Author Topic: HP Spectrum Analyzer 851D Display 8551D RF Unit  (Read 402 times)

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Offline Radio Tech

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HP Spectrum Analyzer 851D Display 8551D RF Unit
« on: February 15, 2019, 05:35:25 pm »
A while back a viewer drove up and delivered this old HP spectrum analyzer to me.  This weighs a ton so shipping would have been crazy.
Good thing it was donated so I have nothing in it.

I do not do many  repair threads. usually just videos. But I want to document the repair in a thread along with videos on YouTube. I have one video on this already.
It is #199 https://www.youtube.com/theradioshop

 I have not set a time to start this repair as it will most likely be lengthy.  So this is going to take a long time between other normal repairs in the shop.
I do think the first order of business on this unit is get it cleaned up. Thing is very dirty as it appears to have set in a garage on a concrete floor for some time.
Although in the video I did manage to get the display unit to come on and show a trace.  All I did was replace two bad capacitors that was easy to spot. After that the display had a nice crisp trace.

So I will start with tearing the RF deck apart, clean, and then start by pulling each board and replacing out of spec components.  There is a lot of discolored resistors and most likely more bad capacitors.  I also going to have to do a lot of studying on this circuit so I can find my way around it.  One thing I noticed is the online manuals are a bit different than the way the unit is built. Specially the RF deck.  The manual shows the HV timing circuit on a plug in PCB.  This unit does not have that board and the relays and components are chassis mounted.  Perhaps I need to find an original manual.

Serial numbers:
Display unit - 813-02273
RF unit - 823-02266

Below is some low res pictures of the unit.




















« Last Edit: February 15, 2019, 05:40:37 pm by Radio Tech »
 

Offline AF6LJ

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Re: HP Spectrum Analyzer 851D Display 8551D RF Unit
« Reply #1 on: February 15, 2019, 09:19:38 pm »
Power supply issues are not uncommon with these units considering their age.
Sue AF6LJ
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Offline Radio Tech

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Re: HP Spectrum Analyzer 851D Display 8551D RF Unit
« Reply #2 on: February 15, 2019, 11:38:15 pm »
Power supply issues are not uncommon with these units considering their age.

Thanks for that tip Sue. Going to need a lot of tips on this one.  I printed the manuals for both units. That should give me some good reading material to get to know them.  The RF deck manual was 2.5 inches thick.

Offline AF6LJ

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Re: HP Spectrum Analyzer 851D Display 8551D RF Unit
« Reply #3 on: February 21, 2019, 11:08:51 pm »
Power supply issues are not uncommon with these units considering their age.

Thanks for that tip Sue. Going to need a lot of tips on this one.  I printed the manuals for both units. That should give me some good reading material to get to know them.  The RF deck manual was 2.5 inches thick.

I use to have to printed manuals origanials and they went with my 851/8551 when I finally got rid of it.

/Sue heads off looking for a decent online copy to play along with.
Sue AF6LJ
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Offline Radio Tech

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Re: HP Spectrum Analyzer 851D Display 8551D RF Unit
« Reply #4 on: February 23, 2019, 03:28:34 pm »
Trying to find someone that has an original manual to see if it is like the unit I have.  So far no luck.
Really want the manual identical to mine. Will make troubleshooting a easier to follow along with.
I got the unit moved over to the other bench now so I can start taking it apart to clean and rebuild boards.
All I need is more time....


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