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 Post subject: Re: Restoration of HP141s/8553L/8552A
PostPosted: Jan Tue 29, 2019 8:05 pm 
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I think I read a thread on here from a while back or maybe an HP bulletin... the fuses blow sometimes because of a rectifier tube in there not always firing ?? I believe it is a mini wire lead type. Don't trust my memory but I think part of the fix was replacing them with a Zener .... did I say not to trust my memory? Search for it, should be either online or on the forum

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 Post subject: Re: Restoration of HP141s/8553L/8552A
PostPosted: Jan Tue 29, 2019 8:48 pm 
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I seem to remember reading something to that affect fairly recently too. Can't for the life of me remember where nor exactly when, but within the last few months I'm sure.

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 Post subject: Re: Restoration of HP141s/8553L/8552A
PostPosted: Jan Tue 29, 2019 9:57 pm 
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It's been discussed on the HP/Agilent equipment group, formerly on Yahoo Groups and now on groups.io, around February 2018. The symptom is fuses blowing in the plug-ins at power-up. The cause is aging of V1, a voltage regulator tube. Due to aging, it takes longer to strike at start-up, leading to momentary overvoltage on the power supply rails at startup. The overvoltage spike then trips a crowbar circuit in the plugins, blowing the fuse.

Later versions of the 141T power supply used a zener instead of the VR tube.

Dave Wise posted a circuit that replaces the VR tube with a zener and a TL431.

If you are a member of the group, this link will take you to Dave Wise's photo album on the subject:
https://groups.io/g/HP-Agilent-Keysight ... m?id=68333
The thread is entitled "141T reference replacement", search for that on groups.io.

If you're not a member and don't want to join, someone else has a copy of the circuit:
Image

the location of V1 on the PCB:
Image

and the location of V1 on the schematic:
Image

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 Post subject: Re: Restoration of HP141s/8553L/8552A
PostPosted: Jan Wed 30, 2019 4:55 am 
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There is a NOS one of those regulator tubes in the classifieds right now.

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 Post subject: Re: Restoration of HP141s/8553L/8552A
PostPosted: Jan Wed 30, 2019 12:57 pm 
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thank you Steve :)

possible I have a 80V Zener in the spareparts, there is some ZL and ZTX with higher voltages, will look after work.

Martin


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 Post subject: Re: Restoration of HP141s/8553L/8552A
PostPosted: Jan Wed 30, 2019 1:56 pm 
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I posted this fuse issue earlier in this discussion from the former HP/Agilent Yahoo group. Just go to page one.

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 Post subject: Re: Restoration of HP141s/8553L/8552A
PostPosted: Jan Wed 30, 2019 3:34 pm 
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There is a HV linear regulator that would work in place of the neon stabilizer just fine:
https://www.digikey.ca/product-detail/en/microchip-technology/LR8N3-G/LR8N3-G-ND/4902368
That LR8 in the TO92 case would take max 450V input voltage, 10mA output current, and 750mW dissipation.
Putting it into the circuit and setting it to 82V it would dissipate about 263mW.

Peter


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 Post subject: Re: Restoration of HP141s/8553L/8552A
PostPosted: Jan Wed 30, 2019 8:06 pm 
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flyboy71 wrote:
I posted this fuse issue earlier in this discussion from the former HP/Agilent Yahoo group. Just go to page one.

Sorry I didn't pick that up.

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 Post subject: Re: Restoration of HP141s/8553L/8552A
PostPosted: Jan Thu 31, 2019 9:13 am 
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ZL and ZTX are the german Zemer diode for power, they can dissipate some Watts with cooling.
I will test the temperature running updown of that
Have them in the spares box

Martin


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 Post subject: Re: Restoration of HP141s/8553L/8552A
PostPosted: Feb Fri 01, 2019 5:49 pm 
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so I have now a 8556A :wink:

Attachment:
141-21a.jpg
141-21a.jpg [ 212.57 KiB | Viewed 230 times ]


Attachment:
141-23a.jpg
141-23a.jpg [ 192.29 KiB | Viewed 230 times ]


now learning how to sweep a Audio Stage with that.

greetings
Martin


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 Post subject: Re: Restoration of HP141s/8553L/8552A
PostPosted: Feb Mon 04, 2019 9:16 am 
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the tarcking generator is far away from the center frequency,
there is adjust required


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 Post subject: Re: Restoration of HP141s/8553L/8552A
PostPosted: Feb Mon 04, 2019 10:55 am 
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They Both have front panel adjustments, and I would think there is more alignment / adjustment inside. You need to get the manuals. Maybe they are on BAMA, or surely they are at THE KEYSIGHT URL.

The 8444 and 8443 do not track down into the audio range. The '43 minimum frequency is 100Kc, and the '44 is 500Kc.

Image

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 Post subject: Re: Restoration of HP141s/8553L/8552A
PostPosted: Feb Mon 04, 2019 12:37 pm 
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hello Mike,
interesting parts for collecting :)
I means the internal tracking generator from the 8556A, that have to run the audio area.
Martin

p.s. about ZZ1000 stabi: it was manufactured by the germans also (Valvo, Siemens),
so they are in the bay around 8$


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 Post subject: Re: Restoration of HP141s/8553L/8552A
PostPosted: Feb Sun 10, 2019 6:35 pm 
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On the 8556A is written the 8552A must have a mod to use that.
Is it correct, I have a plate at back from 8552A "TG Mod" , is this meaned and allready in my 8552A installed or not?
TG can only be a tracking generator and 8556A is one what have it. The tracking generaor goes wrong, that must be adjusted all. But first I want to know if my IF have this Mos what is required

Martin


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 Post subject: Re: Restoration of HP141s/8553L/8552A
PostPosted: Feb Sun 10, 2019 7:24 pm 
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MM I think all the manuals are available for free download. I've got most if not all, so if you get stuck I can perhaps look something up or scan a page or two. Let me know. I'm watching with interest since I have the same system with all the plug ins and really haven't done more than play with it a bit.

bb

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 Post subject: Re: Restoration of HP141s/8553L/8552A
PostPosted: Feb Sun 10, 2019 8:32 pm 
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MM wrote:
On the 8556A is written the 8552A must have a mod to use that.
Is it correct, I have a plate at back from 8552A "TG Mod" , is this meaned and allready in my 8552A installed or not?
TG can only be a tracking generator and 8556A is one what have it. The tracking generaor goes wrong, that must be adjusted all. But first I want to know if my IF have this Mos what is required

Martin


http://www.arimi.it/wp-content/Strument ... Manual.pdf

For the 8552B SN prefixes 977 and below will need the mod
For the 8552A SN prefixes 991 and below will need the mod

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 Post subject: Re: Restoration of HP141s/8553L/8552A
PostPosted: Feb Sun 10, 2019 10:31 pm 
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Quote:
I have a plate at back from 8552A "TG Mod" , is this meaned and allready in my 8552A installed or not?
Yes, the modification should be in the 8552.

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 Post subject: Re: Restoration of HP141s/8553L/8552A
PostPosted: Feb Tue 12, 2019 5:13 pm 
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hello Mike,

I think I make a mistake by understanding how that works.
When I switch the 8556A to 0-30kHz it have to run a sweep from zero to 30kHz?
But the actually frequency is imho the center frequency, that can`t be 0Hz bec. left side is a half screen.
So the zero frequency have to be at left side, not in the middle? And the 30kHz then is in center or at the right side of the screen?

I have to adjust that apparatus so I must know that exactly.
Here is a precision LF generator with counter, I will use it for adjust the plugin.

greetings
Martin


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