User Name Stay logged in? HP A - Any familiar with it? Hi all, Just picked up a HP A. Boots, ran all the tests in the service manual. Can look at signals etc.
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Welcome, Guest. Please login or register. Did you miss your activation email? This topic This board Entire forum Google Bing. Print Search. Cubdriver Supporter Posts: Country: Nixie addict. I snared this little beastie from the 'bay; it arrived today. It was advertised as 'For parts or not working', with a note that it wouldn't power up and that the fuse was good.
For the price, I figured it was worth a shot: As noted, it doesn't power up - plug it in, press the power switch and from all external appearances, a whole lot of nothing happens. No lights, no cooling fan, no nothing. As advertised, the fuse checked out as good. Externally, it looks almost brand new - the front panel is in beautiful condition, and other than a missing HP emblem on the carrying handle and a bent fan filter retaining screw it looks great.
The missing emblem makes no difference to me, and the bent fan retainer was fixed in about 30 seconds with some gentle persuasion from a pair of lineman's pliers. This is as it came out of the box - no cleaning: Removing the top cover cake - 4 captive quarter-turn fasteners and off it came, with no loose hardware to lose reveals the usual solid construction typical of HP instrumentation. There is beryllium copper fingerstock along the sides and top to bond the cover to the chassis, and the boards are further shielded with sheet metal covers: This was a surprise - I was expecting a long electrostatically deflected CRT like what you find in a scope; instead it has a short little magnetically deflected one.
It's so cute. I wonder, if you feed it, will it get bigger? It's protected by a sheet of Plexiglas, not readily evident at a glance in the photo: Removing a metal cover exposed the power supply section: Linear regulators on the main board.
I suspect that the blue electrolytics on the removable card immediately above them are the filters: The initial troubleshooting procedure I found in the manual on Keysight's site began with checking a pair of 12V bias supplies, which were operational and within spec.
The lighted one shown indicates an overcurrent fault. That fault was then isolated to the main part of the instrument by pulling the board out of the edge connector to disconnect it from the array of linear regulators on the mainboard it feeds them.
When power was reapplied, the overload LED was off. This came as no great surprise. Of course THAT troubleshooting sequence is in part II of the manual, which is not readily available online as a PDF that I've found, so further misadventures in troubleshooting will have to wait a bit until I get my hands on a hard copy of the two volume troubleshooting and repair manual.
Off to evilBay If it jams, force it. If it breaks, you needed a new one anyway Wow great score! Beautiful condition, hopefully it can get fixed! Vgkid Super Contributor Posts: Country:. If you own any North Hills Electronics gear, message me. Love that attention to detail, keep the photos coming, is this thread better in the "Repair" listing? Watch where that landed we might need it later.
The following users thanked this post: shakalnokturn. Good to see it was complete, nice construction as usual. Keep us posted on what you find. If it were me I would go on with troubleshooting for as far as I could get without the second half of the troubleshooting guide.
Being HP, I would guess a shorted tantalum capacitor, probably on one of the 15V rails. Replace with a 35V part, and for good measure look on the board for all the relatives and do them as well on that rail and other highish voltage rails. My hope is that it will turn out to be a shorted cap on one of the rails, too, at which point I'll likely shotgun similar ones too to try to head off the next one crapping out and causing grief.
I expect to order a copy of the two volume service manual later today, but in the meantime will perhaps poke about further at it tonight. Troubleshooting is complicated a bit by the fact that the instrument's schematics are contained in the volume of the repair guide that I don't have access to and of course the scanned versions would likely be fuzzy and frustrating to read anyway.
In hindsight, yes, this probably should go in the 'repair' section. I'll see if I can have it moved. My 2 cents : one of the two TO-3 regulators is dead. They conk out and the circuitry behind gets to eat unregulated power so it overloads. Professional Electron Wrangler. Any comments, or points of view expressed, are my own and not endorsed , induced or compensated by my employer s. Did a touch more troubleshooting tonight, and also ordered a copy of the service manual both parts.
Whatever ails it seems to be in the main body of the instrument - I pulled all but the power supply cards and it still indicates the overload.
I made some resistance measurements in the vicinity of the row of linear regulators, and found one tantalum cap that seemed a bit suspicious 29 ohms where one other was in the neighborhood of ohms, and the rest well north of that.
