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Re: HP 8566B - Can my high voltage transformer be faulty?

 

The PDA supply MUST be stable and regulated or the size of the CRT image will keep changing, Also not a good idea to operate long term without load on high voltage winding of the HV transformer.

If it is impossible to find the correct HV multiplier it may help to look for a Tektronix CRT scope one, my guess and it is only a guess without measuring the HV transformer output is that it is a X6 one.

G Edmonds
On Thursday 11 July 2024 at 15:52:48 BST, Dave Me <scope.project@...> wrote:


Idea.
?
The flyback and HVM simply make a high DC voltage and low current (milli-ampere"?)
?
Maybe this to replace a difficult to find HVM? Adjustable HV-DC output:
?
amazon DOT com/Adjustable-Voltage-Electrostatic-Precipitator-Supply/dp/B0B4ZVG3B8
?
This would assume the sweep of the flyback is still working to drive the yoke - coils or deflection plates.
?
11.07.2024, 01:09, "saevar" <saevartj@...>:

Hi George,

I couldn't wait so I tested the method you suggested immediately and you were absolutely right. There appears a small green "window" visible (like a miniature image) on the CRT in the center and the fuse is not blown. I am thoroughly impressed.
Thanks so much!

Regards
Saevar
Re: HP 8566B - Can my high voltage transformer be faulty?

Dave Me
 

Idea.
?
The flyback and HVM simply make a high DC voltage and low current (milli-ampere"?)
?
Maybe this to replace a difficult to find HVM? Adjustable HV-DC output:
?
amazon DOT com/Adjustable-Voltage-Electrostatic-Precipitator-Supply/dp/B0B4ZVG3B8
?
This would assume the sweep of the flyback is still working to drive the yoke - coils or deflection plates.
?
11.07.2024, 01:09, "saevar" <saevartj@...>:

Hi George,

I couldn't wait so I tested the method you suggested immediately and you were absolutely right. There appears a small green "window" visible (like a miniature image) on the CRT in the center and the fuse is not blown. I am thoroughly impressed.
Thanks so much!

Regards
Saevar
Re: Checking HP 8672A output level: are these drops normal?

Dave Me
 

I do not know this instrument. I assume the path of amplifier is 50 ohms?

A suggestion on "checking power level" is to use a microwave detector diode (of the type like BAT1504) and a short coaxial RG 174 cable to connect to an accurate DVM.

? The newer microwave diodes have extremely low capacitance (i.e. 0,3 pF and lower). Some in special packages have < 0,1 pF, with strip line terminations.

I would suggest to make a micro stripline of FR4 single side copper plane with 1/4 inch wide strip of also FR4 as the strip. Exact dimensions on Pasternack website micro stripline calculator. Put the diode on a cut in the strip (series).

The short RG 174 cable provides some 10's of pF for the output filtering. I also put a small ceramic trimmer of up to 40 pF for lower frequencies to tune the detector.

These diodes are very, very sensitive to reverse voltage, may be ~ 4 V.

Note to not test them with a DVM diode test which may be 10V O.C.

Put several diodes in series to increase reverse voltage and lower capacitance. These diodes have extremely low forward voltage drop at micro-ampere currents (i.e. 10s of mV).

Terminate the micro strip line in a microwave resistor. SMA connectors can conveniently solder to the micro strip line.

The micro strip configuration is inherently self shielding (but not perfect).
Re: HP 8341B Firmware Questions

 

For the records:
I have an HP8340A with firmware rev. 23 of May 1985, serial prefix 2602A, which works flawlessly with my HP8510C firmware 7.14 of August 1998.

Tom
Re: HP 8341B Firmware Questions

 

¿ªÔÆÌåÓý

Hi,

My prefix is 2928A so later than that. It mentions a "minimum of bugs" so I'm not sure which bugs the May 88 firmware might lead to, but I have not noticed any problems.

Best regards,
Job

On 11-07-2024 00:41, saevar wrote:

Hi Job,

Thanks for the reply. That's great to hear, I was a bit worried since I only have the May88 version as well.

FYI, I got this is info from the 8510C Service quick reference guide (see the last paragraph):
Re: Checking HP 8672A output level: are these drops normal?

 

Back to repairing the 8672A
The indicator lights are now all repaired but the low output level problem is still there.?
It would be nice to be able to check the output level of the power amplifier as I know the input level is good and if the output power is OK the problem must be in the YTM however the mechanical construction of the device makes it very difficult to disconnect at either points A, B or C


Is there any recommendation on how to check the output of the power amp?

