Help needed on HP 54601A oscilloscope display problem.(SOLVED)

[JacquesBBB]

Dear All,
I have scavenged an HP 54601A scope which I will be trying to restore to full working order.

As you see, there is a display problem.

I will be looking to the power supply soon, but

Does any one have a  hint on where the vertical problem of the display comes from ?
Lettes  are also inverted.

Thanks !

[KJDS]

It's one of two caps on the display driver board. From memory one is 1000uF and the other is either a 22 or 16uF cap.

Either can cause the issue, it's easiest just to change both. From memory I don't think the schematic was available, but if you find it and post it up then I should be able to highlight the caps. If not then a photo of the board may jog my memory.

[JacquesBBB]

Thanks KJDS,

Meanwhile, I  found  also this post on the keysight site
where the problem is discussed.

http://www.keysight.com/owc_discussions/thread.jspa?threadID=17356&start=15&tstart=-1

All the schematics are also available on the site at
http://www.keysight.com/main/editorial.jspx?cc=FR&lc=fre&ckey=1517718&nid=-536900196.536898053.00&id=1517718

I attach here the Display schematics. I will try now to change these caps.

[KJDS]

That's close to what I remember, but I suspect I did a different scope in the series. I suspect that changing all the electrolytics round IC 601 will cure the problem. If you've not got an ESR meter then that's the easy way forwards.

[JacquesBBB]

All the  voltages of the power supply were right inside the spec intervall.

A rubber pad had decomposed, and this is something I already saw on another
HP 54601A that I fixed not so long ago.

I look for the bad caps which were supposed to be C608 and C609.
I desoldered both. C609 (1000 uF) was OK : 876 uF , 0.68 ohm ESR.
While C608 (10uF , 16V) was damaged (not even readable on the ESR meter).
See the picture.

I inspected the other caps, but they looked OK, so I left them on place.
Of course, I could have changed everything,  but the other caps were 100V , and
I suspect that C608 was  too low voltage for its task. I replaced it with a 100V, 10 uF cap.

C608 and C609 are the two caps that are under the date on the attached picture.

After that, and a little bit of calibration, everything is working fine, like magic
(sorry for the fuzzy pic).
I spend more time then changing the fan, as the original one made a terrible sound,
but I had to adapt the new fan to fit in place.


Thanks again KJDS

[JacquesBBB]

And the global picture

[GreyWoolfe]

Glad the repair turned out to be simple.  Now it is time to enjoy the scope.  Take care of it so you don't 

[R Lamparter]

Another successful repair using this information.  Only the small 10 uf capacitor, C608 on the video board tested bad (abt 7 uf and v high ESR).  Replacing that fixed the problem.  Before and after photos attached.

[Bushougoma]

This is a common issue on CRT TVs based on the symptoms and value of the cap I would say that was the vertical pump up capacitor.

It's often the repair for compressed vertical deflection. I try not to think about how many CRTs were disposed of because of a single bad capacitor.