Author Topic: HP8596E Spectrum Analyzer repair  (Read 2790 times)

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Offline KCT_99

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HP8596E Spectrum Analyzer repair
« on: September 30, 2019, 05:12:12 pm »
Hi,

well, I got my dirty little fingers on a nice mint HP8596E Spectrum Analyzer, unfortunately it has a problem, the CRT remains blank as if there is a problem with the HV power supply. When I plug a monitor into the video output, I get good display on the video monitor so the analyzer itself works fine.
So I am looking for a service manual or at least a schematic for this unit, but can't find it.
Can someone help me ?
 

Offline pbarton

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Re: HP8596E Spectrum Analyzer repair
« Reply #1 on: September 30, 2019, 07:08:02 pm »
You need the HP 8596E Component-Level Information Packet (CLIP), go to…
https://www.keysight.com/gb/en/home.html
Then search on the Keysite website using this term:   5963-2951 CLIP
Service Guide:-
http://www.keysight.com/upload/cmc_upload/All/08590-90316.pdf

To repair the OmniVision monitor you will require the Service Guide…
http://oz1db.dk/hp/omnivision_man_lp06xx_rev0_0611.pdf
Try replacing C14, a 4.7uF capacitor coupling the base drive to the horizontal output transistor.  Its the only radial lead cap, laying parallel to the PCB.
http://oz1db.dk/start_eng.html   Then click on "HP859X repair"
Otherwise you may need to change the remaining 10 small electrolytic caps in the OmniVision CRT display, about the size of your little finger nail.
If you replace those, it should start working again.
« Last Edit: September 30, 2019, 09:53:01 pm by pbarton »
 
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Offline KCT_99

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Re: HP8596E Spectrum Analyzer repair
« Reply #2 on: September 30, 2019, 08:04:01 pm »
Many BIG THANKS for your kind help !  :-+
 

Online Miti

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Re: HP8596E Spectrum Analyzer repair
« Reply #3 on: October 01, 2019, 02:44:13 am »
My Hp8594e had a similar issue. The culprit was a dry electrolytic capacitors in the display module. Take the display module out and measure the esr of the caps. You'll catch the dead one pretty easy.
That big spark at power up was by design!
 

Offline KCT_99

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Re: HP8596E Spectrum Analyzer repair
« Reply #4 on: October 01, 2019, 07:43:53 pm »
Well, I have the CRT assembly out and replaced all electrolytic's. Most of them seem dried up measuring less rated capacitance and quite high ESR for my taste. It appears someone was in there before me, it seems the capacitors were replaced once already. I noticed the CRT itself has a bad scratch pretty much in the center of it.  :palm:
I was super careful dismantling the analyzer, I don't think I did that to it. I wonder what it took to scratch the glass like that. I hope the CRT is still good. Anyway, I am now putting it all back together now, fingers crossed.
 

Offline TheSteve

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Re: HP8596E Spectrum Analyzer repair
« Reply #5 on: October 01, 2019, 07:54:57 pm »
Maybe time for an LCD upgrade :)
VE7FM
 

Offline KCT_99

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Re: HP8596E Spectrum Analyzer repair
« Reply #6 on: October 02, 2019, 12:03:30 am »
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.  :(



 

Offline KCT_99

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Re: HP8596E Spectrum Analyzer repair
« Reply #7 on: October 02, 2019, 03:57:58 pm »
Well, poking around a bit more, this is what I got. The socket seems surprisingly clean. The filament measures about 49 Ohm. and the signal waveform on the 200V winding (pin 8 FLBT DCA) looks like this, getting about 210Vpp. I am not experienced with CRT and tube stuff, so I have no clue if this is a decent waveform but I do not like the hiccup on the rising edge. I also pulled R75 to see if the -200V rail normalizes, but nope still short at -140V. R75 and C49 measure good.

What do you guys think ?

 

Online Miti

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Re: HP8596E Spectrum Analyzer repair
« Reply #8 on: October 02, 2019, 05:28:40 pm »
Regarding the LCD, I tried to find one for my HP 8594E and there's nothing available. Probably you won't find one for HP 8596E either. I tried to adapt something from ebay with very little success. The video signals are not standard.
That big spark at power up was by design!
 

Online SilverSolder

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Re: HP8596E Spectrum Analyzer repair
« Reply #9 on: October 02, 2019, 05:42:37 pm »
... I guess the Flyback transformer is toast.  :(

I wouldn't condemn it just yet -  typically, if the transformer is bad, there will be picture geometry problems as well (e.g. picture not filling full width of screen etc.)

Look around for power resistors that have changed value, or have solder connections that have gone bad from the heat...   that kind of thing.  The "blinking" effect sounds like it might be a connection issue somewhere.
 