It's the one on the bottom right of this picture, next to the CR silkscreen. Lifting one side of it was no help; it appears to be fine and even with it out of the circuit I still had my overload. I then noticed that a big electrolytic on the backplane board smack in the middle of the power supply it lives between the two power supply cards when they're plugged in looks a bit lumpy near the bottom. That'll be the next thing to investigate when I get more time.
It's barely visible at the top edge of this image, slightly to the left of center. They put a seriously physically huge microprocessor chip in this thing. Apparently they needed a lot of pins, so they just made a huge DIP to encase it. From what I've learned online, it appears to be a custom labeled Motorola MCL; a 32 bit processor with a 16 bit bus. It looks like a supercarrier sailing among a fleet of frigates.
Nice machine, I also have one. What makes the HPA special is the optional usage of magnetic bubble memory that was offered as an option option - my unit has that option , with that memory option a A can store waveforms.
Bubble memory is a non volatile memory technology of the eighties that was going to be a big thing before the advant of flash memory technologies. Well, the A is the only test equiment model HP used bubble memory in, guess it was not that great.
The fault in your unit is most likely a shorted tantalum, unfortunately there a quit a of these caps that can go bad. After weeks of procrastination, laziness, lack of time due to business travel and generally having too much on my plate, I finally got around to digging further into this now that I have both volumes of the service manual. It's an HP specs according to the manual are diode, switching, 80V, mA, 2nS recovery, DO package ; according to what I found online it crosses to a 1N which seems to have slightly different specs, but as it's a rectifier I can't imagine that it's super critical.
Since I don't have any 1Ns kicking around, I installed a 1N in its place for the time being to check things out. The replacement rectifier brought it to life immediately. I plan to get the proper replacement on order shortly, and will then wring it out and see if there are any other issues. The failed diode and its location in the circuit: A detail of the cleverly disguised short circuit: The 'temporary' fix installed CR will likely be changed, too, as it's gotten a bit toasty; its location is not shown in the schematic image, but it's the top right diode of the bridge, directly above CR, and was likely loaded by CR as it was failing : Amazingly, with the power supply once again doing its thing, the instrument comes to life: And finally a detail of the display: I'll dig into it further once I get the proper part installed, and post some more detailed images of the various boards and whatnot as I go through it.
It's an impressive little box, with a lot of stuff packed inside. I don't recall if I mentioned this earlier, but based on the serial number it appears to be a late manufactured unit. Fantastic, congrats! I have one of these as well - it's throwing an error on boot, but the error is only listed in Volume 2 of the manual, which isn't available online - I'm trying to get my hands on a paper copy, but it's pretty rare Haven't gotten to that point yet, too many other projects.
What error is it throwing? Perhaps I can look it up and try to at least point you in the right direction. Quote from: Cubdriver on February 18, , pm.
R and C are in series and form a snubber network across the 5V supply windings of T It's a center-tapped full wave bridge setup shades of an old vacuum tube circuit. If 2 was shorted to the resistor, it would have been either a dead short to one end of the winding, or, at best, 22 ohms based on R's value.
Separating them would be a good start. The resistor should be 22 ohms; the cap you won't be able to measure without lifting one side as it will be in series with the resistor and the transformer secondary winding. Hope this helps a bit. The full wave rectifier for that 5V supply is CR; that's the TO-3 packaged device on the heat sink above the transformer. It's a common cathode rectifier; I assume the pins are the anodes and the case is the cathode, but don't presently have the energy to dig out and open the A to check.
Perhaps tomorrow, if it's necessary. Quote from: Cubdriver on February 20, , am. C is a fairly large cap, but the markings are oriented so I can't read them of course. It seems like it might be too low for such a large cap. That might explain why R got hot, I'd have to check the schematics which I don't yet have. Also, I double checked the two white wires, I don't think wire '1' shorted.
It doesn't seem to have burned through the insulation, just charred the insulation. Also the wire was only touching the resistor 'jacket' not the bare leg. Testing them in circuit gives me 18 kohms on both. I'll have to check where they go when I get the schematics. But right now, I think the 5v rectifier has gone south Forgot to mention, I re-installed the 5v board, same issue.
HP 3561A Dynamic Signal Analyzer With OPT 001
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