Help needed to find why HP 54510A oscilloscope won't boot or stay on - Page 1
Forum section: electronics / repair

author: sebth
author_rank: Contributor
timestamp: September 26, 2015, 05:22:04 pm
content: Hi everyone,I'm just starting to learn electronics as a hobby so I need all the help I can get.I recently bought an HP 54510A oscilloscope from Kijiji. The guy had it powered up and plugged on the calibrator output on the back to show me it was working. We talked for a couple of minutes while the scope was powered on and everything seemed fine.When I got home, I started to follow the Getting Started Guide. First step was to "Resetting the instrument". Press the RECALL and CLEAR key. I guess that's a kind of factory defaults. Then it said to plug the probe to the ac calibrator output and press AUTOSCALE. Nothing happend, so I decided to reboot the scope and try again. That's when the problems started.Now most of the time I can't see anything on the screen when I power it up. Sometimes the fan is stuck in a loop where it stops and starts again at about 1 second interval. A couple of times the screen came up, but it stopped after about 1 minute or less.Can anyone help me in finding, and possibly fixing the problem ?Thank you

author: singapol
author_rank: Frequent Contributor
timestamp: September 26, 2015, 05:49:31 pm
content: Sorry to hear, maybe you are better off with an analog scope but since you got this hp scope...A previous thread might help...It could be the emi filter (shafner brand) could have failed.PS you may wish you had not got this type of digital scope given the replacements you have to do.https://www.eevblog.com/forum/repair/hp-54501a-troubleshooting-repair/The service manual:http://cp.literature.agilent.com/litweb/pdf/54510-90903.pdfThe front panel:http://cp.literature.agilent.com/litweb/pdf/54510-90901.pdf

author: sebth
author_rank: Contributor
timestamp: September 26, 2015, 05:57:04 pm
content: Thanks for the reply. I'll have a look at the link.It's really hard to find what is a good scope or not for a beginner. I spend a lot of hours reading about it but I never had a clear picture of what was good or not for me. This one seemed "ok" from what I understood and was not very expensive.I find it weird that it stayed powered on a couple of minutes when the seller showed it to me but now it can stay up more than a minute for me. Is was hoping it could have something to do with the factory reset I did instead of a hardware problem, I guess it's just coincidence ?

author: sebth
author_rank: Contributor
timestamp: September 26, 2015, 06:33:31 pm
content: I noticed an other thing. When the screen does light up, sometimes I get an error message saying something like "Failed interpolar cal" . Any idea what that means ?

author: Stray Electron
author_rank: Super Contributor
timestamp: September 26, 2015, 06:52:06 pm
content: I have the same model and it failed to boot and I opened it up and reseated one of the socketed ICs and it's worked fine ever since.

author: sebth
author_rank: Contributor
timestamp: September 26, 2015, 07:19:20 pm
content: I found 2 socketed ICs and reseated them both. It did not fix it for me.

author: tautech
author_rank: Super Contributor
timestamp: September 26, 2015, 07:49:13 pm
content: Quote from: Stray Electron on September 26, 2015, 06:52:06 pmQuote from: sebth on September 26, 2015, 07:19:20 pmRemove all inter-connects, inspect, clean if necessary and re-seat.Quote from: sebth on September 26, 2015, 06:33:31 pmFailure codes should be in the Service manual.

author: sebth
author_rank: Contributor
timestamp: September 26, 2015, 10:31:37 pm
content: I unplugged and cleaned everything I could, still no luck.An other detail I found out, if that can help to identify the problem : If I leave it off for some time, it will turn on an work for a 30 to 60 seconds. After that, it won't turn on at all, the fan will do the stop and start that I mentioned in the first post, etc.. If I leave it off for an hour, it will work for an other 30 to 60 seconds.

author: tautech
author_rank: Super Contributor
timestamp: September 27, 2015, 01:19:22 am
content: Quote from: sebth on September 26, 2015, 10:31:37 pmWith that knowledge, I'd be checking the PSU is to spec; voltages correct and ripple levels as specified.

author: poot36
author_rank: Frequent Contributor
timestamp: September 27, 2015, 05:47:14 am
content: It could also be a bad solder joint that when warm it fails. When you took the scope home did it experience any vibration or other shock? This could have caused a almost bad solder joint to go bad.