Re: HP 8341B Firmware Questions

 

Hi Job,

Thanks for the reply. That's great to hear, I was a bit worried since I only have the May88 version as well.

FYI, I got this is info from the 8510C Service quick reference guide (see the last paragraph):
Re: HP 8566B - Can my high voltage transformer be faulty?

 

Hi George,

I couldn't wait so I tested the method you suggested immediately and you were absolutely right. There appears a small green "window" visible (like a miniature image) on the CRT in the center and the fuse is not blown. I am thoroughly impressed.
Thanks so much!

Regards
Saevar
Re: HP 8566B - Can my high voltage transformer be faulty?

 

FWIW, I had a very similar problem with my 3585B spectrum analyzer. I¡¯m my case the flyback had shorts. The circuits are very similar and the supply fuse (18V) would blow on power up. ?You can do a simple ring test with a signal generator and oscilloscope plus a few components (resistor/cap). You don¡¯t need a dedicated ring tester for a one off test. Mine had shorts and failed the ring test. Ended up having to find a replacement flyback from a parts unit. It might be worth to test if you haven¡¯t confirmed the HV multiplier and certainly before you buy replacement parts. You will have to remove the flyback from the unit to test it though.
Re: HP 8566B - Can my high voltage transformer be faulty?

 

Hi again Saevar

I should add that if the HV multiplier has failed the oscillator will not be able to start and will draw a high current due to the load on it, it will then blow the safety fuse, just what you are seeing.

G Edmonds

On Wednesday 10 July 2024 at 21:38:06 BST, saevar <saevartj@...> wrote:


Hi all,

Thanks for your valuable advice.
George, what makes you conclude that the A1A11 is faulty?

I am not that familiar with CRT circuitry and am therefore a bit lost as to how to test these various parts (without risking my health), i.e. ringing test and how to excite the main winding with an RF oscillator as Dave mentions. Any further advice is much appreciated.

To make it more clear what is faulty is, the overview figure below shows the display circuits. On the far left is the A1A6 and in the center is A1A3 high voltage regulator.
The HV oscillator does not oscillate and the fuse at the 23V supply is blown every time.?



The HV oscillator is shown in more detail in the images below with the Q7 transistor, who's collector and the 23V supply are connected to one of the primary transformer coils.
The Base and the output of the OSC drive are connected to another transformer coil for feedback.
Re: HP 8566B - Can my high voltage transformer be faulty?

 

Hi Saevar

Experience, experience and experience. I have been repairing oscilloscopes now for almost 65 years. Rule one, the higher the operating voltage the more likely to fail also frequently the high voltage multiplier fails when an instrument is put back into use after not being used for some time.

The high voltage multiplier takes the high voltage from the HV transformer which is probably about 3KVAC and multiples it up to the PDA voltage of 18KVDC. It is actually a Cockcroft and Walton multiplier, Google this.

I am not familiar with this SA but you should find that the HV multiplier has three connections one of which will be a thick high voltage cable that goes directly to the CRT, a ground and an input from the HV transformer.

Locate the wire from the HV transformer and disconnect it from the HV multiplier. Well insulate this wire as it will have 3KVAC at a minimum on it.

Replace the fuse and switch the instrument on, if the fuse does not blow the problem is the HV multiplier. You may even get a CRT trace that is defocused .

Let me know what you find.

G Edmonds


.

On Wednesday 10 July 2024 at 21:38:06 BST, saevar <saevartj@...> wrote:


Hi all,

Thanks for your valuable advice.
George, what makes you conclude that the A1A11 is faulty?

I am not that familiar with CRT circuitry and am therefore a bit lost as to how to test these various parts (without risking my health), i.e. ringing test and how to excite the main winding with an RF oscillator as Dave mentions. Any further advice is much appreciated.

To make it more clear what is faulty is, the overview figure below shows the display circuits. On the far left is the A1A6 and in the center is A1A3 high voltage regulator.
The HV oscillator does not oscillate and the fuse at the 23V supply is blown every time.?



The HV oscillator is shown in more detail in the images below with the Q7 transistor, who's collector and the 23V supply are connected to one of the primary transformer coils.
The Base and the output of the OSC drive are connected to another transformer coil for feedback.
Bubble Memory Reseed

 

Hi All,
To reseed the bubble memory on the HP3561A DSA, a special 'reseed module' is required. It was probably made by Intel.
Has anyone done this successfully and know where the reseed module can be obtained?