Offline KCT_99

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Re: HP8596E Spectrum Analyzer repair
« Reply #10 on: October 02, 2019, 08:01:31 pm »
Thanks for the help guys,
well the soldering looks generally quite good, I would not think it to be a soldering issue. What I have trouble with, why would the -200V rail be this far off when the other rails seem to be ok.  I can confirm, there is no issue with image geometry, only brightness or contrast issue.  Yeah, I had a quick look at epay but nothing jumped at me for replacement.

Any comment on the waveform ?

I guess I am verifying every passive on this assembly now. |O
 

Offline KCT_99

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Re: HP8596E Spectrum Analyzer repair
« Reply #11 on: October 04, 2019, 12:10:00 am »
Well, I am not having much luck with this CRT module. I replaced R53, R50, R51, R86 on the brightness circuit except R52 the master pot itself. I increased C36 to 220nF. This seems to tame down the brightness flareups a bit. The voltage on the R52 wiper is constant when I get these flare ups. I get these brightness flareups also with the front panel pot disconnected. The 600V rail is constant at 567V. I also replaced R27, R55, R59, R76.  I found that during a flareup the voltage drop over the 1k R59 increases from about 50mV to about 350mV. I had a meter directly on the CRT pin 1 and there the voltage changes from about -50V to +30V during a flareup. Overall the image is not really sharp as I would expect it, the focus dial R28 is dialed all the way to the positive side.
Unfortunately I can not verify the HV coming from the FLB. I am running out of ideas, could the CRT itself be bad ?
 

Online SilverSolder

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Re: HP8596E Spectrum Analyzer repair
« Reply #12 on: October 04, 2019, 01:53:58 pm »
Before condemning the CRT, it's probably worth checking that the high voltage rectifier etc. are in good shape.  The HV rectifier may be a voltage doubler or tripler, filled with diodes and capacitors that all lead a hard life.  If the focus voltage is wrong, and the EHT is too low, you would likely see reduced brightness and focus issues.

Not sure of the best way of measuring this without a proper HV probe,  but perhaps connecting 10 - 20  resistors in series inside a heatshrink sleeve could make a crude probe, where you measure the voltage across the resistor closest to ground...
« Last Edit: October 04, 2019, 01:56:46 pm by SilverSolder »
 

Offline KCT_99

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Re: HP8596E Spectrum Analyzer repair
« Reply #13 on: October 05, 2019, 02:27:49 am »
Hmm, well alto I do not feel comfy messing around with this high voltage, as it could be a killer, I guess I have to try at least.
My Meter is rated up to 1000V I believe so how high of a voltage is expected there ? 15kV ?
Also, I don't think the HV rectifier can be serviced, I think it's part of the transformer and fully encapsulated.
 

Online SilverSolder

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Re: HP8596E Spectrum Analyzer repair
« Reply #14 on: October 05, 2019, 12:23:45 pm »

That sounds like a reasonable guess.

All we would be looking to do is confirm that the high voltage is not stable (i.e. is it jumping around and causing the bright/dark behavior).  The reason for using multiple resistors is to avoid flash-over...  e.g. with 15 equal resistors, each one needs to handle 1,000V.   Depending on what you have in the parts drawer...  :-)

One hand in the pocket at all times...
 

Offline KCT_99

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Re: HP8596E Spectrum Analyzer repair
« Reply #15 on: October 05, 2019, 10:29:55 pm »
I don't have such high resistance resistors, I would have to buy some. The local surplus store has some larger size like 1/2 W 1.8M. A couple of them would do it, I guess. Alto if I would just go ahead and buy a new transformer, this might be the easy and perhaps much more safer route as I am very uncomfy working with such high voltages.
 

Online SilverSolder

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Re: HP8596E Spectrum Analyzer repair
« Reply #16 on: October 06, 2019, 12:27:27 am »

It might be an expensive part if the diagnosis is wrong...   even if the odds are good...
 

Offline james_s

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Re: HP8596E Spectrum Analyzer repair
« Reply #17 on: October 06, 2019, 05:26:01 am »
I don't have such high resistance resistors, I would have to buy some. The local surplus store has some larger size like 1/2 W 1.8M. A couple of them would do it, I guess. Alto if I would just go ahead and buy a new transformer, this might be the easy and perhaps much more safer route as I am very uncomfy working with such high voltages.

The high voltage in a small monitor like this is not particularly dangerous, getting zapped does not feel good but it is much less likely to actually hurt or kill you than 120V from the wall. While it's not impossible, I would be very surprised if the flyback is bad. Every time I've had a bad flyback it has been either completely dead or arcing.
 

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Re: HP8596E Spectrum Analyzer repair
« Reply #18 on: October 06, 2019, 11:35:03 am »

Is there a circuit diagram for this thing?
 

Offline KCT_99

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Re: HP8596E Spectrum Analyzer repair
« Reply #19 on: October 06, 2019, 01:28:53 pm »
CRT Circuit diagram: see links in second post.

http://oz1db.dk/hp/omnivision_man_lp06xx_rev0_0611.pdf

To measure the HV, I would have to put some copper tape at the contact point on the tube to have something to connect to.
My worry is that it could arc to nearby wires as everything is so tightly crammed in there and kill one of the chips.  I am very hesitant to mess with the HV on this thing.