author: Smith
author_rank: Frequent Contributor
timestamp: September 27, 2015, 06:38:30 am
content: Solder joint are the first thing that comes up indeed (after traveling). Just take out the pcb's and check all solderjoints for cracks. You might want to start with every solderjoint that experiences pressure from other pcb's and cables. Sometimes it helps to use a bright light and gently wigle the connector.While you are at it you might want to check other components visually, and especially caps.

author: sebth
author_rank: Contributor
timestamp: September 27, 2015, 04:09:32 pm
content: I checked the power supply using the service manual posted by singapol athttp://cp.literature.agilent.com/litweb/pdf/54510-90903.pdf.Using page 6-21 (page 111 of the PDF) I did the first test "Supply Loaded". The test point that is supposed to be -12V is around -9V. The others are ok (except when the unit reboots on it's own, the power drops and comes back up again to the correct value). Is that test alone enough to know the power supply if faulty or do I need to do the "Supply isolated" test also. I guess I need to do it but since I don't have a 2-ohms 25 watt resistor I figured I'll ask first.I also checked the solder joints and caps and nothing seems wrong. I will check more thoroughly if the problem is not with the power supply.

author: Daxxin
author_rank: Regular Contributor
timestamp: September 27, 2015, 05:05:53 pm
content: Much better if you replace power supply caps too low voltages rails level can reboot the scope

author: poot36
author_rank: Frequent Contributor
timestamp: September 27, 2015, 06:06:27 pm
content: Check all of the power supply voltages for ripple as well. Use your multimeter on AC volts and if you see more then 250mV on the meter you may have a problem or your meter is not capable of testing in this fashion (if your meter shows over 1 volt it probably won't work for this test). Also figure out why the -12V line is at -9V, that is a major problem and is most likely the cause of the error message you are getting.

author: singapol
author_rank: Frequent Contributor
timestamp: September 27, 2015, 06:38:18 pm
content: Quote from: sebth on September 27, 2015, 04:09:32 pmYou have already found a -12V descrepancy, unplug W1 to main assembly ( mains power switch off) turn on power switch and check -12V again. Now that it's unloaded it should measure -12V or higher. If it's still -9V the problem is in the switchmode supply.

author: sebth
author_rank: Contributor
timestamp: September 28, 2015, 01:21:19 pm
content: I checked with W1 unplugged and the voltage is still wrong.I also tried to check for ripple as poot36 suggested but my meter showed values moving from 0 to 40 volts.I checked online for a replacement power supply but they seem to be rare and a little bit too pricey for me. Is it realistic for a beginner to try to fix this ?

author: Stray Electron
author_rank: Super Contributor
timestamp: September 28, 2015, 01:40:11 pm
content: "I checked with W1 unplugged and the voltage is still wrong.I also tried to check for ripple as poot36 suggested but my meter showed values moving from 0 to 40 volts.I checked online for a replacement power supply but they seem to be rare and a little bit too pricey for me. Is it realistic for a beginner to try to fix this ?"Some of the switch mode power supplies NEED a load in order to regulate properly.Does your meter have an AC mode? Use that, it will read the ripple voltage directly.Yes, it's worth a shot. Excessive ripple due to bad caps is a COMMON problem and relatively easy to troubleshoot. Problems like this are how beginners get to be experts!

author: sebth
author_rank: Contributor
timestamp: September 28, 2015, 02:08:42 pm
content: I tried on AC mode and that's when I got to 0 to 40V values. In his post poot36 suggested that if I read a value that is more that 1 volt I probably can't use my meter for this test. I'll try to find a beter meter.The service guide suggests to use a 2 ohms 25 watt resistor as a load to test the PSU when it is disconnected from the main board. I don't have a 25W resistor right now that's why I haven't tried it yet.I attached a picture of the power supply. Do you see anything wrong just by looking at it ? I noticed white stuff on the inductors in the lower right, is that normal ?

author: wn1fju
author_rank: Frequent Contributor
timestamp: September 28, 2015, 03:02:11 pm
content: Look VERY carefully with a high powered flashlight around the base of all the electrolytic capacitors. You are looking for any electrolyte seepage which may be clear or white (if it has dried). Also look at the little control board (top right of your picture, out of view) for any burnt parts. Also look for any seepage that bridges traces.These are Boeschert supplies used in a lot of HP scopes. Sometimes you will see one on eBay for <$100. Sometimes it is cheaper to buy the entire HP piece and throw everything away except the power supply. They were used in HP 5450x scopes, 1650 logic analyzers, and a lot more.http://www.radiocollection.be/images/restaurations_img/HP54503/supplyHP54503.pdfis someone's attempt at reverse engineering the schematic.

