HP54855A repair and bring up - Page 1
Forum section: electronics / repair

author: sj_phz
author_rank: Newbie
timestamp: July 09, 2025, 07:29:34 pm
content: Hi lads,I'm starting this thread as a bit of a "Someone please help me" and a bit of a "hey someone might want to see what I've done on this end, maybe I can help some souls out." situation. I'll do my best for the latter first and then start begging for free engineering consultation.Soooo, first things first: I bought an Agilent HP54855A about a week ago on Ebay because I'm an impulsive twit who blew up his other oscilloscope while trying to confirm his antenna beam pattern in his garage. The older scope was from like 1990, and I didn't honestly want to go through the effort to fix it just yet. The Agilent HP54855A is capable of 6GHz signal capture, and it cost me about $2500 to buy from a vendor that was a 30 minutes drive away from me. The vendor hadn't tested it, and he didn't seem to know how it worked either. After locking in the sale, I picked up the scope and began diagnosing.Look at this beaut.Before I get into this, let me post some important links.This is the archive of the keysight data on their ftp server. I emailed keysight to get any help directly from them and they told me to buy a newer scope lol.https://ia800404.us.archive.org/view_archive.php?archive=/4/items/ftp.keysight.com/2015.03.ftp.keysight.com.tarThis is the personal archive of a guy who got a copy of the isos and upgrades for himself.https://1drv.ms/f/s!Amqar8_XQ9Uzj6YhN1xHdM8tQdKMOADrivers however are a mystery. One person uploaded them on his google share drive, but this has been lost to timeIf anyone can summon him, his user name is Converterhttps://www.eevblog.com/forum/profile/?u=121859If we can get these W98 drivers, I'll link them onto the top of this thread.Someone also uploaded the schematic for the power supply to the product line. This is extremely useful because scalpers are currently charging $500 for these PSUs on ebay.https://www.eevblog.com/forum/repair/hpagilent-infinium-548xx-scope-power-supply-schematic-!/Other discussion threads:https://www.eevblog.com/forum/repair/agilenthp-54845a/https://www.eevblog.com/forum/testgear/agilent-54835a-scope-(4-channel-1ghz-4gss)-repair-uphack/http://www.dasarodesigns.com/projects/fixing-an-hp-agilent-54845a-infinium-oscilloscope/I'll periodically update this as time goes on.Soo for my scope in particular.Problem 1: Mobo CMOS battery dead, easy fix and replace.Problem 2: Hard drive was yoinked out. Found this huge second hand warehouse in Berkeley CA that had a PATA hard drive hiding in the corner. And some floppies.....Problem 3: BIOS is from the mid 90s, before anyone considered USB flash boot. So I can't install a boot loader that way. Also it doesn't recognize external CD readers.I solved this by digging up an old PC from the early 2000s that still had a CDR writer. I had some extra CDs which made life easier. So the first thing I did was install a boot loader that will let me boot from USB flash. This is called plophttps://www.plop.at/en/bootmanagers.html. Since the CD drive on the scope was clearly dying, my first thing was to have it boot into free dos on a USB flash, while including plop img on the USB so that I could boot from one of the floppies I purchased. Unfortunately Karen's 1997 tax return, still left on the floppy, was lost in the collateral damage.With plop installed on the floppy, I can now boot into freedos whenever I'd like and we can start loading up those recovery images onto the HDD.Problem 4: Oops plop mounts the flash as your main HDD and doesn't mount any other HDD sorry.Problem 5: Oops ghost crashes on freedosProblem 6: Oops freedos doesn't have rawrite--gotta download rawrite.Problem 7: Oops the backpack image doesn't work for whatever reason, keeps arguing with me about fonts and not detecting the recovery CD even if its in the drive. I blame this on the older CD drive.I fixed this with a one two punch by flashing MS DOS 7.0 onto two floppies. Then installing MS DOS onto the hard drive, then booting to the hard drive. After this, I ran ghost without issue from a floppy and installed the HPSCOPE4x.iso recovery image.Well shoot. I'm stuck in the same boat as other users where the drivers are not properly loading and windows is trying to force its incorrect drivers on the hardware. If hit cancel on the driver installs, windows just crashes eventually. If I install 3_5_rec.iso file, which I think is the original recovery CD, it crashes before displaying anything on the screen. Both of the versions will boot into safe mode (You do this by editing msdos.sys and changing safeboot to 1), but I'm unable to install anything properly in safe mode.I tried installing windows XP via M815G-T3A-Disk1.iso (Disks 1-4) and to its credit, all devices properly enumerate and there's no driver issues. However I cannot find the software that actually opens up the scope, and the software provided by this .iso seems to be unable to open my hardware.I also tried the "Pholyrecovery.iso" file linked here:And while it makes it to the actual desktop, there's still no evidence of the devices properly connecting.I'm kind of at my wits end with this, because I have no idea where to start on my drivers and I have no idea if someone harvested this device and mixed/matched hardware or something along this line of thinking. I would have imagined that this device is plug and play after the ghost install.This is the hardware installed on my system. So you'll have to tell me if this is incorrect:Motherboard: VP22 REV A4 (AG-0960-2481)GPIB Bridge board: HP 54855-26515Video display module: HP 54810-66529 Rev 003PCI Video Module: HP 54810-66525Acquisition assembly: HP 54855-69513Acquisition power board: HP 54855-66514 REV AAttached is a photo of my upper assembly as well:Honestly the only thing that sticks out to me is the fact that the PATA/IDE connectors are going to the mother board and not to HP 54810-66529. However, I don't know if my version of the device requires that.Does anyone have any advice for how to proceed? Has anyone found themselves in a pickle like this before? I summon the electronic wizards and offer my eye to see better.Notes:*I did check the power rails on the PSU, and calibrated them to be as close to their range as possible. One of the 3.3V rails is 3.5V unfortunately, but I figure that's probably not going to cause a huge issue. In addition, there is some odd behavior on the Acquisition power board. The -12V DC rail has a 1V AC swing on it, and so does the -5V rail. There's also a capacitor that's adding noise onto a single circuit, but that circuits output (-5V for an isolated rail) appears to be unaffected.*Nothing seems to be any obvious reason for why the system isn't properly enumerating on win98.*I've ran memtest86, everything passes.