What I don't understand are the brightness flareups, I would expect it to be the other way around as having normal brightness and then diminished brightness intermittently.

Could it be that one of the HV rectifiers inside the flyback is mostly half dead and occasionally comes back to life giving full HV ?
 

Offline james_s

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Re: HP8596E Spectrum Analyzer repair
« Reply #20 on: October 06, 2019, 03:46:05 pm »
If the HV is changing then the size of the picture will be changing too. The higher the HV, the smaller the image will get, it is normally pretty obvious when there is a problem here. I would be looking closely at the G1 and G2 pins as those will have the greatest effect on brightness.
 

Offline KCT_99

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Re: HP8596E Spectrum Analyzer repair
« Reply #21 on: October 06, 2019, 06:27:31 pm »
Thanks for your help. So far it does not appear the image size is changing during these flareups, perhaps at most in a minor way.
The CRT socket seems fine, no trace that something is arcing or burning, all connections ring through the other end just fine. Perhaps the socket itself doe not make good connection on a tube pin. It does not appear the socket can be opened without destroying it.

 

Online SilverSolder

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Re: HP8596E Spectrum Analyzer repair
« Reply #22 on: October 06, 2019, 10:14:24 pm »
I attached the diagram page from the PDF, for ease of reference, with some notes from the conversation so far...

The focus pot being at one extreme is interesting.  What is the voltage on its wiper, and what happens to that voltage as you rotate the focus pot?

Does the -200V rail recover if you unplug the focus pot?

These idea is to explore the possibility of internal shorts in the CRT, looking for weird voltages.





 

Offline KCT_99

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Re: HP8596E Spectrum Analyzer repair
« Reply #23 on: October 06, 2019, 11:17:04 pm »
Thanks for your help. I added some info to the schematic and called it Rev.2 Everything highlighted with a blue icon I replaced with a new component. On the wiper of the focus pot R28 I have about +135V. I have yet to measure and observe the wiper voltage as I turn the pot as well as what happens to the -200V rail when disconnecting the pot and will report back on that.

For fun and giggles, I lifted one pin of C15, makes no difference to the flareup issue.

EDIT:
Well, when measuring the -200V rail, I get a constant reading of about -140V regardless where I set the focus wiper. When I unplug the focus pot, the -200V rail mildly recovers to about -142V.  The focus wiper voltage nicely continuously changes between +135V and -140V.

R27 replaced with a new resistor 1.8 M.

Below is a picture of the screen as I see it, not exactly as sharp and crisp as I remember having seen screens like that.
« Last Edit: October 07, 2019, 12:55:25 am by KCT_99 »
 

Offline james_s

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Re: HP8596E Spectrum Analyzer repair
« Reply #24 on: October 07, 2019, 01:54:27 am »
It looks like you've got some pretty substantial bleeding to the right which suggests clipping in the video amplifier. A short in the tube is a distinct possibility but I wouldn't be too quick to condemn it. The low voltages point to an obvious problem somewhere, do they recover if the CRT is unplugged?
 

Online SilverSolder

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Re: HP8596E Spectrum Analyzer repair
« Reply #25 on: October 07, 2019, 11:43:00 am »

Hard to say what is an artifact of the photography (it is not easy to capture a CRT image accurately) and what is actual blur.

However, it is clear that the CRT is very "tired" looking with ghost text burned into the phosphor (black lettering) from many hours of use.  (Is the text actually from this spectrum analyser?  It looks like the ghost text was burned in a different position on the screen than the current text being displayed.)

As a CRT gets up in the hours used, the emissivity of the cathode falls, and the tube becomes dimmer.  This can be compensated to some extent by cranking up the brightness, (and cranking up the filament voltage), but it will only go so far and isn't really a permanent fix.
 

Offline KCT_99

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Re: HP8596E Spectrum Analyzer repair
« Reply #26 on: October 07, 2019, 04:54:19 pm »
Well, I did more measurements.

Rails      with CRT connected         with CRT disconnected
+600V              +568V                               +570V
-200V               -138V                                -139V
+60V                +70V                                 +70V

Then just for good measure I replaced R80 also, now 200 Ohm.

And I managed to take video of the event. Please note, during these flareups focus sharpens right up for brief period of time as seen in the lower left on the screen in the video. Also, for some reason, when I do connect the remote brightness pot, these flareups seem to occur more often and more pronounced, it seems. This video was taken with the remote pot connected.