author: PaulAm
author_rank: Frequent Contributor
timestamp: September 28, 2015, 05:12:24 pm
content: Quote from: wn1fju on September 28, 2015, 03:02:11 pm+1 on that. I had one of those PS die on a logic analyzer that was going to a friend and it was cheaper to buy another LA for the PS than just a replacement PS (I didn't have time to troubleshoot it).You can also use an ESR meter to track down bad caps. Or, just shotgun all of them. They're old enough to make that worthwhile.

author: singapol
author_rank: Frequent Contributor
timestamp: September 28, 2015, 05:44:24 pm
content: Since you said -12V measured only -9V, I would suggest you trace the regulator circuit A8. You can adjust R58 to see if voltage can go to -12V or not. It could be LM350 is bad. Check the caps too. See page 2 and 3 of the link provided.http://www.radiocollection.be/images/restaurations_img/HP54503/supplyHP54503.pdf

author: sebth
author_rank: Contributor
timestamp: September 28, 2015, 10:42:10 pm
content: Thank you all for your answers. I'll try everything you said, it will probably take me a couple of days.This lead me to an other question : When are the adjustments trim pot supposed to be used ? Mine were glued so I suppose it's not something that is normally changed, maybe only after a repair ?

author: singapol
author_rank: Frequent Contributor
timestamp: September 29, 2015, 02:56:13 am
content: Quote from: sebth on September 28, 2015, 10:42:10 pmIt's to prevent tampering and proof of calibration/setting during production process. Also could be for waranty issues to prove it has been tampered?

author: sebth
author_rank: Contributor
timestamp: September 29, 2015, 03:05:42 am
content: That's what I thought about the glue. I was wondering about the trim pot itself though. Why do we need it instead of a regular resistor? I guess it's because each component have a slightly different value so we need to adjust that when we change some components.

author: singapol
author_rank: Frequent Contributor
timestamp: September 29, 2015, 03:15:16 am
content: Quote from: sebth on September 29, 2015, 03:05:42 amA trimpot is basically a resistor with a center tap to vary the ratio of both halves like a fixed voltage dividerwith 2 resistors and you tap the common end for your required voltage with respect to ground but you need to calculate this resistor ratio. A trimpot simplfy this. It's cheap and convenient/fast.

author: sebth
author_rank: Contributor
timestamp: September 29, 2015, 02:00:33 pm
content: Quote from: singapol on September 29, 2015, 03:15:16 amIn this particular circuit thought, the power supply, why do we need adjustment instead of a fixed value resistor ? Is this something that needs to be adjusted from time to time in a power supply or it's only adjusted when the PSU is built (or when we changed other components in it ?).

author: singapol
author_rank: Frequent Contributor
timestamp: September 29, 2015, 05:46:08 pm
content: Quote from: sebth on September 29, 2015, 02:00:33 pmReal world components like resistor's resistance will drift with temperature and time/aging so you needto recalculate the new resistors to put in but with a potentiometer all you need is just turn the pot until thevalue/resistance corelate to the required voltage. Although overall they will remain in tolerance over the years. It's just convenient for maintenance.

author: sebth
author_rank: Contributor
timestamp: September 30, 2015, 01:18:23 pm
content: I tried the trimpot and the voltages goes from -8.5V to about -10V .I also looked for cracked joints, busted caps, residue on the board, etc... but didn't find anything.I guess my next step is to replace all the caps like others have suggested.

author: cncjerry
author_rank: Unknown
timestamp: September 30, 2015, 03:02:13 pm
content: If an active component in a switch mode power supply fails, the output is zero. As another poster mentioned, they operate as an oscillator and without a load to drag the voltage down, they won't generate the upward swing. So you'll see no output without a load, and that load could be internal to the power supply, or with a failed active component (as well as inactive) but I point this out since you have output. This means that though it has an incorrect level, it is unlikely to be an active component which points at capacitors, most likely, or a resistor that changed value. The resistors would be easy to check, but save yourself some time and swap out the caps.If you can put a constant load on the PS that would eliminate the downstream electronics. If you are worried about putting more money into the scope, then wire up some resistors and load the supply.

