Author Topic: HP8596E Spectrum Analyzer repair (Read 7874 times)

KCT_99 · « **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 ?

pbarton · « **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.

KCT_99 · « **Reply #2 on:** September 30, 2019, 08:04:01 pm »

Many BIG THANKS for your kind help !

Miti · « **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.

KCT_99 · « **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.

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.

TheSteve · « **Reply #5 on:** October 01, 2019, 07:54:57 pm »

Maybe time for an LCD upgrade

KCT_99 · « **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.

KCT_99 · « **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 ?

Miti · « **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.

SilverSolder · « **Reply #9 on:** October 02, 2019, 05:42:37 pm »

Quote from: KCT_99 on October 02, 2019, 12:03:30 am

... 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.

KCT_99 · « **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.

KCT_99 · « **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 ?

SilverSolder · « **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...

KCT_99 · « **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.

SilverSolder · « **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...

KCT_99 · « **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.

SilverSolder · « **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...

james_s · « **Reply #17 on:** October 06, 2019, 05:26:01 am »

Quote from: KCT_99 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.

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.

SilverSolder · « **Reply #18 on:** October 06, 2019, 11:35:03 am »

Is there a circuit diagram for this thing?

KCT_99 · « **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 ?

james_s · « **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.

KCT_99 · « **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.

SilverSolder · « **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.

KCT_99 · « **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.

james_s · « **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?


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Author Topic: HP8596E Spectrum Analyzer repair (Read 7874 times)

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