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

[nctnico]

Nice write-up and pictures! 

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).

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.

That was one of the big questions. I have compiled a rather long list with scopes which included the Wavepro 900 series (preferably a 960) and even the Wavepro 7000 but in the end I had to be sensible and look at what unique features an older >1GHz scope would really add to my lab and the answer was: bandwidth and a noisy dog house. So I opted for a model which was relatively small, light and cheap. Spending more would mean buying features I already have. The 54835A is not going to be my daily use scope. I will only switch it on if I need the bandwidth.

[Wuerstchenhund]

That was one of the big questions. I have compiled a rather long list with scopes which included the Wavepro 900 series (preferably a 960) and even the Wavepro 7000 but in the end I had to be sensible and look at what unique features an older >1GHz scope would really add to my lab and the answer was: bandwidth and a noisy dog house.

Oh yes, these scopes are loud, and quite large.

The small and less noisy alternative would be a WaveRunner2 LT584 (1Ghz) but they are somewhat rare (and often vastly overpriced).

So I opted for a model which was relatively small, light and cheap. Spending more would mean buying features I already have.

Makes sense. I know you already have other scopes.

The 54835A is not going to be my daily use scope. I will only switch it on if I need the bandwidth.

I use my DSO8064A as my main scope now, mostly because it's less noisy and a bit smaller than the WavePro 7k. What's annoying though is how expensive active probes are for Infiniium scopes, even 2nd hand.

[snoopy]

Does this help ?

[Jwalling]

transfer lots of data in a single pass.

writing a shitload of stuff to a usb key will often cause the interface to hang after while.
i imagine any streaming devices like tuners will cause absolute chaos.
btw, the first intel chipsets with usb 1.0 had the bug too - it was in the design spec they where supplied with!!!
oops! 

I copied the entire contents (about 105MB)of the \ossetup directory folder to a thumb drive, then did a FC/B to compare the files. No errors. I'd say it's good enough for government work, when the most likely use is saving screenshots and such.

[free_electron]

here is the clip you need to press.

[Jwalling]

here is the clip you need to press.

You can't. the CH3/4 attenuator assy. covers those.

[nctnico]

here is the clip you need to press.

You can't. the CH3/4 attenuator assy. covers those.

Indeed but it seems to vary between the models. The attenuators in my one are fully enclosed in (bulky) metal shielding so there is no way I can get to the clips.

[Jwalling]

here is the clip you need to press.

You can't. the CH3/4 attenuator assy. covers those.

Indeed but it seems to vary between the models. The attenuators in my one are fully enclosed in (bulky) metal shielding so there is no way I can get to the clips.

Exactly. The dual attenuators on the 54835A/45A cover them. On the 54825A and lower, they may be accessible since there's 4 separate ones.

[nctnico]

Time for an update. On the PC part I added another 256MB (I bought 3 memory modules so why not) and disabled swap (virtual memory).

More importantly I received the replacement ADC hybrid today. After swapping it the self tests pass and channel 1 works so now I have 4 working channels. Woohoooo! Time to put everything together!

I bought some standard HP feet with tilt stands but I quickly found out the 54835A uses different feet. I tried to find the right feet on Ebay but couldn't so time to pull out the drill press and drill some extra holes to hold the most common HP feet:








The end result (200MHz signal with FM modulation):


What is interesting is that the probe interface board shows a lot of use on channel 1, a little bit on channel 2 and none on channel 3 and 4. Also the attenuator relay count is very low. Around 4000 on channel 1 and around 2000 on the other channels.

[alm]

Thanks for the update. Great that replacing the hybrid turned out to be a complete fix (which was like 90% likely, but you never know until you try it).

[tautech]

Front panel USB connectivity ?

Could you shoehorn one of those USB drive bay panels in where the the floppy drive is ?

[nctnico]

Front panel USB connectivity ?

Could you shoehorn one of those USB drive bay panels in where the the floppy drive is ?

I thought about that. First of all I have not been able to find USB drive panels which fit into a slimeline 3.5" drive. Secondly and worse: Windows98 starts acting up if I DISconnect the drive. This may have to do with the fact that it isn't a normal floppy drive but a combination between a floppy disk and a 120MB optical drive (pretty amazing how they put all that into such a small space). I think I'll opt for a USB extension cable.

edit: Windows98 starts doing weird things when the LS120 is disconnected

[tautech]

Front panel USB connectivity ?

Could you shoehorn one of those USB drive bay panels in where the the floppy drive is ?

I thought about that. First of all I have not been able to find USB drive panels which fit into a slimeline 3.5" drive.

Yep, slimline will probably be hard to find but keep an eye out for something proprietary from HP, Dell or similar PC's.

[nctnico]

Thanks for the update. Great that replacing the hybrid turned out to be a complete fix (which was like 90% likely, but you never know until you try it).

Actually there still is a minor issue with channel 4. It doesn't pass vertical calibration. A quick check didn't reveal an obvious attenuator problems so maybe some gain control setting is at it's maximum.

[alm]

Interesting, given the lack of wear on that channel. But maybe they used a BNC cable or a probe that does not have power/ID pins. Could be that one of the resistors drifted after being overloaded.

[Tony_G]

Secondly and worse: Windows98 starts acting up if I connect the drive. This may have to do with the fact that it isn't a normal floppy drive but a combination between a floppy disk and a 120MB optical drive (pretty amazing how they put all that into such a small space).