author: vk6zgo
author_rank: Super Contributor
timestamp: September 30, 2015, 03:18:15 pm
content: Quote from: cncjerry on September 30, 2015, 03:02:13 pmQuite a few switchmode supplies will run without a load,notably,those on Sony CRT TV sets.The old Philips ones will hiccup without a load,& PC supplies don't regulate properly without one.

author: sebth
author_rank: Contributor
timestamp: September 30, 2015, 04:00:07 pm
content: Quote from: cncjerry on September 30, 2015, 03:02:13 pmThe service guide mentioned using a 2 ohms 25Watts resistor as a load. I ordered one so I will try it when it arrives. If the voltages are correct using the resistor as a load, but incorrect when plugged in the main board, it would mean the problem is not in the power supply but somewhere else in the device, right ?

author: cncjerry
author_rank: Unknown
timestamp: September 30, 2015, 04:22:40 pm
content: most likely, yes, if the resistor loads the supply correctly and the voltages look good, look somewhere downstream. I suspect you will find the voltages are still off with the resistive load.

author: sebth
author_rank: Contributor
timestamp: September 30, 2015, 08:33:29 pm
content: I read somewhere that an ESR meter could be used to test for bad capacitors without removing them from the board, but I also saw comments about the fact the it can not be used when there is multiple capacitors close together.Could that help with that power supply ? I don't have an ESR meter so I would need to buy one. I was a lot of cheap ones and some expensive ones. Would something simple like that workhttp://www.ebay.ca/itm/2015-newest-version-of-inductor-capacitor-ESR-meter-DIY-MG328-multifunction-test-/111521859338?hash=item19f738870a?

author: singapol
author_rank: Frequent Contributor
timestamp: September 30, 2015, 11:22:18 pm
content: Quote from: sebth on September 30, 2015, 08:33:29 pmPennywise pound foolish. MESR100 V2 is the one to get ( only esr not multi purpose like diy), it has probe resistance zeroing feature. Get the esr/cap meter combo if you can afford it. Although if you hunt around there are cap meters that also do esr and some more but this cheapy test at 100Khz. good for switchmode power supply.Those diy ones may not test at 100Khz. and may be lower frequency like 10Khz.Or alternatively get UT139C multimeter that can test caps up to 100K uf. but not esr.PS: MESR100 V2 can test in circuit but you have to discharge the caps first with a resistor, a ceramic 1K ohm 5 watt or larger and double checked with DMM if it discharge to about 1V or less it should be safe ( big caps takes longer time,you can use smaller values as the discharge go down to speed up the time) . It does not have auto discharge like the Peak esr meter. Good practice to check cap voltage before using esr meter.http://www.ebay.com/bhp/mesr-100

author: vk6zgo
author_rank: Super Contributor
timestamp: October 01, 2015, 01:43:24 am
content: Quote from: singapol on September 27, 2015, 06:38:18 pmsingapolhas hit the nail on the head----if everything is OK except for -12volts,that is where your problem is.If the linked "reverse engineered" schematic is correct,it isn't one of those SMPS that won't work without a load.Indeed,you have already disconnected it,& shown that is so,so don't get yourself off on a tangent.ignore all the rest of the device except the -12volt supply .This is quite a simple circuit,consisting of CR25,a flter capacitor,& the regulator,A8.In a switchmode,CR25 is probably a "fast-recovery" type,& the cap should be low ESR.If the cap dries out,the output of the circuit can look like a series of pulses,with low total energy.A DMM will often see this as a lower value of dc,as some of them don't know the difference.Sometimes "fast recovery" diodes go "a bit funny" & lose their normal characteristics,so need replacement.Other times,you will find someone has been there before you,& has fitted an ordinary power diode without the correct characteristics.

author: singapol
author_rank: Frequent Contributor
timestamp: October 01, 2015, 06:54:46 am
content: vk6zgoYou took the time to read and understand. Was wondering why OP did notcomprehend my post.All he needs to do is check the -12V circuit. Betting on LM350 but the caps could be bad too.