author: sj_phz
author_rank: Newbie
timestamp: July 09, 2025, 11:31:17 pm
content: WELL! It is always darkest before the dawn. And lets be clear I still have no idea how to get this thing working in win98. But the scope works now in windows XP. What did I do? Well I spent the past two days scratching my head looking for the fabeled "Agscope.exe" and yet was none the wiser to simply look at the official keysight website. It's like when an abusive parent surprises you with the new copy of call of duty and you think they love you again--except its with keysight.Here's the link to the scope softwarehttps://www.keysight.com/us/en/lib/software-detail/instrument-firmware-software/infiniium-8000-series-80000-series-5485x-series-and-5483x-series-oscilloscope-software-566904.html. All I had to do was install the windows XP partitions, then the scope software. Drivers be damned. All tests passed. 8k gain in value by installing a hard drive onto a "dead" scope.Again, if anyone could please summon whoever has the win98 drivers. Not because I'd use them but because I'm sure someone has a scope that isn't compatible with win xp and we should spread the love.

author: KE5FX
author_rank: Super Contributor
timestamp: July 10, 2025, 12:18:00 am
content: Great work. I, too, have been tempted to upgrade my TDS 694C to one of these 6 GHz+ Infiniium models, but I always talk myself out of pulling the trigger for fear of getting myself into the same kind of trouble you did. I spentmore than enoughtime screwing around with DOS and Windows 9x back in the DOS and Windows 9x days.

author: sj_phz
author_rank: Newbie
timestamp: July 10, 2025, 04:10:53 pm
content: QuoteHa! I sure got a taste of that!Now after starting my qualification of the scope, I noticed that inputs 2-4 are not working. I traced it down to the attenuation circuit, 1NB7-8518. The chip itself is a bit of a mystery, as there's no datasheet for it

author: GGMM
author_rank: Frequent Contributor
timestamp: July 11, 2025, 07:24:55 am
content: Sj_phz,There are at least 2 of us struggling with these old oscilloscopes.I managed to put an SSD drive and replace the Atlas 757 card with a trend 7110M. begin to work but...By I am at this question, because the tests of the video card are good, but everything that is acquired is in error.see here:"I retrieved a card 66525 and a card 66529.Physically they are the same the original cards, but have a Rom1.1 versionSimple question, can we pair a 66525 with a 66502, or is it absolutely necessary to have a 66525 and a 66529?"see post:https://www.eevblog.com/forum/repair/the-early-repair-of-agilent-54810a/25/cdt