Video download link: (Will be deleted on 14 October, 2019)
https://wetransfer.com/downloads/6dd972e01237a7c9e5999fe48b1be59020191007164902/e16a280e1942552d349837e0de905c7f20191007164902/1661fe
« Last Edit: October 07, 2019, 04:59:05 pm by KCT_99 »
 

Offline KCT_99

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Re: HP8596E Spectrum Analyzer repair
« Reply #27 on: October 07, 2019, 04:58:16 pm »
Here another attempt to take a reasonable picture of the screen image. I used a magnifier and cell phone camera.
Yes, this analyzer was used substantially, but over all it does seem to be in a very good shape. The burned in image seems 'normal' as I have seen this on other spectrum analyzer CRTs of this HP type.

 

Offline james_s

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Re: HP8596E Spectrum Analyzer repair
« Reply #28 on: October 07, 2019, 09:03:34 pm »
Do you know anybody with a CRT tester? If you have any arcade collecting groups in your area that might be a good place to start, they're also pretty cheap on ebay as they are a niche thing these days however they tend to be rather bulky so shipping can be expensive.

Can you try monitoring the voltage on the G1 and G2 pins during one of the flares? It's quite possible that you have an internal arc in the electron gun or the flyback causing that. You might try gently tapping on the CRT neck with something like a plastic screwdriver handle and see if you can get it to act up.

The low -200V rail certainly suggests a fault in the circuit somewhere, the other rails are close enough to look pretty reasonable to me but -200V is way low.
 

Offline KCT_99

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Re: HP8596E Spectrum Analyzer repair
« Reply #29 on: October 07, 2019, 10:28:27 pm »
So I opened up the CRT socket, found nothing indicating trouble. I removed each contact re-soldered it and gently pushed the contact forks to have more bite on the CRT pins when engaging. This seems to have helped noticeably with image sharpness. However the flareups still persist. I had the scope probe 10:1 connected to Pin 2 CRT to view the video signal during a flareup. This signal remains absolutely stable. as seen in the image below. Then I had the scope probe 10:1 connected to Pin 1 CRT, there I can observe an substantial instability during these flareup events, as seen in the video linked below. Average DC is rising erratically.

Videos Will be deleted on 14 October, 2019

https://wetransfer.com/downloads/3d511248784e4a874eb1fcb7fd5974a620191007214850/d4d6f38e229dc06bb70a7342661add3320191007214850/80b18e

Yeah, i tried already gentle tapping the boards, connectors, transformer etc. did not seem to provoke this problem. I tried cold spray as well. It does not seem to impact this instability in any way.

Initially, the -200V rail been only -140V seemed the obvious problem, but at this point it is still inconclusive to me. Alto been quite low this voltage remains stable during these flareup episodes.

 

Online SilverSolder

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Re: HP8596E Spectrum Analyzer repair
« Reply #30 on: October 08, 2019, 12:07:47 am »

The pictures are good.  The video is excellent, that really got the issue across well.  Thankfully, CRTs are their own oscilloscopes!

First, notice how the "glowing shadows" of the text point towards the center of the screen from top left and top right:



These glowing shadows are caused by the electron beam no longer being perfectly round, and it is rotating as it moves across the screen (the shadow points the opposite direction on opposite sides of the screen).  This means we can completely rule out the video amplifier and concentrate on why the CRT is defocused, weak, and performing flare-up tricks for us.


Let's review how this CRT probably works in basic terms to help the investigation:



1.  The filament (3,4) heats the cathode (2) which causes a cloud of electrons to boil off its surface. 

2.  The control grid (1) is shaped like a cup with a pinhole in the bottom facing the screen - the control grid is more negative than the cathode which has the effect of repelling the electrons into a little ball around the center of the cup near the surface of the cathode.  The control grid voltage controls the overall brightness of the screen (beam current).

3. The accelerator grid (6) is a hoop shape that attracts the electrons out through the pinhole with a high positive voltage.  By the time the electrons reach the hoop, they are going so fast that they continue straight on.  Very few electrons actually hit the grid so we don't expect to see much current coming out of pin 6.

4. The electrostatic focus lens consists of three short cylinders:  the pre-accelerator (connected to EHT), the focus control (7), and another accelerator also connected to EHT.  The beam will be precisely focused and moving at very high speed when it comes out the other side.

5. The beam hits the screen, which is conductive and lets the electrons be sucked out of the tube by the EHT connection, which return the electrons to ground to start the cycle all over again. 

6. The tube is coated inside and outside with a conductive graphite material called Aquadag.  The inner coating is at EHT voltage, the outer is at ground.  The glass between the coats acts as the plate of a giant capacitor.  This capacitor smooths the EHT and retains charge for days/weeks after the CRT has been switched off and can give the unwary technician quite a surprise.  This capacitance has to be discharged in order to work on the EHT section safely.


With reference to the explanation above, what could be wrong with the unit?  Well, we can see from the pictures and the video that we have both a focus and a brightness problem simultaneously.  Since the electrostatic focus lens on this particular tube is primarily driven by the EHT,  and since the brightness of the tube is also dependent on EHT, the common denominator is - the EHT supply.  It seems prudent to find a way to measure (or even trace on an oscilloscope) the level of the EHT in order to be able to either confirm or eliminate EHT instability as the root cause.
 
