HP Agilent 54200a Oscilloscope No Image :(

[thinker1920]

Hi Everyone,

     I just got a HP Agilent 54200a oscilloscope, I was all excited plugged it in and no image . When I turn it on I hear two beeps and the fan comes on. I opened it up and did a visual inspection and didn't see anything obvious. I did notice that there was no glow in the neck of the CRT and if I'm not mistaken there should be a little heater in there. There's a test point on the power supply board and all the voltages came up within tolerance according to the service manual (they're all lower voltages 2.4v - 15v). The only thing I thought was odd was a cable that came from the power supply board that doesn't go anywhere. I checked the voltages in it and it's 120 volts AC but, it might just be a red herring.

                         Any Help would be greatly appreciated :-)

[thinker1920]

I also noticed that there's only one small ribbon cable that goes to the CRT circuit board, I just thought it strange.

[free_electron]

that's normal. those displays run off 12 volts carried on the ribbon cable.

[helius]

Can you feel static electricity on the screen? If not, the high voltage from the flyback transformer is not getting to the CRT anode.

[thinker1920]

When I went to feel for static on the screen I accidentally bumped it and the screen flashed on for a split second, Loose connection somewhere? bad relay?

[marshallh]

Unplug and replug all connectors for a start

[merox]

If you get the Scope up and running again please check out the Firmware-Version of your scope and backup the EEPROMs as soon as possible.

I got my 54200A about 2 years ago to replace my 54501A (miserable aquisition rate) and one of the EEPROMs was dead. The EEPROM just forgot its contents (not completely but it was corrupted) because of age so the Scope did not boot properly. It did it's Boot-Up-Chime but showed nothing on the screen. It took my about half a year to get "new" EEPROM files for the scope to write them to new EEPROMs, since then the scope is working fine.

Maybe you've got a newer Version with more Options, so i would be interested to get it for my Scope.

Good luck with your repair.

PS: Here are some internal shots from the scope on a german forum:
http://www.mikrocontroller.net/attachment/44967/Scope__bersicht.JPG
http://www.mikrocontroller.net/attachment/44990/Scope_Prozessor.JPG
http://www.mikrocontroller.net/attachment/44991/Scope_DAC_Speicher.JPG
http://www.mikrocontroller.net/attachment/44992/Scope_Analogteil.JPG

My thread with the EERPROM files (the thread is in german):
https://www.mikrocontroller.net/topic/293499


Edit: There is also an EPROM for the Character Generator/Screen Controller for which i have no Image. If somebody is able to make a copy if that i would appreciate an uploade of an image of that too. I would do it myself, but i have neither an EPROM reader nor an programming device.

[thinker1920]

I unplugged and replugged everything, no luck, I did measure the voltages in the cable going to the CRT board. I numbered them if looking at the cable end with the cable coming out the top of the end with the red stripe on the left side, top row 1 3 5 7 9 11 13 15, and bottom row 2 4 6 8 10 12 14 16.

1 0.72 V
2 3.3 mV
3 122.9 mV
4 3.3 mV
5 222.4 mV
6 3.3 mV
7 330 mV
8 3.3 mV
9 4.95 V
10 3.3 mV
11 12.07 V
12 3.3mV
13 383 mV
14 3.3 mV
15 388 mV
16 3.3 mV

 Not sure if that's useful info or not

[Deathwish]

Dare I suggest you get a plastic rod of some sort and gently push against the board at the rear of the tube and see if it then comes alight. if so you probably have a pin from the crt not making contact with the board or a dry / loose part on the board.

[AF6LJ]

Dare I suggest you get a plastic rod of some sort and gently push against the board at the rear of the tube and see if it then comes alight. if so you probably have a pin from the crt not making contact with the board or a dry / loose part on the board.

This is a really good suggestion, I have fixed a gob and a bunch of gear by using this to find intermittents.

[thinker1920]

I've removed the plug that connects the end of the CRT to the CRT board and plugged it back in, and I've tried lightly tapping on it with a plastic rod, and lightly pushing it while on with no luck.

  I did do some poking around and on the CRT board printed on the back it says that the pins I called 13 and 15 should give 15 V if tied together and I went back and measured it that way and I only get a mV reading. When I bumped it, it was the side that the board that connects to the CRT board is on.... I wish I could find circuit diagrams for the boards :-P

[Deathwish]

Nearest I can get for you

http://www.keysight.com/main/redirector.jspx?action=ref&cname=EDITORIAL&ckey=816900&lc=eng&cc=GB&nfr=-536900196.536898015.00

http://www.qsl.net/n9zia/test/HP54201AD_Service_Manual.pdf

http://exodus.poly.edu/~kurt/manuals/manuals/HP%20Agilent/HP%2054200A,%20D%20Operating,%20Programming%20&%20Service.pdf

http://www.helmut-singer.de/pdf/hp54200a_54200d_54201a_54201d.pdf

[thinker1920]

Thank You Deathwish!

 Awesome reference materials!

 After my last post I took the whole think apart, used an air compressor to blow the dust out and Deoxit to clean the connections, then reassembled, and got nothing but, as I was moving it the screen came on when I lifted it but, only when I lift the front right side. I then poked around a little bit more and found out if I pull up slightly on the power supply board I get the same affect.

 I'm guessing that the pin connection from the power supply board isn't making good contact, do you think I should slightly bend the pins or use something to wedge it to keep pressure on it?

[Deathwish]

I would check the PSU for dry or loose joints first, I am not into just wedging things to get them to work. Then clean the pins themselves on the connector and try again. Also get a magnifying glass and check for hair line cracks in the traces of the board. I seen enough of them causing grief in CRT tv sets in my time.

[thinker1920]

I didn't notice anything so I started reflowing the solder joints, wasn't till I got to the connector on the power supply board that plugs into the main bus that when I went to reflow one of the connections the pin fell right out, on closer inspection I saw that it and two others had hair line fractures, I removed them and soldered in some wire in there place and everything is up and running no pressure required 

  it also passed all the self tests 

 Merox how do I check the firmware and back it up?

[Deathwish]

Congratulations on fixing a fine bit of equipment.

My own starting points are : caps in psu's, look for leaks at top or legs, look for burn marks on high heat areas, cracks on such places and around any connectors, look for cracks around user inputs where such as plugs like bannana jacks are. open circuit protection resistors or fuses and such. Meh, the list could go on but I primarily look first at the above.

[tautech]

Well done OP, great when it's a simple repair. 

It's often wise just to study connections, layouts and PCB's, it can be quite surpising how easily simple faults can be found.
Good light and magnification often helps, however once I had a 6 x 4" SMD and TH PCB that had an intermittent connection and all attempts to find it failed, only a full hand reflow fixed the bloody thing. 
To this day I never found the crook joint. 

[AF6LJ]

Congratulations on finding the fault.
More often than some might think physical damage ether due to use or thermal cycling is the problem.