I asked this some time ago, but haven't resolved the problem.

Thanks,
John
Re: HP 8566B - Can my high voltage transformer be faulty?

 

Hi all,

Thanks for your valuable advice.
George, what makes you conclude that the A1A11 is faulty?

I am not that familiar with CRT circuitry and am therefore a bit lost as to how to test these various parts (without risking my health), i.e. ringing test and how to excite the main winding with an RF oscillator as Dave mentions. Any further advice is much appreciated.

To make it more clear what is faulty is, the overview figure below shows the display circuits. On the far left is the A1A6 and in the center is A1A3 high voltage regulator.
The HV oscillator does not oscillate and the fuse at the 23V supply is blown every time.?



The HV oscillator is shown in more detail in the images below with the Q7 transistor, who's collector and the 23V supply are connected to one of the primary transformer coils.
The Base and the output of the OSC drive are connected to another transformer coil for feedback.
Re: HP 8566B - Can my high voltage transformer be faulty?

 

And 15,734 Hz in the US (NTSC).

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
420 Via Palou Mall
Stanford University
Stanford, CA 94305-4070

On 7/10/2024 7:57 AM, Dave_G0WBX via groups.io wrote:
Or 15.625kHz in the UK.

Dave B.
Re: For HP 8660 Power Supply Load Question please?

Dave Me
 

Thanks! very good. The ~ 17 ohms is the lamp and dropping resistor? inside the manual fine tune encoder. Im seeing another 10 ohms cold load thru the Gpio boards apparently to or from the Xtal Oven oscillator.

Just wanting to verify it is not a circuit fault as some fault caused G-K shorting of the 5.25 v protect SCR. It might just be a bad SCR.
Re: HP 5086-7842 Attenuator - max input power

 

This should give you the information you need.

Steve

Agilent HP 33320 series attenuators datasheet.pdf
Agilent HP 33320 series attenuators datasheet.pdf

Re: For HP 8660 Power Supply Load Question please?

 

Hi Dave,

Just checked my 8660C s/n 03700 something.? ? ?I measure 16.2 ohms to the chassis.? ?My 8660 has and 8660D power supply.....long story.? ?

I have not unplugged and removed from a rack my 8660 in about 20 years!?

92 means a wire colored white-red (white with a red stripe I guess).? ? HP used the standard color code on wiring.? ? Red usually meant a positive voltage with respect to chassis, black chassis,? violet a negative voltage with respect to the chassis, etc..?
??
I repaired the last 8660 and plug-ins before the eastern region repair center became a calibration-only hub and consolidated the full service centers to Roseville CA.? ?At one time we had maybe 50-60 techs.? ? ??

I continue to work on HP instruments as a volunteer at the Antique Wireless Assoc. in Bloomfield, NY.? ? Haven't seen any 8660's come thru as donations from estates but plenty of 8640s.? ?Also just fixed up an HP410B and before that an HP 204 (or 209).? ? Now retired (from Harris).? working on the old HP instruments has been a blast from the past after working for HP for >24 years.? See plenty of other old common HP units.? ?

??
Re: HP 5086-7842 Attenuator - max input power

 

Thank you Robert and Don,

Fortunately the device does have 24VDC written on it, so I can be sure of that spec. +30dBm continuous suits me well, I stay firmly under +10dBm or so in my experiments.

John.
Re: HP 8566B - Can my high voltage transformer be faulty?

 

Hi

From the information given and the method of failure it is almost certain that the A1A11 high voltage multiplier that provides the PDA (CRT Post Deflection Acceleration) voltage has failed. This is a common problem with CRT displays. It is just possible that the A1A3 high voltage transformer has failed but this is very unlikely. To check the high voltage transformer it is necessary to do a ringing test on it.

Be very careful around the CRT high voltage section as there is 4KV present in a number of places and the PDA voltage is some 18KV.

G Edmonds

On Wednesday 10 July 2024 at 15:57:48 BST, Dave_G0WBX via groups.io <g8kbvdave@...> wrote:


Or 15.625kHz in the UK.

Dave B.
Re: HP 8566B - Can my high voltage transformer be faulty?

Dave Me
 

Oh! Yes. PAL. Everything in the world is not according to U.S. standards (NTSC= naught twice the same colour)

There was an equipment " flyback tester" for such purpose but that TV tool might not suffice for this small CRT system if at a different frequency, it need not necessarily be 15 KHz, it could be many frequencies.

But due to relaive high value of test equipment it could be worth try to " ring" the system.
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