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Offline tautech

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Re: HP8596E Spectrum Analyzer repair
« Reply #31 on: October 08, 2019, 12:32:20 am »
@SilverSolder
I don't mean to nitpick only offer further clarity to your great post.

Typically in older instruments there are several voltage rails and we refer to those to 60V or so as LV while those say of the CRT plate drivers of ~120+V are the HV.
When we mention EHT it's normally referring to the cathode voltage applied to the CRT and is always negative and often ~-2kV and more.
The beam acceleration voltage is usually derived from the EHT via some uneven stage # multiplier (3 or 5 is most common) but is positive and referred to as PDA (Post Deflection Acceleration) voltage.

This large voltage potential difference, commonly 6, 8, 10 or more kV accelerates the electron beam at speeds required for the particular CRT display refresh rate/BW of the instrument and/or the phosphors used.
Avid Rabid Hobbyist
 

Offline james_s

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Re: HP8596E Spectrum Analyzer repair
« Reply #32 on: October 08, 2019, 12:42:00 am »
It sounds like we are getting terms commonly used for electrostatic deflection CRTs mixed up with those used with magnetic deflection CRTs as this one is. A magnetic deflection CRT has no plates and the cathode operates near ground potential, the EHT is a positive voltage feeding the final anode, in the case of a tube of this sort it will generally be around 6-9kV which almost universally comes directly from a single HV winding on the flyback transformer, half wave rectified by a HV diode which is often internal to the flyback and then filtered by the capacitor formed by the CRT itself. I have not seen the schematic for this particular monitor but the focus and G2 voltages are typically derived from a winding separate from the main EHT winding on the flyback, it's possible that the flyback is arcing internally or it could be a fault in one of the rectifier diodes or other components involved in conditioning these voltages. While the EHT could be fluctuating as I said earlier that *usually* results in an obvious "breathing" effect where the picture changes size at the same time as the brightness is also fluctuating.

Apologies if this has already been mentioned but do any of the flyback-derived voltage rails fluctuate when the picture is doing its thing? I still think the fault could go in one of two directions, one is a circuit fault causing the focus and G2 voltages to fluctuate which causes the effects noted in the picture. The other possibility is an internal fault in the electron gun in the CRT that is dragging these voltages around. A third possibility slightly different than the first is electrical leakage somewhere, I forgot to ask if there is any glue or other contamination on the board? I used to see fairly often a white glue used to reinforce parts on PCBs would turn brown and become slightly conductive. The focus and G2 voltages are very high impedance sources intended to deliver essentially zero current so it doesn't take much leakage to bog them down.
« Last Edit: October 08, 2019, 12:43:35 am by james_s »
 

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Re: HP8596E Spectrum Analyzer repair
« Reply #33 on: October 08, 2019, 12:45:03 am »

I have probably spent far too much time poking around inside old television sets, my side line as a college student! -  so I am probably using TV terminology.

 

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Re: HP8596E Spectrum Analyzer repair
« Reply #34 on: October 08, 2019, 12:47:40 am »
[...] I have not seen the schematic for this particular monitor but the focus and G2 voltages are typically derived from a winding separate from the main EHT winding on the flyback, [...]

The illustration in my previous post is from the diagram (which is posted earlier in this thread).   This CRT appears to have a somewhat unusual focus and accelerator grid arrangement driven straight from the EHT.
 

Offline james_s

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Re: HP8596E Spectrum Analyzer repair
« Reply #35 on: October 08, 2019, 12:52:11 am »

I have probably spent far too much time poking around inside old television sets, my side line as a college student! -  so I am probably using TV terminology.

Your terminology is correct as far as I noticed, this is a magnetic deflection raster monitor so it is essentially a TV minus the tuner and audio stuff. IIRC these even use bog standard NTSC format composite video.
 

Offline james_s

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Re: HP8596E Spectrum Analyzer repair
« Reply #36 on: October 08, 2019, 01:04:03 am »
Ok now I found the manual linked earlier with the schematic, having that is very useful.

The G2 and focus are both fed by a 600V rail derived from the primary side of the flyback, this is essentially a boost converter and the HV secondary can be ignored for a moment. This looks very standard to me, it's pretty much the same circuit used by most small raster monitors and portable TV sets that are powered by low voltage DC. So I suspect that 600V rail is fluctuating, this could be the flyback itself, or it could be either of those diodes or the capacitor C23, or it could be something external loading it down. Or it could be an issue with the 200V line, if something is loading that down it will cause other voltages to be wrong. A HV probe would be handy here just as a sanity check on the EHT. Lacking a real one I would probably just make one with a bunch of 1M resistors in a plastic tube, the circuit is simple enough. One need not do any live probing, just slip the end under the anode cup and ground the other end of the divider, hook it up to a multimeter and then power up the monitor while not touching any of that stuff while it's live.
 

