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rob.manderson:
My latest aquisition is an HP59401A GPIB Bus Analyser. Got it for US$15.35 - the shipping was $29.99 :) (I await Bitseeker's comment of 'Ah, so that's who got it'! :-DD)
Out of Seattle so my guess was it was from Boeing - and sure enough there's the Boeing sticker on the top. The seller claimed it was taken from a working system. Uh huh - I can't think of a single reason, in 2018, for a GPIB bus analyser being in a production line system (which is the implication I read into 'taken from a working system').
Anyway it doesn't work. Front panel character display shows nothing (though the control line leds seem to be showing valid states). I'm about to dive in and find out what's wrong. I'm guessing power supply (fingers crossed).
I searched and searched but could find no online schematics. Yep, there's an operators manual but no schematics. Fortunately Artek have it so there's another 15 bucks. I'm almost starting to think it might have been cheaper to buy the HP/Agilent usb adapter and have done with it. But I'm into the money pit now.
So why, in 2018, would anyone actually buy this dinosaur (1975ish design)? I'm trying to get Emanuele Girlando's arduino code working! It works fine against my HP5335, HP3325 and HP3456 instruments, but my HP8568 doesn't want to play nice. I'm convinced there's something in the arduino code that's not quite right.
The problem is that the HP8568 locks up after I send it a command with the REN line asserted. By locks up I mean that the display freezes. Switch back to local and it executes the command and the display becomes active again. If I leave REN unasserted the HP8568 behaves properly except that it doesn't light up the REM indicator. And leaving REN unasserted for the other instruments means they never go into Remote mode (but still respond to commands and return data).
Yes, I've considered the possibility that there might be something wrong with the HP8568 but it seems unlikely. My reading of the HP8568 service manual doesn't show anything like a Listen or Talk only mode.
bitseeker:
Ah, so that's who got it! :-DD
Sorry to hear it's not a happy camper, Rob. Yeah, hopefully, it's just the power supply. If it becomes too much to fix, it's sure to have lots of nice GPIB parts and these old HP enclosures are great for repurposing. It'd be great to see it working again, especially for the Girlando interface debugging.
I look forward to hearing more about your findings on both fronts.
rob.manderson:
lol - glad you took that comment the way I meant it :-DD
Nope - it's not the power supply. Seems to be somewhere in the clocking. I'm seeing no activity on any of the display multiplexer lines. They don't seem to have used a crystal to generate the internal clock - it looks like a multivibrator fashioned out of a 7438 and a 7414 schmitt trigger. However, it doesn't want to work on an external clock either so I'm digging around at the logic in that area. It doesn't help that I'm dredging up 35 year old memories of working on TTL :-)
This beast is so old it's all TTL with a couple of MOS memory chips - it has a whopping 32 character memory! There are a couple of PROMs, one for the character generator and I'm assuming the other forms part of a state machine. The manual is somewhat light on details like that. Surprisingly, the manual *does* list the contents, in octal, of the proms! Also, quite surprisingly, most of the chips are marked with both the HP part number and the corresponding known to the rest of the world as... part number. Even the transistors in the power on reset circuitry are marked as 2N3904's.
Ah, but it's all fun and a challenge. I really enjoy repairing stuff of this vintage.
bitseeker:
--- Quote from: rob.manderson on August 04, 2018, 06:27:15 pm ---lol - glad you took that comment the way I meant it :-DD
--- End quote ---
No worries. I actually lol'd when I saw it as I didn't think I had posted it so much that it had become a meme. Too funny.
--- Quote ---...snip...
Ah, but it's all fun and a challenge. I really enjoy repairing stuff of this vintage.
--- End quote ---
There doesn't appear to have been a teardown or repair thread for one of these. If you're so inclined, it'd be cool to start one to document the old beast, share your findings, and see who else might have one or be familiar with it.
precaud:
I've had one for over 20 years, but never found it to be useful when troubleshooting a GPIB setup... :-//
The problem was almost always my code :)
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