Electronics > Repair
HP 54502A repair once again
<< < (3/7) > >>
wn1fju:
You said: "I replaced all of the PSU's secondary side 220uF/50V caps. Some of them had leaked, some looked OK but
the whole batch had gone bad."

Very amusing, because those 220uF caps were exactly the ones that were leaking goo all over my PSU too!  Must have been a REAL bad batch!

Well, I'm no expert, but I'm not exactly a novice either, and I ultimately was never able to diagnose and repair the fault with mine.

In case you're interested, I used a Meanwell RT-65B to supply 5, 12, and -12V and a Meanwell RS-25-5 to supply the -5V.  That left me short because I still needed 15V and 3.5V according to the label on the PSU.  It turned out that for my application (the HP 53310A), the 15V was used only for the fan, so I simply used 12V and the fan works fine.  The 3.5V was obtained from the 5V through two diodes, and later I found that 3.5V is unused in my application anyway.  I took the top cover of the existing Boschert supply, did a small amount of sheet metal trimming, mounted everything on the cover and slid it back into the target machine.  The only "delicate" thing was that I had to cut off the cable connector (20 pins if I recall) and individually run the wires to a terminal block I also mounted next to the Meanwell supplies.  Whether my replacement supply was as noise free as the Boschert, who knows.  But at least if it breaks, I know exactly how to fix it.

vanhouten:
Usually I prefer fixing things over just replacing, mostly because of the challenge and learning experience... well sometimes because it is cheaper as well  :o
But in this case I tend to go for your second solution and order the replacements you suggested (might be cheaper indeed). Did you have any problems with calibration due to mismatching voltages (5V vs 5.2V etc)?
As I said my machine isn't too impressed by the voltages I offer it to feed from the AT-PSU. I hope that the attenuators and converters are still alive and just being picky about that.
So I will try to poke the Boschert some more and see how far I can get until the PSU's arrive.
Thanks for the input!
(If you have more, let me know  ;) )
Smith:
Mine had a ticking noise too. It was clearly noticeable while the scope was resetting itself.
vanhouten:
This seems to be a common issue with SMPSs. In the Tektronix-Troubleshooting-Guide mentioned earlier in this post this is described as an indicator to a conclusion that is not further explained  :palm: (page 34)
It just advises to check the resistance of the scopes power supplies in case of ticking noises.
I unhooked the PSU and placed a load resistor (10 Ohm) between the secondary 5.2V-output and common. This way two of the output voltages appear to be stable, which tells me that the defect is probably restricted to the secondary side and related to the individual circuitry of the respective rails (this would fit the bad-cap problem you experienced as well).
I will try to examine the working rails more closely then as a reference for the broken ones... if they still work  ;)
wn1fju:
You asked, "Did you have any problems with calibration due to mismatching voltages (5V vs 5.2V etc)? "

The Meanwell supplies I used all have adjustment pots.  The 5V supply has a range of 4.75 to 5.5V, so getting 5.2V was not an issue.

On my Boschert supply, I replaced ALL the electrolytics, the switching transformer, the opto-isolator, pulled and checked all the flyback diodes, checked all the FET/BJT regulators they put in the back end, and on and on.  I got close at one point, but never completely fixed it.  I keep it around in plain view to keep me humble.

As I said earlier, the replacement supply works well.  My only concern would be whether HP and Boschert engineered the original thing to have certain noise characteristics or switching transients that I am not getting with the Meanwell supplies and that might make the 545xx scope not perform as well.  Perhaps an expert can chime in on this thread???
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod