HP 54501A--is it worth it? - Page 1
Forum section: electronics / testgear

author: GreyWoolfe
author_rank: Unknown
timestamp: August 31, 2015, 09:19:53 pm
content: A local surplus store has a HP 54501A for $40. It is marked that the power supply needs repair. It is unknown if there is anything else wrong with it. Is it worth trying to repair if nothing else but to gain some troubleshooting skills? I do have another scope to help troubleshoot if needed.

author: JackP
author_rank: Regular Contributor
timestamp: August 31, 2015, 10:27:19 pm
content: I'd say yes. Good quality insides, should fun to repair (and hopefully easy if it's a PSU problem). Check for things like screen burn, maybe check if the RAM is the older battery backed, or newer NVRAM if you can. Only 1MHz realtime BW, but 100MHz ETS can be useful in SOME applications (no flaming please). I'd love it for that money, especially with no shipping, as it is HUGE.

author: mos6502
author_rank: Frequent Contributor
timestamp: August 31, 2015, 10:39:29 pm
content: 10MS/s and 500 (five hundred) memory points is pretty much a joke. Usability is probably pretty horrible due to the single rotary knob.I see even a working one has been sold on eBay for $50 (plus $94 shipping, though).

author: JackP
author_rank: Regular Contributor
timestamp: August 31, 2015, 10:49:53 pm
content: He said he would do it just for the troubleshooting skills. I think it quite nicely balances old and new, and has some nice DIP construction. $40 will get him a great insight into design of that era, and provide a valuable learning resource. Maybe buy it, repair it, and then flip it for maybe 10-20 bucks more, or donate it, or keep it for when it does come in useful. I agree, it will suck for a daily driver in this era, though, but that isn't really his reasoning for this purchase (from what I've inferred, we can await his actual thoughts).

author: DimitriP
author_rank: Super Contributor
timestamp: August 31, 2015, 10:58:27 pm
content: Quote from: GreyWoolfe on August 31, 2015, 09:19:53 pmFor $40 it would be hard to resist, if not just for the satisfaction of getting it working again !It all depends on what you were planning to do with the forty bucks if you didn't spend it on the 'scope

author: GreyWoolfe
author_rank: Unknown
timestamp: September 01, 2015, 12:16:52 am
content: Quote from: JackP on August 31, 2015, 10:49:53 pmIt wouldn't be a daily driver. I have a hacked Hantek DSO5102B and a Tek 2235. If I get it, I would just like to see if I can fix it on the cheap and maybe donate it to someone in my ham radio club. I am just looking to get some troubleshooting experience with the help of the EEVBloggers of courseDimitriP, I'm sure that I could waste the money on something else but I think that this just might be fun.I might just keep it as it will give me on screen measurements that the 2235 won't. We will see. If I do decide to get it, it will probably show up in the repair thread.

author: vk6zgo
author_rank: Super Contributor
timestamp: September 01, 2015, 01:38:14 am
content: Quote from: JackP on August 31, 2015, 10:49:53 pmOr any era----this generation of device is what put people off DSOs back in the 1980s/90s.They obviously had many specific uses,but as a general purpose workshop 'scope,they were severely lacking.

author: Muxr
author_rank: Super Contributor
timestamp: September 01, 2015, 01:55:12 am
content: For what it's worth it's not the same thing but I have a 54610B, which while a newer model is I think pretty similar in terms of usability.I just love using it for some reason. The UI is really well thought out, and it's surprisingly responsive for an old DSO. I find I use it more often than my Rigol DS2000.I use it for when I just need to check a signal real quick. It boots fairly quickly and the auto-scale and auto-trigger seem to just work. So it's perfect for if you just need to take a peek at some repetitive signals. I can be done identifying a signal with it in half the time it takes me to do it on the Rigol.If you think you can fix it fairly easily, I think it might be worth it for $40.

author: lowimpedance
author_rank: Super Contributor
timestamp: September 01, 2015, 04:31:34 am
content: A switch mode power unit that was outsourced by HP and for which no schematics (that I am aware off) exist, or for the rest of the instrument either. !.Only very basic flow chart type service info in the manual.Its quite densely packed in with metal shielding throughout which makes it a pain to get down to the components etc. However the usual sources of failure are the electro's.Leakage will need to be very well cleaned before replacements are put back in. Also check for lead damage and bad joints if any caps have leaked.Try to bargain down some more since there is a good chance you will be spending more than $40 bucks.

author: Smith
author_rank: Frequent Contributor
timestamp: September 01, 2015, 05:15:40 am
content: There is a schematic (reverse engineered) of the PSU which is 99% correct. It is a pain to repair, I managed to repair mine, but I heared of lots who failed.I have the 2ch 100/400MHz 54502A. It has 6bit resolution, almost no memory, the psu is a pain in the ass, the nvram battery normally needs to be replaced after 20+ years. The fan will keep your neighbours awake. Luckely mine does 100MHz in single shot mode, unlike yours.The interface is totally different than others. Although its old slow and useless in some applications I still like the thing. It's cool, retro, HP. Its fast to boot, some settings and measurements are just so easy to do via the keypad.Yours will be usable for repetitive signals, but as I remember it took 8 samples for a full screen. So it's unusable for any serious digital debugging.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: September 01, 2015, 05:29:01 am
content: Quote from: GreyWoolfe on August 31, 2015, 09:19:53 pmAs others have said the 54501A has pretty poor specs, but IMHO it's still a very interesting scope if only for the unique single knob operation. Back in the days my main scope was a 54510A (the 250MHz 1GSa/s 14kpts version of the 54501A) and I loved it.Weak points in these scopes were the power supplies, which are industrial units made by a company which these days belongs to Eaton, and which were prone to failure. These days people often just replace it with another industrial PSU which delivers the same voltages and currents.Plus, after all these years, the mains input filter (made by Schaffner) should be replaced, as they are prone to bursting and spreading black gunk all over your scopes innards. New replacements (don't buy old stock!) are still available and cost you roughly the same as the scopeQuote from: lowimpedance on September 01, 2015, 04:31:34 amThey do exist, although Eaton wants some serious money for the schematics, plus as signed NDA.QuoteNot really:The only metal shielding is around the PSU, which simply slides out to the right, and it's really not as cramped as you think, especially when the PSU has been removed. The mainboard and the CRT board aren't shielded and pretty easy to get to, especially when the PSU has been removed.It's also pretty easy to remove the PSU cover and then slide the cover pack into place and put the opened up PSU on top, which allows you to work on the PSU while it's connected to the scope.Compared to many other scope designs the 545xx Series is really accessible.

