Hi!
Does anyone have full schematics for older 2701 or 2701B? I cannot even find pictures of the boards of the oldest model.
Wictor
Hi!
Does anyone have full schematics for older 2701 or 2701B? I cannot even find pictures of the boards of the oldest model.
Wictor
Check with http://artekmanuals.com/manuals/other-manuals/ -- he responded quickly when I asked if what he had on the 2701c contained the LNF variant (it did not). He lists the 2701A/B/C.
I have a PDF op/service manual for the 2701C which Valhalla gave to me a few years back. It mentions the -LNF option but gives no circuit details. PM me if you can use it.
At least you have the GPIB option. Would be interesting to see what happens on the display at power up if you remove the header ribbon connector before hand.
I have a PDF op/service manual for the 2701C which Valhalla gave to me a few years back. It mentions the -LNF option but gives no circuit details. PM me if you can use it.The manual I have , and have attached here, also mentions this option but has no further detail either . What I find odd is that Valhalla themselves say they don't have the details.
Or some one couldn't be bothered hunting through a filing cabinet
Valhalla was not known for using 'special' components, the vast majority of the components in their instruments were standard off-the-shelf even if they had in-house numbering on them. During the period we were making all of their PWW resistors, I do not recall a LNF option in the 2701C models in production at the time. This 'option' may have been a 'special' done for a particular customer at some time before the 'C' version and the instrument you have come by may have been somebody's attempt at bodging an LNF into the unit. I have a 2701C manual from Valhalla and first chance I get, I'll take a look at it and see if there is anything in it about this option.
The serial# sticker on the outside says "2701C-LNF" for what it's worth. The only other reference I found to LNF (other than ebay scrapers), is an index of content in use at Sandia National Labs in the recent past. It lists both a 2701C and a 2701C-LNF in their possession.
I have a couple 2701C's here in the repair pile, I'll look and see if either of them are LNF's.QuoteThe serial# sticker on the outside says "2701C-LNF" for what it's worth. The only other reference I found to LNF (other than ebay scrapers), is an index of content in use at Sandia National Labs in the recent past. It lists both a 2701C and a 2701C-LNF in their possession.
That makes sense. I tested that unit when it was offered for sale and decided to pass on it. You must have bought it on eBay from "solanotraders", an aggressive eBay flipper. I would advise you to assume that almost anything you buy from him has significant issues. I attend the same industrial auctions he does, and it is part of my job to make sure he doesn't get TE stuff that works
Neither of my 2701C's are -LNF's...
Trade you one Rare^WVintage^Unique -LNF for a working 2701C in your pile? :-)
Please note this binary file is for the 2701c with NO current option. Also the unit does not have the GPIB option either but I'll wager the firmware contains that function and does a check at power on.
The sticker covering the UV EPROM has fallen off (and since replaced with some electrical tape) so I don't know what FW version is on my instrument, but I can read the ROM and copy it to the forum if anyone is interested.
yeah, would really like to see the fully fledged FW of this thing. mine doesn't have the current source option and i'm hesitating to retrofit the current source option w/o knowing whether the FW could actually support it.
as for the churned bleeder resistors in your unit, that issue may point at some problem in the pre-regulator on the primary side. could be that the HV DC bus was always at max voltage, regardless of the selected range. you can check that by measuring the voltage across the entire series regulator chain. should be constant at some 240 VDC with the instrument set to 0 VDC at any range.
The bleeder resistors in the 2701C have clearly a too low power rating. It makes one wonder if no basic design checks of dissipation were made by Valhalla. Check out my unit at https://dabbledoo.weebly.com/valhalla-2701c.html where I replaced the original resistors with ROX5S from TE Connectivity, rated at 5 W.
The larger power rating by itself is not the reason why changing the resistors is a good idea: Physically larger resistors have a larger surface area and this a good property if you want to mitigate a hot spot.