author: sj_phz
author_rank: Newbie
timestamp: July 11, 2025, 02:06:17 pm
content: Quote from: GGMM on July 11, 2025, 07:24:55 amI gave a reply in your thread.Back on topic,OOOF, these attenuator units hurt. After a quote for 1NB7-8518 from omo-ic, they want $280 per on these units. There's a guy on ebay who has a dead scrap board for this scope, also local, that I'm trying to haggle down to $300. However from what I see, these attenuators are nicely soldered onto the PCB and I'll need equipment not available in my house for it. I'm kind of caught in a position where I don't want my ego to win, EG: have me buy one of these scrap boards, then try to replace a delicate component on a pcb where I have only one of each. In an ideal world I'll probably provide the parts and pay a repair tech to do it for me, with insurance of course hahaha.The other problem however is likely what broke these ICs. There's a 500mV ripple on nearly all DC rails on this device, and the -5V and -12V rails have a 1V ripple. Unacceptable. Completely unacceptable. One specifically problem IC is PT4582A, where it is letting out a high pitched whine. Originally I thought this whine is from the filtering capacitor adjacent to it, but unfortunately this is not the case. Depending on how the system uses the +12V and -12V signal, this component could be adding the ripple on everything else.(IC on the left is the +12, -12V to +5, -5V converter).You can see from my thermal image that the switching fet and the inductor are getting quite hot. Hotter than anything else on the power board.No thermalThermalUsually my rule of thumb is that if anything breaks 60-70C then its usually not working correctly. Obviously this is false at times, but it's a good rule of thumb.These converters are about $50, which isn't too bad until you realize that Rochester won't sell you anything unless you order 6 ea or $250 worth of stuff. So I'm back to the drawing board. The mosftet on there is likely Si7898DP,https://www.mouser.com/ProductDetail/Vishay-Semiconductors/SI7898DP-T1-E3?qs=jcx%252B0HVgj2Y5nFUXmPvM0w%3D%3Dbut I might want to get some calipers to confirm the dimensions. Also, a completely off topic note, but chatgpt o3 is actually getting strikingly good at helping me recognize SMD components with confusing labels printed on them. Bravo to them. It still doesn't understand circuits for the life of it, but maybe that's a good thingAnyways, until I get some quotes back I likely won't be working on this. I also am not comfortable touching this RF assembly without proper equipment (such as ESD mats, board heaters, ovens maybe, heat guns with directed heat, copper tape etc.) so I might want to sent this off to someone who solders all day and I could get insurance on. If you see right here, an amateur got to soldering a replacement already onto this board and either gave up or did it improperly. Flux is everywhere and honestly its quite possible that they never tinned those pads and there's an improper electrical connection. Without the install notes on that smd Idk. I'd at least do something like tin those pin to pad connections with a 30AWG solder but I wouldn't touch it without a microscope and esd protection at a minimum, which are things I don't have rn.

author: sj_phz
author_rank: Newbie
timestamp: July 11, 2025, 07:49:25 pm
content: Update, I ended up buying an endoscopic camera to look at these joints. Looks like for the most part whatever rework was done to replace these chips was done very poorly. This wouldn't meet even 1GHz standards, let alone 6GHz. I'm crossing my fingers that this needs a reflow of some type, and maybe some additional solder.Note:For HF standards, my understanding is that the process must be done accordingly:1. Provide minimal solder paste on each RF pad and ground. Solder must cover the entire pad evenly.2. Properly seat all components against pads within 100um accuracy. Confirm evenness in XYZ.3. Reflow solder in an oven4. Confirm with microscope the solder joint. Test each joint with a multimeter in case of cold solder joints. Joint must be less than .2ohm impedance. Look for any unevenness in the solder joint.5. Add additional solder if impedance test fails.6. Wash away flux with ipa. Confirm removal of flux7. Check on VNA for S11, calibrated to 50 ohms. Confirm minimal reflections across qualified band.It doesn't seem to meet these standards at all.Input 1 (Which works for a 1KHz AC signal):Apologies for the shaky cam.Note the uneven flow on these joints. That's going to cause a bunch of reflections at anything near RF.Same here but for the shield of the connection.Uneven flow, clear cold solder jointThis connection might be all right, hard to tell. I also don't know where the guard traces are connected to.Input 2Note the contaminants in the solder. Too much solder on the input too.Minimal jointing on the input connectionZero jointing on the ground/power connectionsMinimal jointing again. I'm willing to bet they didn't remove the shield when they replaced these attenuators, so the iron couldn't fit.Barely acceptable jointing on the outputs.I think you get the idea. Combined with the leftover flux, I'd say someone tried to do a rework and then couldn't get it to work--so they tossed the whole thing. I have a pretty thin iron, and some qtips with ipa that can clean up this flux. Hopefully that'll restore the attenuators to their former glory. If not I'll post an update after I cry and pay the $900 to replace them.

author: sj_phz
author_rank: Newbie
timestamp: July 11, 2025, 09:06:41 pm
content: Update: Channel 4 works now after reflowing. There is still a clear grounding issue on it though (I'm picking up 60Hz noise all over) but I think a reflow on the input ground lead will solve that. Will update this post if I can get 2 and 3 working the same way.