author: mos6502
author_rank: Frequent Contributor
timestamp: September 01, 2015, 09:49:52 am
content: Quote from: Smith on September 01, 2015, 05:15:40 amWhat's the difficulty? Usually, SMPSs are really trivial to repair. Of course, if it uses some kind of super special IC that is broken, you're out of luck. But otherwise, I kind of enjoy fixing SMPSs, because they're so easy to repair.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: September 01, 2015, 10:10:06 am
content: Quote from: mos6502 on September 01, 2015, 09:49:52 amIt's been a while since I had one but if I remember right these PSUs were a bit more complex, with various crude interconnected monitoring circuits for all kinds of stuff. I believe many people ended up simply bypassing the defective circuitry.QuoteMaybe you should consider turning this into a business (i.e. offering a PSU repair service), you could make serious money that way.

author: mos6502
author_rank: Frequent Contributor
timestamp: September 01, 2015, 11:06:57 am
content: Quote from: Wuerstchenhund on September 01, 2015, 10:10:06 amSo, more complex than the average ATX PSU? I mean, those have overcurrent and overvoltage/undervoltage monitoring, too.Quote from: Wuerstchenhund on September 01, 2015, 10:10:06 amI'm assuming those would be highly specialized/industrial PSUs? I don't think it would make sense having someone fix your average $50 Meanwell PSU.Do you have something specific in mind? Drop me a PM if you want to talk business, I've fixed stuff for money before.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: September 01, 2015, 12:19:11 pm
content: Quote from: mos6502 on September 01, 2015, 11:06:57 amAs I said it's been a while so I'm talking from memory but if I remember right these PSUs had a somewhat strange design with several interconnected monitoring cicuits (more complex than your average ATX PSU), and the odd way some of those were designed didn't help.QuoteYes, I'm talking about PSUs like the one in these scopes, or any other industrial/proprietary type of PSU. These days I'd say an ATX PSU isn't even worth openingQuoteNot at the moment, but there were quite a few occurrences were I could have used a somewhat reasonably prices (i.e. not €200/hr) repair service. The thing (for me at least) is that my home lab is limited equipment-wise and pretty small, plus these days I rarely work on SMPS designs any more, which means I'd not only have to get the neceesary tools, it would also very likely take me much longer to figure out what's wrong than someone who fixes SMPSes on a more or less regular basis. So in some cases I'd rather send it off and pay someone to fix it than having it sitting on my bench for weeks waiting for my attention (and preventing me from working on my RF designs).But I'll definitely keep you in mind

author: Smith
author_rank: Frequent Contributor
timestamp: September 01, 2015, 05:40:46 pm
content: Let's go back on topic: Yes, buy it, it's cool.I've seen people replace the PSU with other types, shouldn't be a real showstopper. The rest is quite easy to work with. Just a few screws opens up the case, and only 2 plastic pins keep the PSU in it's place. All other PCB's are hold on place with a few screws.

author: Macbeth
author_rank: Super Contributor
timestamp: September 01, 2015, 06:27:37 pm
content: Totally buy it. Back in 1989 my first scope was aTelequipment D52I got for £25 which is probably a lot more than $40 considering inflation. It was faulty (wouldn't trigger). I got a copy of the service manual from one of the technicians at my college, photocopied it, and proceeded to diagnose the circuit for faults. Interesting working with valves and germanium diodes! I isolated the fault using the scope probes on itself! Got it working by changing a big fat unobtainium germanium diode for a 1N4148. That scope served me well despite how poor it was. I gave it away to a tinkerer friend 5 years ago. Fixing stuff is fun!

author: GreyWoolfe
author_rank: Unknown
timestamp: September 01, 2015, 09:34:31 pm
content: I found the service manual so the next time I am in the neighborhood, I will see if it is still available. If nothing else, if I can fix it, it will do the same as my Tek 2235 but with onscreen cursors and measurements.

author: lowimpedance
author_rank: Super Contributor
timestamp: September 02, 2015, 12:25:51 am
content: Just remember the service manual will be of limited use (HP wanted you to send it back for repair!). However you seem ready to have a crack at it. So start a repair thread when you get it so we can all have a good look at the guts of it (PSU that is). It would seem info and those here with the skills to help are available.

author: Stray Electron
author_rank: Super Contributor
timestamp: September 04, 2015, 07:43:09 pm
content: Does anyone if this PSU will interchange with any of the other HP 54xxx series scopes? I seem to remember that the PSUs from one of this series was also used in another piece of HP gear but I can't recall what it was.FWW I have a working HP 54510A and I really like it, even though I have "better" scopes.