Offline KCT_99

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Re: HP8596E Spectrum Analyzer repair
« Reply #37 on: October 08, 2019, 02:47:43 am »
Thanks for your help.

Unfortunately, I don't know anybody with a CRT tester. We used to have a TV repair shop in town, but they are long gone.

I had measured the rail voltages during the flareups, the +600V, +60V and -200V rails are stable.

The only rail not yet verified is the HV. For that, as suggested, I will have to make up this large voltage divider.
I see if I can manage to do that tomorrow, got to go resister shopping first. Then I will attempt to make a safe measurement.

I could also disconnect the -200V rail from the rest and see if it recovers.

Also, I will thoroughly clean the board of flux residue. They used white silicone to glue some electrolytic to nearby coil. I guess this is to give the coil mechanically stability. The silicone is only applied on the component side. I see if I can remove the silicone for now.
It appears the silicone was used around L1, C17,C38 and possibly R25.  Also applied to L2, C19 and heat-sink for Q2.
« Last Edit: October 08, 2019, 02:53:48 am by KCT_99 »
 

Offline james_s

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Re: HP8596E Spectrum Analyzer repair
« Reply #38 on: October 08, 2019, 04:23:45 am »
It's sounding to me like it may be a fault in the CRT, if the 600V line is stable and the brightness and focus are surging that doesn't leave much else. Do check the HV though and let's see what that's doing.

If you can find one of those cheap 5" portable B&W TVs you could temporarily swap the tube from that into the monitor. The pinout on small tubes like that is pretty standardized and they are electrically similar enough to work. B&W monitors have no convergence or purity to muck with so swapping the yoke onto the TV tube is not difficult. Conversely you could test the tube you have with the electronics of the TV.
 

Online SilverSolder

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Re: HP8596E Spectrum Analyzer repair
« Reply #39 on: October 08, 2019, 12:17:15 pm »
Don't forget to discharge the CRT capacitance...  and remember that it can recover quite a bit of charge after the first discharge, as the Aquadag has high resistance and acts like a big RC filter.

How to discharge:


« Last Edit: October 08, 2019, 02:37:19 pm by SilverSolder »
 

Offline KCT_99

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Re: HP8596E Spectrum Analyzer repair
« Reply #40 on: October 08, 2019, 01:22:43 pm »
Thanks guys, I will be careful and keeping my left hand in the pocket. :)
 

Offline KCT_99

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Re: HP8596E Spectrum Analyzer repair
« Reply #41 on: October 08, 2019, 05:46:37 pm »
Alright, just got back from resistor shopping, but I have had a second though on this while creeping along in my car. So before I go though this HV exercise I do something else.

We know, G1 looks very suspicious as I have measured there the instability while elsewhere there is little to none instability that stands out in any way. And here we are on to something I believe. For fun and gigles, I put 220nF 250V capacitors to ground on both sides of R50. This seems to tame these flareups right down and gives almost a constant brightness but without much control over it. With the Sharpness I could kind of live with altho I would want the image to be sharp.

Please bear with me here for a second as I explain my theory. I checked on ebay, and found two such CRT monitors offered, both seem to have noticeable screen burn-in's as bad as mine. Sure this could just mean operators cranked up the brightness with little regard to CRT life, but I suspect a design flaw here. I believe many of these CRT of this type suffer from the same issue. Someone suggested to look for contamination that could offer a creep path for high voltage I looked the CRT socket as suggested and as many have found problems there, at least on some TV. So at the CRT socket life is good, but what about on the other end of the connection ?

The thing that kept me up at last night is that this thing flares up in brightness not down, this means G1 gets more positive. Confirmed as seen in the video I took of G1. Everything is stable at some DC on G1 and then suddenly I see the G1 rise erratically just to settle back down to about the same DC for a while and then this spectacle repeats.

I suspect intermittent creep currents but not inside the CRT tube, but outside of it.

Looking at the PCB diagram, G1 (GRN) is located right next to G2 (RED) on this PCB, perhaps separated by about 4mm or even less than that. Other CRT connection are clustered in very close proximity there as well, except Yellow, the video signal on the Cathode. This signal is far away on the opposite side of the board and well clear of anything nearby.
So G2 (RED) sitting neatly at a healthy 567V just 4 mm away from G1 (GRN).... :palm:
Hmmmm....

I am not sure what the Layout guy was thinking when squishing these signals this tightly together and on top of that running a jumper J1 (G1) half across the board when he could have conveniently have G1 (GRN) located at the other end of J1. Saving himself the trouble of putting the jumper, using up board space while easing up the CRT connection congestion. :palm:
Hmmmm....
Must have been a bad Monday, I guess....

My theory is that, I might have creep right there between GRN and RED, either on the component side or on the bottom. I suspect on the component side, its very crowded an the wires leading to the CRT socket have a little contact crimped to them which is then soldered into the board.

