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8566B PL1 Unlock, PL2 Unlock and Ref Unlock

 

Hello,?

I have the subject conditions that started this morning when I powered on my previously flawless 8566B.? I had used it with an external ref for a while, had flipped it back to internal and it had been working OK for several weeks?until posting these errors this morning.? They are blinking so it seems to be on the borderline.? Is this an internal ref adjustment?? Thoughts?? Should I try an external reference?

Thanks


 

First try the external reference again, to be sure whether the internal one is OK or not. In my experience, the (Ovenaire brand as I recall) OCXOs used in the 8566s have been quite unreliable (ovens crap out), unlike the good old HP-made ones. It may be the application environment rather than the part being inadequate, however. As I have mentioned before, I don't like that the OCXO sits right in the high-flow center air plenum, so its oven has to work very hard to keep it hot while running.

Ed
 

Thanks, I'll try the? external ref.?

I have a 3586b sitting next to it and that has?the 10Mhz Oven in it.? Maybe I can just run that in?

I haven't checked the 3586B?output and the input into the 8566B and?will before testing.

Jerry
 

I tried an external reference without luck.? I guess it is time to dig into the problem.
 

On my 8566B, I found that I have little or no output from the 100Mhz cal signal as well.? I haven't lifted the unit out of the rack yet, but to be clear, I have a blinking PL1 Unlock, PL2 Unlock and REF Unlock as well as the missing 100Mhz.? Actually, the 100Mhz seems to be there but won't drive a 50ohm load at all.

I'll check the voltages today.? By the way, I hope I need something specialized to fix this beast as I always enjoy a purchasing opportunity.? I have 2 x 8568Bs, lots of scopes and voltmeters, signal generators, etc.? What else could I need?

Any input?

Thanks
 

I opened up my 8566B and found that the +12v on the A17 board to be reading 9.5V with 4.5 of AC ripple.??? The fuses on this board are ok.? No burning ext.

Should I just find a used board?? Is this board used in any others like the 8568b?

Thanks again.
 

Changing the board won't help unless the raw supply filter cap for that supply happens to be on it. You likely just need to find and replace the cap and it should be good to go. I believe the cap is chassis mounted, or on the motherboard, or on a separate assembly along with some others.

?

Ed
 

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Hi,
this looks like a power supply problem ;-)
I would invest a few hours on searching for the problem. If it is in the power supply, it is likely that you can fix it relatively easy. I would guess a bad capacitor or voltage regulator.
You can always get a new board, but first you should try to figure out what board you really need. I would be surprised if the problem is on A17.
Check the power supply and all other voltages before thinking about getting new boards!

Tobias


-------- Original message --------
From: "jehancoc@... [hp_agilent_equipment]"
Date: 10/21/17 21:08 (GMT+01:00)
To: hp_agilent_equipment@...
Subject: [hp_agilent_equipment] Re: 8566B PL1 Unlock, PL2 Unlock and Ref Unlock

?

I opened up my 8566B and found that the +12v on the A17 board to be reading 9.5V with 4.5 of AC ripple.??? The fuses on this board are ok.? No burning ext.

Should I just find a used board?? Is this board used in any others like the 8568b?

Thanks again.
 

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Check the power supplies and replace the bad filter capacitors.

Glenn

On 10/21/2017 3:07 PM, jehancoc@... [hp_agilent_equipment] wrote:
I opened up my 8566B and found that the +12v on the A17 board to be reading 9.5V with 4.5 of AC ripple.??? The fuses on this board are ok.? No burning ext.

Should I just find a used board?? Is this board used in any others like the 8568b?

Thanks again.

-- 
-----------------------------------------------------------------------
Glenn Little ETCS(SS) USN Ret, ARRL Technical Specialist,  SBE ARRL TAPR
Amateur Callsign:  WB4UIV            wb4uiv@...    AMSAT LM 2178
QTH:  Goose Creek, SC USA (EM92xx)  USSVI, FRA, NRA LM  QCWA  LM 28417 
"It is not the class of license that the Amateur holds but the class 
of the Amateur that holds the license"
---------------------------------------------------------------------------

 

Yes, I spoke too quickly about replacing the A17.? The regulator is off board on what I think is called the A23.? I'm trying to find the filter cap for the input to that regulator now but the schematic is hard to read.
 

So the filtered feed to the 12V comes off the cap that also feeds the 20V supply.? I have around 30V coming off that cap into the 12V regulator.? The output of the 12V regulator is only 9.5V.

