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Agilent 54835A scope (4 channel 1GHz / 4Gs/s) repair & uphack

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stj:
there are 3 in the family,
the 503, the 503A and the 503+
i cant remember the differences,
but one has both AT & ATX power connectors and sockets for both 66MHz 72pin sims, and 100MHz sdr-dims.
(i have that model)

nctnico:

--- Quote from: free_electron on July 09, 2017, 07:17:48 pm ---no need to peel the front label off to remove that probe interface board.  from inside the scope : between bnc of channel2 and channel3 you will see 2 metal clips. simply press those and the netire pcb including the metal stiffner pops off. you don't need to muck with the screw nor destroy the front panel....

--- End quote ---
I looked again but with the attenuators fitted it is impossible to get to those clips. There is a square hole as well. Maybe that is to be used to push the probe connector panel out. BTW someone before me already peeled the sticker off in the places where it is mostly damaged. Maybe I can get things to improve by melting the glue a little bit.

Jwalling:

--- Quote from: nctnico on July 09, 2017, 09:32:11 pm ---
--- Quote from: free_electron on July 09, 2017, 07:17:48 pm ---no need to peel the front label off to remove that probe interface board.  from inside the scope : between bnc of channel2 and channel3 you will see 2 metal clips. simply press those and the netire pcb including the metal stiffner pops off. you don't need to muck with the screw nor destroy the front panel....

--- End quote ---
I looked again but with the attenuators fitted it is impossible to get to those clips. There is a square hole as well. Maybe that is to be used to push the probe connector panel out. BTW someone before me already peeled the sticker off in the places where it is mostly damaged. Maybe I can get things to improve by melting the glue a little bit.

--- End quote ---

There is a little metal "nub" that you can push out from the inside with a small flat-blade screwdriver. I'd be surprised if there's no info about it in the service guide...
I'll take a picture tomorrow and post it.

Done. The metal nub is highlighted. It's right below the CH3 BNC.
Edit: Crap - that was the 54831B. I'll try again in a bit...

Here it is.

karkoon:
Nice write up. Thank you.


Typed with thumbs.

Wuerstchenhund:
Nice write-up and pictures!  :-+


--- Quote from: nctnico on July 08, 2017, 12:45:09 pm ---I have been hunting for a 1GHz+ scope for over half a year. I prefered one which has a high enough samplerate to do this in a single shot. Ofcourse it is 'easy' to spend several $k on a Lecroy Wavepro 7000 series or something similar but I didn't want to spend that much and avoid too much overlap with the oscilloscopes I already have. The older Lecroy LC584 is also interesting and I nearly got one but the Ebay seller bailed out on me (I did got a refund though).
--- End quote ---

Well that's bad. But there should be plenty of similar scopes on the market.

There recently was a WavePro 950 (1Ghz 16GSa/s) for less than £1k on ebay UK (maybe it still is) but I guess it depends on what you wanted to spend.


--- Quote ---I also looked at the Tektronix TDS694C and TDS784 but the problem with these scopes is that they are older than the Agilent 54835A, have an obsolete NVRAM (SRAM + battery) inside and need special calibration software. The 54835A OTOH can calibrate itself using the auxilary output so it doesn't depend on calibrations values or options stored in a NVRAM. Big plus!
--- End quote ---

It's a nice feature, although most newer DSOs shouldn't show a noticeable parameter shift even more than a decade, unless something is broken.


--- Quote ---My main application for the 54835A is looking at high frequency signals (digital and analog). The 54835A has a maximum depth of 65kpts on 2 channels and 32kpts on 4 channels and no peak-detect. I guess that if you don't want to spend much then deep memory and peak-detect are out of the window. OTOH the 54835A has a lot of tools for signal analysis like FFT, color grading and stacked/chained math functions.
--- End quote ---

Don't expect too much, especially on a Windows 98 unit. You get a bit more than with an older InfiniiVision scope, but it shows that these Infiniiums were HP's first attempts at doing a Windows scope. The 54835A was designed as a general purpose bench scope, not as an analysis scope, where its capabilities are more limited. The architecture is really super-slow, but the old Win9x models with Socket7 mobo even managed to strangulate this slow architecture through its even slower PC part (slow and buggy VIA chipset). Also, not all Win9x variants can be upgraded to XP, which is recommended so you can use the later software which contains more functions and lots of bug fixes.

Also, reliability wasn't exactly great on these Infiniiums. We had lots of them and lots of problems with dead ADC hybrids, acquisition board issues, trigger issues, issues with the interface card and dying PSUs. Agilent only really got a handle of that with the successor Infiniium DSO8000/DSO80000.

As other said upgrading isn't easy because of the different interface cards but frankly going beyond the K6-3 450MHz won't offer you much performance improvement as when you go to a P2 or faster the architecture becomes the limiting factor (and the Windows part is only used as display on these scopes). I'd still consider getting a P2 board with ISA slot to get rid of the buggy VIA chipset, though.

Depending on what you want to do, a DSO8104A (which with some patience can be found <$1500) might have been a better option (although even my DSO8064A's BW exceeds 1GHz), as it has a faster architecture without the antique C&T65500 secondary graphics adapter and hardware mixing, runs XP on a late P4 mainboard with PCIe, SATA and fast onboard gfx, is much more reliable, offers up to 128Mpts memory (unlockable via hack) and 32Mpts FFT, and even has Peak Detect which seems to be important for you. Also the XGA touch screen is a notable improvement over the VGA display of the 54800 Series, as traces look cleaner and you can get more information on the screen (although you probably still want to use a mouse).

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