Help needed to find why HP 54510A oscilloscope won't boot or stay on

[sebth]

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

[singapol]

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.pdf

The front panel:
http://cp.literature.agilent.com/litweb/pdf/54510-90901.pdf

[sebth]

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 ?

[sebth]

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 ?

[Stray Electron]

  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.

[sebth]

I found 2 socketed ICs and reseated them both. It did not fix it for me.

[tautech]

  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.

I found 2 socketed ICs and reseated them both. It did not fix it for me.

Remove all inter-connects, inspect, clean if necessary and re-seat.

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 ?

Failure codes should be in the Service manual.

[sebth]

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.

[tautech]

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.

With that knowledge, I'd be checking the PSU is to spec; voltages correct and ripple levels as specified.

[poot36]

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.

[Smith]

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.

[sebth]

I checked the power supply using the service manual posted by singapol at http://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.

[Daxxin]

Much better if you replace power supply caps too low voltages rails level can reboot the scope 

[poot36]

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.

[singapol]

I checked the power supply using the service manual posted by singapol at http://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.

You 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.

[sebth]

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 ?

[Stray Electron]

"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!

[sebth]

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 ?

[wn1fju]

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.pdf  is someone's attempt at reverse engineering the schematic.

[PaulAm]

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.pdf  is someone's attempt at reverse engineering the schematic.

+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.

[singapol]

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

[sebth]

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 ?

[singapol]

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 ?

It's to prevent tampering and proof of calibration/setting during production process. Also could be for waranty issues to prove it has been tampered?

[sebth]

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.

[singapol]

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.

A trimpot is basically a resistor with a center tap to vary the ratio of both halves like a fixed voltage divider
with 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.