To confirm this theory I will dismantle this entire assembly to get good access to clean this board thoroughly, I will then apply something to add insulation to these connections, I am thinking using my wife's finger nail lacquer or perhaps some silicone. Then after reassembly I have a strong feeling the flareups will be gone.

The more I look at this exceptionally terrible layout design, the more I lean towards my theory.

What do you guys think ?

Does this sound reasonable for a theory ?
 

Online SilverSolder

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Re: HP8596E Spectrum Analyzer repair
« Reply #42 on: October 08, 2019, 06:40:08 pm »
The theory sounds relatively easy to check.  Maybe lift the jumper and solder the wire to the end of it?

In an earlier post, you said:  " I found that during a flareup the voltage drop over the 1k R59 increases from about 50mV to about 350mV. I had a meter directly on the CRT pin 1 and there the voltage changes from about -50V to +30V during a flareup."

If R59 is being driven from the side away from the CRT (rather than the CRT driving it), your theory begins to look very good!
« Last Edit: October 08, 2019, 07:31:07 pm by SilverSolder »
 

Offline tautech

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Re: HP8596E Spectrum Analyzer repair
« Reply #43 on: October 08, 2019, 07:01:03 pm »
I've had CRO's with unstable CRT performance and generally replacing all high value (1M+) resistors and HV caps fixes it. The resistors drift high with age and caps leak and do crazy things with HV on them.
Very occasionally a HV zener or HV diode can be a problem too.

Don't lose sight that much of the higher voltage components are under some stresses and BTW 4mm clearance for 600V is plenty.
Avid Rabid Hobbyist
 

Offline james_s

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Re: HP8596E Spectrum Analyzer repair
« Reply #44 on: October 08, 2019, 07:17:09 pm »
CROs have electrostatic deflection tubes using vector deflection, this is a magnetic deflection tube with raster deflection. The circuit designs typically used differ enough that I rarely see the same sort of problems with one as I do with the other. Most raster monitor problems I've encountered are failed electrolytic capacitors, bad solder joints, occasionally shorted semiconductors, and internal faults in the CRT. Flybacks occasionally fail but most of the time when that happens it pops the horizontal output transistor and the monitor goes dead, or it visibly arcs or has no HV output at all. It's been very rare that I've found any faulty resistors in a raster monitor but obviously it's worthwhile to check.

Screen burn is normal in this sort of instrument, they have a lot of static text and graphics on the display whenever they are powered up, and they have typically spent many hours powered up, it's the nature of the beast. Really, really heavily burned tubes are usually pretty tired but for the more moderate ones it's a crap shoot.
 

Offline KCT_99

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Re: HP8596E Spectrum Analyzer repair
« Reply #45 on: October 09, 2019, 03:36:30 am »
Well, in short, my theory did not work out. The flareups still persists.  |O

I took this thing apart again and throughly cleaned the PCBs, noticing they were not properly cleaned when manufactured, virtually every solder joint had some flux residue even on the component side.

I rewired G1 and G2 such that they are separated well from each other, I also put nail lacquer on the higher voltage part leads and solder joints.

So now I am back to square one. I guess now I have no further excuse to avoid messing with the HV. Altho I don't think this is a HV problem.

I was wondering why would they do a 270k R50 with a 1k R59 in series, while the 1k is a fat one. It does not make sense to me at all at this point. For the time been, I put a 2k and another 2k in series, so I have now 270k + 2k + 2k. In between the 2k's I put a 220nF to ground. This tames the flareups a little bit and slows things down altho it does nothing about the absolute brightness variation. Brightness is all over the place, from very dim to somewhat normal and then super ultra bright so much so I worry I could burn something out. For brief periods the image is quite pleasant and acceptable.

I tried to locate a CRT but no luck. It could be the company is long gone.

BWL 779009 MTI Monitronics

Coming to the realization there is not much more I could do, sucks.

Next thing to do, might be taking some money and sniping a CRT assembly of ebay.  :(

.
 

Offline james_s

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Re: HP8596E Spectrum Analyzer repair
« Reply #46 on: October 09, 2019, 04:51:47 am »
I suspect you've got an intermittent fault in the CRT itself, but I wouldn't be too quick to condemn it. Can't you find one of those cheap 5" portable B&W TVs? I've picked up quite a few of them at garage sales and thrift stores for a few dollars. I use them as monitors for various things and convert them to vector monitors but they would be handy for testing tubes like yours too.

Might not even be too hard to find a tube that is compatible with your monitor and the correct size. CRTs are very easy to sub in many cases, there are two common neck sizes, beyond that most of the differences are in the physical mounting details. There are three common phosphors used in small monochrome tubes but for your application it doesn't really matter, a white or amber phosphor would probably look just as good.