So I guess I can start by replacing the regulator which looks like a job.

Thanks for the input.
 

Glen, it could be a bad cap on the -10V as the voltage is lower than it should be and of all the caps, that is where I see 4.6V of AC.? I'm going to take it out and bridge in a cap that I have in that range.? It strange that it is showing up in the 12V supply but I guess since the reference voltage is hosed it could be the issue.

It's almost always a cap.

Thanks

Jerry
 

OK, so the award goes to Glen to who called it correctly.?

Though the problem manifested itself as low 12V, the issue was in the -10V supply.? This caused a 120Hz pulse in the -5.6V (approx.)?voltage to the reference circuit?for the 12V regulator.? I didn't have the correct cap but I swapped in a 4,000uf (13,000uf required) and up it came albeit with noise sidebands from the lack of filtering.

So where can I find a MEPCO/CENTRALAB 13,000UF 25Vdc 30 surge cap?

Thanks for all the help.?

Jerry
 

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Does this look like the part?



The price seems reasonable.

Glenn


On 10/21/2017 7:41 PM, jehancoc@... [hp_agilent_equipment] wrote:
OK, so the award goes to Glen to who called it correctly.?

Though the problem manifested itself as low 12V, the issue was in the -10V supply.? This caused a 120Hz pulse in the -5.6V (approx.)?voltage to the reference circuit?for the 12V regulator.? I didn't have the correct cap but I swapped in a 4,000uf (13,000uf required) and up it came albeit with noise sidebands from the lack of filtering.

So where can I find a MEPCO/CENTRALAB 13,000UF 25Vdc 30 surge cap?

Thanks for all the help.?

Jerry

-- 
-----------------------------------------------------------------------
Glenn Little ETCS(SS) USN Ret, ARRL Technical Specialist,  SBE ARRL TAPR
Amateur Callsign:  WB4UIV            wb4uiv@...    AMSAT LM 2178
QTH:  Goose Creek, SC USA (EM92xx)  USSVI, FRA, NRA LM  QCWA  LM 28417 
"It is not the class of license that the Amateur holds but the class 
of the Amateur that holds the license"
---------------------------------------------------------------------------

 

Yes, looks like it.? They only come in a few sizes and bolt patterns.

I found the actual part in the UK on ebay.? It is a Mepco/Centralab 0180-0452 as in:


?

I sent him a note but purchased the ones in your prior reply.? Nothing to loose at that price.

Thanks.
 

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The one that you found is marked with a HP part number and was made in 1986.

If you have an ESR meter, I would be interested in knowing the capacitance, ESR and leakage of the failed part.

You might want to check the ones that you ordered to ensure that they are in fact good, as advertised.

Glenn

On 10/21/2017 8:39 PM, jehancoc@... [hp_agilent_equipment] wrote:
Yes, looks like it.? They only come in a few sizes and bolt patterns.

I found the actual part in the UK on ebay.? It is a Mepco/Centralab 0180-0452 as in:


?

I sent him a note but purchased the ones in your prior reply.? Nothing to loose at that price.

Thanks.

-- 
-----------------------------------------------------------------------
Glenn Little ETCS(SS) USN Ret, ARRL Technical Specialist,  SBE ARRL TAPR
Amateur Callsign:  WB4UIV            wb4uiv@...    AMSAT LM 2178
QTH:  Goose Creek, SC USA (EM92xx)  USSVI, FRA, NRA LM  QCWA  LM 28417 
"It is not the class of license that the Amateur holds but the class 
of the Amateur that holds the license"
---------------------------------------------------------------------------

 

The failed cap has an ESR of 56.32k and slowly dropping.? The capacitance is 48.78nF and rising.? This was measured with an Agilent 1733C.? I have an HP bench unit down in the lab so I'll walk down later but generally it agrees with this little handheld I wonder why I still have it.

The Mallorys were worth trying for the price.? I did find brand new Mallorys later today for $12.? But with ebay, you never really know what you get when they have more than one.

The weird thing is the way this thing failed. I never thought about switching an LM317K regulator on and off like that by pulsing the ref pin.? ?So the -10v supply is used to set the reference for the 12V supply and because this cap was bad, the -10V was pulsing up and down at 12Hz switching the 12v off and on.??
 

This goes to show the importance of not relying on DC measurements alone - always check supplies with a scope if something is suspicious. Meter measurements alone won't show ripple and other flakiness - they just average out whatever waveform is there.

?

Ed

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