EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: JacquesBBB on March 07, 2015, 09:01:58 am
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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 !
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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.
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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 (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 (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.
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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.
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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
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And the global picture
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Glad the repair turned out to be simple. Now it is time to enjoy the scope. Take care of it so you don't :-BROKE
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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.
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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.