343 on: February 23, 2021, 07:24:26 pm »
I hacked the code and tried it out.  Back in business.  I don't think the 8080 will be this simple due to the lack of good tools.  First thing I want to know is if the GALs I tested in the cheap programmer were damaged.   

Yes, the old programmer supports this part.   I just need to remove it.  You can see why I am starting to think about a junk meter just for hacking.   

I will upload the image once I have it.    My guess is that thing is loaded with a lot of 1's and a few 0's sprinkled in the mix. 

Offline SilverSolderTopic starter

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #344 on: February 23, 2021, 07:31:08 pm »

Yeah, I've also got a "mule" meter for hacking/testing/repairing modules.  I like having at least two of each boat anchor because they can be hard to troubleshoot if you don't have a working one to compare with!

>My guess is that thing is loaded with a lot of 1's and a few 0's sprinkled in the mix.

A remarkably astute guess, you might just be right!  :D
 

Offline m k

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #345 on: February 23, 2021, 07:41:15 pm »
And with the power of Google,

Like when I couldn't remember witch one the LPT1 address is and tried google.
It wasn't there, I had to change to I/O map and first one didn't even have LPT2.

Maybe Altavista had better SNR.
Advance-Aneng-Appa-AVO-Beckman-Danbridge-Data Tech-Fluke-General Radio-H. W. Sullivan-Heathkit-HP-Kaise-Kyoritsu-Leeds & Northrup-Mastech-OR-X-REO-Simpson-Sinclair-Tektronix-Tokyo Rikosha-Topward-Triplett-Tritron-YFE
(plus lesser brands from the work shop of the world)
 

Offline SilverSolderTopic starter

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #346 on: February 23, 2021, 07:48:19 pm »
And with the power of Google,

Like when I couldn't remember witch one the LPT1 address is and tried google.
It wasn't there, I had to change to I/O map and first one didn't even have LPT2.

Maybe Altavista had better SNR.

If you put Google in "Verbatim" mode, it becomes almost usable.
 

Online joeqsmith

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #347 on: February 23, 2021, 08:52:34 pm »
Google  "ISA" "printer port" "address"

Second hit was
https://en.wikipedia.org/wiki/Parallel_port

Which states:
Most PC-compatible systems in the 1980s and 1990s had one to three ports, with communication interfaces defined like this:

    Logical parallel port 1: I/O port 0x3BC, IRQ 7 (usually in monochrome graphics adapters)
    Logical parallel port 2: I/O port 0x378, IRQ 7 (dedicated IO cards or using a controller built into the mainboard)
    Logical parallel port 3: I/O port 0x278, IRQ 5 (dedicated IO cards or using a controller built into the mainboard)

If no printer port is present at 0x3BC, the second port in the row (0x378) becomes logical parallel port 1 and 0x278 becomes logical parallel port 2 for the BIOS.


Of course, having used the PC since the start,
debug   - start the debugger
d 40:0  - display the addresses of the printer ports in order

That stuff seems embedded in the memory banks.   :-DD

Online joeqsmith

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #348 on: February 24, 2021, 03:12:33 am »

Yeah, I've also got a "mule" meter for hacking/testing/repairing modules.  I like having at least two of each boat anchor because they can be hard to troubleshoot if you don't have a working one to compare with!

>My guess is that thing is loaded with a lot of 1's and a few 0's sprinkled in the mix.

A remarkably astute guess, you might just be right!  :D

Well, I'm at a total loss about U18.  I removed the device without damaging the PCB and installed the same type socket so it looks somewhat the part.   My board uses a DM74S287N.  The programmer supports it no problem but when I read it, the results are very unexpected.  I did reinstall the part and powered up the meter.  No problems at all.   I wonder if this is a problem with my programmer or if this is really the contents as it appears all the bits were set (this part is cleared to all zeros).  If anyone has a programmer that supports it, I would be very interested in knowing if you have the same results. 

When is the last time you heard of Titanium Tungsten Fuses? 

Also, I had mentioned that the cheapo programmer was having a problem with some Lattice GAL22V10Bs.   I tested the parts I thought I may have damaged in the real programmer and no problems.  They erase and program just fine.   So I put them back into the TL866II plus and the problem again repeats, bad pins.  But I noticed that it works correctly the first time every time.  Then I noticed that if I repeat the same process, Read for example, too fast, the pin error happens.  Almost like I am dragging down a supply and it takes time to recharge.   :-DD


Offline SilverSolderTopic starter

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #349 on: February 24, 2021, 06:05:37 am »
The file you attached isn't cleared to all zeroes?  Here's what I see in the file, it looks interesting - note the '07' snuck in line 1 and line 9.

« Last Edit: February 24, 2021, 06:11:25 am by SilverSolder »
 


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