If it does turn out to be a tube fault, there is a reasonable chance you can blow out the short, my CRT tester uses a charged capacitor across various pins to do this.
« Last Edit: October 09, 2019, 04:53:41 am by james_s »
 

Online SilverSolder

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Re: HP8596E Spectrum Analyzer repair
« Reply #47 on: October 09, 2019, 12:09:35 pm »
Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth.
-- Arthur Conan Doyle

Going back to first principles, no significant current should flow into (or out of) any of the grids of a CRT, it is a voltage controlled device.

The fact that you measure such a high current for the control grid during the flare-up is a red flag and could point to some kind of leakage issue inside the CRT.

Still, it would be irritating if it turned out to be a bad HV rectifier?  The last non-eliminated possibility...

In your last picture, the "glowing shadows" are pointing the opposite way from the earlier one -  indicating a vastly different focus voltage or other major change of the tube operating point...
« Last Edit: October 09, 2019, 12:13:29 pm by SilverSolder »
 

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Re: HP8596E Spectrum Analyzer repair
« Reply #48 on: October 09, 2019, 01:08:58 pm »

This article on all the ways a flyback transformer can fail (including causing blinking power) may be of interest:

http://www.electronicrepairguide.com/testing-flyback-transformer.html
 

Offline KCT_99

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Re: HP8596E Spectrum Analyzer repair
« Reply #49 on: October 09, 2019, 02:27:02 pm »
Thanks for your help.

Well, at this point, I am not sure what to do further. Yes, I could test the HV on the Transformer, but I realize if I do need a new transformer or a new CRT they are equally hard to impossible to get. So what are my options at this point ?

If there is something funny going on in this tube, I suspect then between G1 and G2.  As last ditch attempt, could I use the 600V rail to attempt brutally blowing out a short ? I think I have some HV capacitors laying around somewhere.

If I understand correctly, I would unplug the CRT socket and temporarily connect G1 to ground and then hit G2 with 600V and a couple micro farads in hopes the short blow open and not welding short short ?
What about the resulting metal vapor inside the tube that might be generated in this attempt, would that not make things for creep much worse ?

I think, perhaps, before attempting that, I should measure on G1 and G2 again. If I measure G1 to G2, I would expect some voltage around 500V and during a flareup this voltage should drop. Also, measuring simultaneously on G1 again this voltage should rise.
Perhaps adding a third meter on G2 which should also slightly drop during the flare up event.

Would this be enough proof for a faulty CRT and for the blow out attempt ?

If all fails I might have to eat it and buy a well used spare display with potentially the same issue, this sucks.
 

Offline james_s

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Re: HP8596E Spectrum Analyzer repair
« Reply #50 on: October 09, 2019, 10:19:59 pm »
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.
 

Offline KCT_99

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Re: HP8596E Spectrum Analyzer repair
« Reply #51 on: October 10, 2019, 01:14:01 am »
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.
 

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Re: HP8596E Spectrum Analyzer repair
« Reply #52 on: October 10, 2019, 02:55:47 am »

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!
 

Offline vsmith

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Re: HP8596E Spectrum Analyzer repair
« Reply #53 on: October 18, 2019, 11:08:19 am »
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
 

Offline james_s

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Re: HP8596E Spectrum Analyzer repair
« Reply #54 on: October 18, 2019, 03:27:30 pm »
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.
 

Offline vsmith

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Re: HP8596E Spectrum Analyzer repair
« Reply #55 on: October 18, 2019, 05:38:59 pm »
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.
 

Offline james_s

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Re: HP8596E Spectrum Analyzer repair
« Reply #56 on: October 18, 2019, 06:18:53 pm »
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.
 

Online SilverSolder

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Re: HP8596E Spectrum Analyzer repair
« Reply #57 on: October 18, 2019, 06:40:49 pm »

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

Well done.  8)
 

Offline vsmith

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Re: HP8596E Spectrum Analyzer repair
« Reply #58 on: October 18, 2019, 09:55:26 pm »
@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.
 

Offline james_s

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Re: HP8596E Spectrum Analyzer repair
« Reply #59 on: October 18, 2019, 11:56:54 pm »
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.
 

Offline Renate

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Re: HP8596E Spectrum Analyzer repair
« Reply #60 on: October 20, 2019, 04:59:02 pm »
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?
 

Offline analogRF

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Re: HP8596E Spectrum Analyzer repair
« Reply #61 on: October 21, 2019, 02:34:40 pm »
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
 

Offline james_s

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Re: HP8596E Spectrum Analyzer repair
« Reply #62 on: October 21, 2019, 02:54:28 pm »
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.
 

Online Miti

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Re: HP8596E Spectrum Analyzer repair
« Reply #63 on: November 18, 2019, 01:16:22 am »
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.
That big spark at power up was by design!
 

Online Miti

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Re: HP8596E Spectrum Analyzer repair
« Reply #64 on: December 04, 2019, 02:30:53 am »
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
That big spark at power up was by design!
 


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