All those drivers should be in images you got from my link. Mine doesn't have the super drive but I've been thinking of adding it.

TonyG

[nctnico]

Secondly and worse: Windows98 starts acting up if I connect the drive. This may have to do with the fact that it isn't a normal floppy drive but a combination between a floppy disk and a 120MB optical drive (pretty amazing how they put all that into such a small space).

All those drivers should be in images you got from my link. Mine doesn't have the super drive but I've been thinking of adding it.

I made a typo: Windows98 starts acting up when the drive is not connected.

[Jwalling]

Secondly and worse: Windows98 starts acting up if I connect the drive. This may have to do with the fact that it isn't a normal floppy drive but a combination between a floppy disk and a 120MB optical drive (pretty amazing how they put all that into such a small space).

All those drivers should be in images you got from my link. Mine doesn't have the super drive but I've been thinking of adding it.

I made a typo: Windows98 starts acting up when the drive is not connected.

The IDE channel on those FIC motherboards is a bit flakey. It doesn't like some PATA SSD drives I've tried either. Maybe the added loading of the LS-120 compensates the bus a bit. One or more ringing signals maybe?

[Wuerstchenhund]

The IDE channel on those FIC motherboards is a bit flakey. It doesn't like some PATA SSD drives I've tried either.

The IDE controller in the buggy VIA chipset's Southbridge only supports (some buggy) UDMA-33 (UDMA-2) while most PATA SSDs require at UDMA-100/133 (UDMA-5/6). Also, if I remember correctly (and that's been a long time), only the primary IDE channel even supports UDMA (I think the secondary channel is PIO only).

Personally, I wouldn't bother with SSDs on this scope. Considering the poor performance of the VIA Apollo chipset and the limitations of the OS (Win98) I guess the best option would be an IDE-to-CF adapter. CF cards that support IDE mode usually support PIO modes which might be safer with this chipset than UDMA. Newer cards (Rev. 3 and newer) also support UDMA-33 and UDMA-66 modes (some Rev 2 cards support UDMA-33 as well). A Rev 3 card should be fast enough for this application.

A practical option would be one of the expansion cards that have a CF slot in the slot cover or a slimline CF reader so the card is accessible from outside. It would also allow to easily change between multiple copies i.e. for experimentation, or having a card for each project which contains only stored settings/screenshots/waveforms for that project. It also makes it easy to copy data to a PC.

[nctnico]

The problem with IDE CF cards is that these are typically marked as removable media. Some biosses will not boot from these and some software won't install on a removable drive. I have used exactly the same mSata to PATA adapter in my Tektronix TLA715 because of these problems. Still I agree that the motherboard and CPU are rather poor choices. BTW UDMA is disabled in the VA-503A BIOS by default and probably for a good reason.

[stj]

http://www.ebay.co.uk/itm/351131265761
 

[Jwalling]

http://www.ebay.co.uk/itm/351131265761
 

The scope uses 2.5" drives, but may be possible to use that if you want to hack in a 4 pin disk drive power cable connector, and use the secondary port. Might be easier to find a 2.5" variant.
http://www.ebay.com/itm/2-5-IDE-2-5-PATA-to-scoket-2-M-2-NGFF-SATA-SSD-adapter-card-with-case/322162290175?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2055119.m1438.l2649

Than one does NOT work with the FIC board, though.

[nctnico]

http://www.ebay.co.uk/itm/351131265761
 

The scope uses 2.5" drives, but may be possible to use that if you want to hack in a 4 pin disk drive power cable connector, and use the secondary port. Might be easier to find a 2.5" variant.
http://www.ebay.com/itm/2-5-IDE-2-5-PATA-to-scoket-2-M-2-NGFF-SATA-SSD-adapter-card-with-case/322162290175?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2055119.m1438.l2649

Than one does NOT work with the FIC board, though.

This one does:
www.ebay.com/itm/Hot-Tested-mSATA-to-2-5-PATA-IDE-Enclosure-Adapter-Case-With-Screws/201268830337

[stj]

i posted that version because it matches the motherboard headers.

if you want 2.5" then here:
http://www.ebay.co.uk/itm/332247062499

[Wuerstchenhund]

The problem with IDE CF cards is that these are typically marked as removable media. Some biosses will not boot from these and some software won't install on a removable drive.

Only in CF mode. Better cards support True IDE mode which means they behave as a IDE drive (fixed or removable). SanDisk (i.e Extreme), Transcend and Apacer have several cards that support True IDE mode in fixed and removable configuration, but usually only for the industrial variants, not the consumer cards.

Also, many of the cheap Chinese CF-to-IDE adapters don't put the card in True IDE mode, which is if I remember right by grounding a specific pin. Also, they don't connect the UDMA-relevant DMAACK/REQ signal pins. Nothing that can't be fixed with a soldering iron and a bit of wire.

I have used exactly the same mSata to PATA adapter in my Tektronix TLA715 because of these problems.

Never had an TLA but I've replaced IDE hard drives in a lot of similar systems (486 and up), with the right cards and a good adapter no problem.

Still I agree that the motherboard and CPU are rather poor choices. BTW UDMA is disabled in the VA-503A BIOS by default and probably for a good reason.

Probably. Which means you'd be using MWDMA which limits the board to 16MB/s (I guess a lot less with that chipset), which puts it easily into territory even an older/slower CF card could handle.