author: sebth
author_rank: Contributor
timestamp: October 01, 2015, 12:40:30 pm
content: I removed the LM350 on the -12V . I'll test it tonight when I get home. I don't know how to test it yet so I'll need to do a bit of research.Thank you again for taking the time to help and give advices, it's really appreciated. If I seem to ignore some of the things you say it's simply because I have so much to learn that I sometimes miss important things you said. I have the intention to re-read every post and look up everything until I understand every word though, it might just take a really long time

author: singapol
author_rank: Frequent Contributor
timestamp: October 01, 2015, 04:11:35 pm
content: There's no need to reread every post when in essence you found the problem by yourself. We just gave ahelping hand.

author: Joel_S
author_rank: Contributor
timestamp: November 05, 2015, 02:20:57 pm
content: Hello,I had the exact same problem -- the power supply would oscillate with a short "on" pulse every second or so.The root cause was leaked electrolyte from a capacitor. The leaked liquid is quickly evaporated by the airflow, but it leaves a dry, conductive residue on the board. In my case, the residue was on the voltage-setting resistors of the LM350, which kicked the LM350 output voltage out of limits and triggered the crowbar. Then the power supply would quickly restart and shot down again.The quick fix is to clean the residue with running water. When dry, the power supply works again!Of course, you still have to replace the leaking capacitor(s).I hope this helps!Joel_s

author: sebth
author_rank: Contributor
timestamp: November 10, 2015, 05:43:27 pm
content: Thanks for your reply. I did not find any sign of leak on mine, but I ordered an ESR meter so I will be able to test each capacitors.

author: vk6zgo
author_rank: Super Contributor
timestamp: November 11, 2015, 03:49:19 am
content: You have been at this for a month.You could save a lot of time & money by just replacing the capacitor in the -12v supply"on spec".The same goes for the LM350, probably the diode,& maybe the pot.If you are going to do this sort of thing for a living "down the track",you have to learn when it is more economical to use the "scattergun" approach.

author: sebth
author_rank: Contributor
timestamp: November 11, 2015, 05:12:17 am
content: Yea I know. I found an other oscilloscope that uses the same power supply for 100 CAD ( about $75 USD) so I just bought it for the PSU. I still want to fix it for the learning experience though. I'm doing this as a hobby when I have some spare time.

author: Stray Electron
author_rank: Super Contributor
timestamp: November 11, 2015, 04:09:18 pm
content: Just for future reference, what model is that?Also it might be a good idea to go ahead and try to troubleshoot the old PSU when you have time since failures of these are common, there's a good chance that your "new" could eventually fail too. And having a working one to compare to should make troubleshooting much quicker.

author: sebth
author_rank: Contributor
timestamp: November 11, 2015, 05:27:06 pm
content: Quote from: Stray Electron on November 11, 2015, 04:09:18 pmIt's an HP 54501A. The NVRAM battery is dead but other than that, it seems to be working.Quote from: Stray Electron on November 11, 2015, 04:09:18 pmYes that's a good point. It will also give me a backup PSU so I will be able to use the oscilloscope even if I did not fix the newly failed PSU.

author: Stray Electron
author_rank: Super Contributor
timestamp: November 12, 2015, 05:40:44 pm
content: Quote from: sebth on November 11, 2015, 05:27:06 pmYou can never too many oscilloscopes.

author: TAMHAN
author_rank: Frequent Contributor
timestamp: November 16, 2015, 08:53:00 pm
content: Sorry for being greedy here, arab blood kicking in. O0 O0 O0My wife designs MEAN power supplies (its her hobby). So, if you end up with a scope sans PSU which is headed to the dustbin, think about us. We would gladly pay shipping...

author: sebth
author_rank: Contributor
timestamp: November 24, 2015, 06:55:22 pm
content: Sorry TAMHAN, I'll keep it.I ended up changing all the 220uF and it's now workingFor the record, it DOES need a load to have a stable voltage. I testing with both PSU and the voltage was varying a lot for the 12V and -12V if I didn't put a load on it.Thanks everyone for your help and suggestions, it's really appreciated.

author: TAMHAN
author_rank: Frequent Contributor
timestamp: November 28, 2015, 09:21:01 pm
content: Hello,if you managed to fix it, thats great! We mainly wanted to save it from the scrap heap(We already have four scopes between the two of us. LeCroy 9354AM, Tek754D, and two Iwatsus. Plus, if I can twist the arm of my former school, a Gould OS4000).Tam