Products > Test Equipment
Agilent 54835A scope (4 channel 1GHz / 4Gs/s) repair & uphack
<< < (46/80) > >>
Jwalling:

--- Quote from: Gandalf_Sr on February 24, 2018, 04:21:52 pm ---Thanks, I've been looking at this one on eBay but when I zoom in on (open in a new tab) the picture, I can see a 'rejected' sticker at the top and a red 'X' alongside input number 2 - I assume a bad input channel is something that's hard to fix?

--- End quote ---

Probably a bad attenuator or A/D converter. Easy to fix if you have the part(s) as they are easily removed. A/D converter is socketed, and the attenuator is held in by a screw or two. It says "see attached tag" Ask the seller if the tag is still on it, and what it says if it is.

EDIT: The attenuators were VERY problematic on those... Suitable donors can also be found in the 54540A 54542A and the 2CH variants.
The bid on that unit is from Watronics https://www.ebay.com/usr/watronics  He used to work for HP. I had an email conversation with awhile back about why they had so many problems. Apparently HP/Agilent knew about it, but were never able to figure what the exact problem/cure was. I think that the problem was the leaf contacts on the shuttle relays were making poor contact with the gold plated posts.

Gandalf_Sr:
Thanks, it went for $212 plus shipping but I missed it, a reasonable price I think.  I'll keep looking.
analogRF:
I've got an older HP branded 54845A which was failing several tests and all calibrations. I have fixed everything up. Replaced the hard drive with a compact flash, fresh install of win98 and the software with all the upgrades up to V4.5 and added memory (64MB now from 16MB before). Cleaned up the ADC ASICs etc... and now the scope passes all self tests (multiple times), passed all calibrations and everything is honky dory except a peculiar issue that was also there in the beginning when I got the scope (it used to be win95 and SW V3.72)
As you can see in the pictures, when the graphic display is enabled, all is fine and the scope works perfectly. As soon as I disable the graphic display (top right corner) the waveform is segmented as you can see. The issue is very visible on fast time bases but it also exists on slow time bases specially with low frequency square wave it is very visible and distorted
For the life of me I cannot figure out what can be wrong with it. I don't think it is the acquisition board. When I got the scope I thought it was a software/driver issue so I replaced the clunky noisy hard drive and upgraded the software but the problem persists. The only hardware issue I can think of is the display board on the PCI slot but what is in there to test?
Tony_G:
Does it happen if you remove the additional memory? The only thing I can think of is that something is going wrong on writing the bits out to the video card memory - Maybe a DMA conflict or something like that.

TonyG
analogRF:
yes it does. I have played with memory chips. As i explained, this also happened in the beginning before any upgrades with 16MB original RAM and win95 and V3.72.
I have no idea where to go from here...actually I just noticed if you look at the photo that I posted, when the graphic display is disabled it seems the graticule lines are not even anymore! two of them are spaced further than the others it seems...i have to check this when I get home...
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod