Author Topic: Valhalla 2701C schematics?  (Read 1148 times)

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Offline forrestc

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Valhalla 2701C schematics?
« on: March 24, 2017, 09:38:59 AM »
I'm in the process of trying to repair of Valhalla 2701C.   At this point, I have lots of theories about what might be wrong with this, based on the description in the manual.

Unfortunately all of the manuals I can find (of various vintages) are lacking (but refer to) the schematics of this product.   I'm hoping someone here has a copy of them or knows where I can find them.

Any ideas?

Thanks.

-forrest
 

Offline JFJ

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Re: Valhalla 2701C schematics?
« Reply #1 on: March 24, 2017, 08:01:46 PM »
If you can't find a manual with schematics to download, then Artek can provide one on CD-ROM:

http://www.ebay.com/itm/Valhalla-2701C-DC-Voltage-Calibrator-Operating-Service-Manual-/371715601232

The manuals that I've had from them have been top quality scans (300 DPI text, 600 DPI schematics).
 
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Offline alm

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Re: Valhalla 2701C schematics?
« Reply #2 on: March 24, 2017, 11:12:31 PM »
You can also order directly from his website. Saves you $1 and should be faster.
 
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Offline forrestc

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Re: Valhalla 2701C schematics?
« Reply #3 on: March 25, 2017, 07:16:04 AM »
Ended up buying one from artek... and it has everything I need.

Apparently the HV supply is AWOL in this, still trying to narrow it down to the specific Part(s).   Slow going since it's a potentially a 1000V supply and I have no desire to experience 1000V coursing through my body.

 

Online Edwin G. Pettis

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Re: Valhalla 2701C schematics?
« Reply #4 on: March 28, 2017, 04:00:36 AM »
Hi forrestc,

Do you know about how old this unit is?  I also have a 2701C unit, the auto-zero op-amp that controls the high voltage regulator was out to lunch, mine is from the mid-80s.
 

Offline forrestc

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Re: Valhalla 2701C schematics?
« Reply #5 on: March 28, 2017, 04:41:05 PM »
Hi forrestc,

Do you know about how old this unit is?  I also have a 2701C unit, the auto-zero op-amp that controls the high voltage regulator was out to lunch, mine is from the mid-80s.

Mid-80's as well, apparently (based on date codes).  It has Bipolars instead of fets for the output chain, so it's an earlier unit apparently.

I believe I found the fault - the HV supply has about 4-5 450V electrolytics.  I finally dug out the ESR meter and discovered one was horribly out of whack (the ESR meter refused to acknowledge it was even a capacitor - which means and extremely high ESR).   I have exact replacements on the way for the entire set, plus others of a similar age in the unit.   We'll see if that fixes it.     I'm fairly comfortable that it will, especially since I was measuring something like 35V ripple across the caps - not exactly any filtering going on.  Wish I would have measured this first, especially since I have had no shortage of bad electrolytics being the cause of problems over the years.

It just occured to me I should also measure the rectifier diodes to make sure they're not shorted before I put those caps in, just in case.....

I'll know sometime next week hopefully.

-forrest
 

Online Edwin G. Pettis

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Re: Valhalla 2701C schematics?
« Reply #6 on: March 29, 2017, 09:48:24 AM »
If your unit has a bunch of yellow precision wire wound resistors in it like mine, those were made by our previous company which made all of the precision WWs for Valhalla at the time.  It has now morphed into Ultrohm Plus years later.
 

Offline forrestc

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Re: Valhalla 2701C schematics?
« Reply #7 on: March 29, 2017, 01:40:12 PM »
If your unit has a bunch of yellow precision wire wound resistors in it like mine, those were made by our previous company which made all of the precision WWs for Valhalla at the time.  It has now morphed into Ultrohm Plus years later.

Yeah, if you mean these yellow ones which at first glance one would assume were old capacitors, yep it's full of them.   

Looks like my replacement caps will be here tomorrow - unfortunately I'm headed out of town thursday so I'm not sure I'll get to them before I have to get ready to leave.
 


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