HP8596E Spectrum Analyzer repair

[james_s]

You don't ever find yourself in the Seattle area do you? If you did I'd be happy to pop that thing on my Sencore CRT analyzer and see what it says, or loan you an electrically compatible tube to test your monitor chassis with. I'm afraid I can't be a lot of help in terms of advice on jerry-rigging something as I've had a proper CRT tester/restorer for years and just use that.

If it turns out to be the tube you might contact Video Display Corp and see if they have anything compatible, or measure the tube and try to find something similar. If you can find something that physically fits, there's a very good chance that it will work. CRTs don't grow on trees, nobody is building or rebuilding them anymore and they are vanishing fast but they are still out there, I have bought brand new replacement CRTs for other things as recently as last year.

Worst case LCD monitor conversion is not too hard to do, although personally I'm a fan of CRTs and try to preserve them whenever possible.

Another option I forgot to mention earlier that you could try is simply let the thing run for several hours/days and see if it clears itself up. The flares look a bit dramatic but are unlikely to actually damage anything. Also look very carefully in the neck of the CRT and see if you can spot any arcing or mechanical problems, the neck is transparent so with some care you can visually follow most of the connections from the pins to the elements inside the tube. I've seen internal shorts caused by a flake of the graphite aquadag that came loose and lodged itself into the gun.

[KCT_99]

Hi James,

sorry, I rarely make it out west. It is a shame, that is such a nice analyzer and when the CRT works, it is very pleasing to look at. For Test Equipment like that I actually prefer the looks of a CRT over LCD, same goes for scopes. Thanks for your advise, I will have a closer look at the tube neck, maybe something can be seen there.

For now, I see if I can get a used CRT assembly of Ebay so I can put this analyzer back together.

[SilverSolder]

I'm with you on the CRTs.  There is just something cozy about the green glow...   there's a lot of magic smoke in there!

[vsmith]

Hi all, and to KCT_99, I am working on an 8595e with a dim display right now. I have taken the display assembly out of the analyzer (I do hope it will all go back together, theres a lot of pieces to the puzzle!) and I am just getting ready to try to rejuvenate the CRT with a newly acquired Sencore CR70 "Beam Builder" tester and rejuvenator. I will post the results here, but I also want to extend to you the possibility of you bringing your tube to my shop (home). Message me if you are near NYC and care to make a trip to use the Sencore.

My display, BTW, is visible only at the extreme end of adjustment range of the brightness and contrast trimpots on the display assembly. It's almost usable left at that extreme, if a little out of focus, but I want to try to get it working normally, so went to the trouble of hunting down and purchasing the Sencore.

More TK

[james_s]

Speaking from experience with the Sencore, if you see improvement, quit while you are ahead. Do not be tempted to hit it again to see if it gets even better, much more often than not that ruins the tube.

[vsmith]

I am cautiously optimistic. After figuring out the right pin out for the CRT and getting the Sencore "Universal Adapter" hooked up and the settings configured, my CRT showed very low emission. I opted for the "Automatic Restore" function which exercises the filament and cathode 3 times. The after reading for emission was way up in the green "good" region of the scale and the "life Test" which drops the filament voltage by a small amount, showed almost no drop in emission. Next step is putting everything back together, and hoping the analyzer still works! Thanks for that tip, James_S. Will keep that in mind.

[james_s]

Yep you're definitely ahead, sounds like an almost textbook perfect result. Definitely put it back together and see what you get. Dial the contrast down a bit and you will greatly extend the life of the tube.

[SilverSolder]

It is rather amusing to see a resurgence of the nearly lost art of CRT restoration in the year 2019!   

Well done. 

[vsmith]

@SilverSolder, yeah, I honestly never thought I would need a TV tube "Rejuvenator" (which I always thought was a scam, anyway) but I was wrong! It's a welcome addition to my shop (and the Sencore CR70 is nicely made and comes with well written documentation)

@James_s, yep, it is all back together (so many wires and screws!!!) and looks great. I did back off the contrast to about mid range, and adjusted the brightness so that with the f.p. intensity control full CW, the background is just dark. Normal viewing with decent focus is now at about mid range on the f.p. intensity control. I will say that the focus doesn't hold well once you start increasing the intensity control, but its fine with a normal viewing intensity. I call it a success, for sure.

This doesn't prove much, since there was no "before" photo, but here it is, with normal intensity! It's a good day here.

[james_s]

Looks great! The soft focus when increasing the brightness is a classic symptom of a worn cathode, the CRT restorers can't magically put a new coating on the cathode but as you've seen here they can squeeze more life out of an otherwise shot tube, sometimes significantly more. You'll probably find that if you test the cutoff it won't do so well as the middle of the cathode is likely more worn than the outer edges but for this application it doesn't really matter.

[Renate]

I'm losing track of of the status of the OP.

You want to figure out what's pulling down the -200V.
Did you actually put a scope on it to see the ripple?
Have you unplugged the focus pot to see if that's dragging it down?
The math on the voltages around the focus are wrong.
Is there breakdown/arcing in the focus pot to a grounded shell?

[analogRF]

Well, yeah I would not mind an LCD upgrade if there is such LCD module available.       Can you point me to it ?


In the meantime I installed the overhauled CRT assembly back into the analyzer, not much luck, the display is very dim but sometimes and intermittently comes to full brightness or even brighter than I'd think is normal. When it does so, is also out of focus. But mostly it is dim.

I have been working on this CRT assembly for a couple hours now and  measured a few voltages:

+60V rail measures +75V
-200V rail measures only -142V

I think this could be the problem. I replaced diode D3 and R76 but did not bring the negative voltage to -200V,  so I guess the Flyback transformer is toast. 

https://www.ebay.com/itm/NewScope-0Jr-LCD-kit-for-HP-8591E-8593E-8594E-8595E-8596E-Spectrum-Analyzer/133205624430?hash=item1f03ac866e:g:mUUAAOSwEgRdo8T7

[james_s]

The LCD kit has already been discussed, we're trying to preserve the original CRT display.

Not to mention $349 strikes me as obscenely expensive for a small LCD monitor. I'm sure a NOS CRT could be found for less than that.

[Miti]

The LCD kit has already been discussed, we're trying to preserve the original CRT display.

Not to mention $349 strikes me as obscenely expensive for a small LCD monitor. I'm sure a NOS CRT could be found for less than that.

I agree, the CRT looks better than the LCD but we should have a backup plan, a little cheaper than $350.
Talking about preserving the CRT, I opened my HP8591E that supposedly has an intermittent display. Knowing myself, I would probably replace the caps, maybe I can improve the sharpness (maybe not) a bit, and get rid of the horizontal line flash when I turn it off. I suppose the vertical supply cap is dry. Does anyone have a schematic of this display model? The drivers are AN5763  and AN5790.

[Miti]

Hi KCT_99,

Did you repair your SA's CRT?
If you are interested in replacing it with an LCD for cheap, you may find this helpful:

https://www.eevblog.com/forum/testgear/hp-8594e-replacing-the-green-crt-with-lcd/new/#new