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Electronics => Metrology => Topic started by: lowimpedance on December 21, 2017, 02:53:58 am

Title: Valhalla 2701c schematics + firmware V3
Post by: lowimpedance on December 21, 2017, 02:53:58 am
 After searching high and low there appears to be no schematics for the 2701c online. So having located a paper copy I will add here the schematics plus the parts lists and any other extra info that is not already uploaded, including a dump of the firmware, as I get the spare time.
To start with we have the Main PCB with the parts overlay and useful notes plus the relevant schematics.
Additional is the option I-T2 120mA option schematic.

One thing that I have not found answered yet is the firmware different for units with the current option installed or is it all the same and there is a jumper or link on the main PCB that tells the system it is present  :-//. A possible hint might be from the GPIB option where on the schematic there is a pin on the header connection to the main PCB, (pin 20), called IEEE FIT tied to 0V which pulls down a pin on a 6821, (pin 16 portb), when plugged in. So perhaps the firmware just checks a logic level for the current option too !.

Edit:1. added display and GPIB schematics + comp overlays.
       2. Had a good look on the main PCB and schematics and it looks like there is no test for the current option so its most likely a firmware difference, pity.
           I noted that the firmware from a 2701c with the current option was obtained but had not been uploaded, in this thread :
           https://www.eevblog.com/forum/metrology/tear-down-valhalla-2707a/msg941497/#msg941497 (https://www.eevblog.com/forum/metrology/tear-down-valhalla-2707a/msg941497/#msg941497)
           Would be nice to try the firmware for the current option one day !.



Title: Re: Valhalla 2701c schematics +..
Post by: lowimpedance on December 21, 2017, 02:55:57 am
 Mechanical drawings and Parts list.
Title: Re: Valhalla 2701c schematics +..
Post by: quarks on December 21, 2017, 02:06:42 pm
thanks a lot for sharing this documents

just in case anyone missed it, have a look at a very nice video from Shahriar Shahramian (aka Hugoneus) "The Signal Path"

https://www.eevblog.com/forum/testgear/teardown-repair-calibration-of-a-valhalla-2701c-programmable-precision-source/msg840669/#msg840669 (https://www.eevblog.com/forum/testgear/teardown-repair-calibration-of-a-valhalla-2701c-programmable-precision-source/msg840669/#msg840669)

https://www.youtube.com/watch?v=e-UwxRhYLS8 (https://www.youtube.com/watch?v=e-UwxRhYLS8)
Title: Re: Valhalla 2701c schematics +..
Post by: TiN on December 21, 2017, 05:05:58 pm
lowimpedance, we missed your threads indeed.  :-+
Title: Re: Valhalla 2701c schematics +..
Post by: lowimpedance on December 22, 2017, 02:14:20 am
Lastly we have the ROM firmware from the 2701c with bonus pic of the label and the programmer read showing the correct checksum as per the label  :-+.

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.
Displaying a "no IEEE" message during the startup test on the unit here. (must test that theory by shorting to 0V pin 20 on the header socket).
Title: Re: Valhalla 2701c schematics + firmware V3
Post by: jasonbrent on February 13, 2018, 05:37:14 pm
I've got a 2701c en route that I found on fleabay. I'm hoping it is reasonably functional. Calibration keys are available from Valhalla... $50 per set plus shipping.

Sent from my SM-N950U using Tapatalk

Title: Re: Valhalla 2701c schematics + firmware V3
Post by: texaspyro on February 13, 2018, 10:09:05 pm
I've got a 2701c en route that I found on fleabay. I'm hoping it is reasonably functional. Calibration keys are available from Valhalla... $50 per set plus shipping.

I took the cal switch out of a 2703 to my local locksmith... 10 minutes and $5 later, I had a set of keys,
Title: Re: Valhalla 2701c schematics + firmware V3
Post by: jasonbrent on February 14, 2018, 05:55:13 pm
I've got a 2701c en route that I found on fleabay. I'm hoping it is reasonably functional. Calibration keys are available from Valhalla... $50 per set plus shipping.

I took the cal switch out of a 2703 to my local locksmith... 10 minutes and $5 later, I had a set of keys,

I wish I'd thought of that. =) .. As an aside, I also asked them for a quote on refurbishment/repair if necessary; $2500 flat rate. While I don't expect to go down that route, it's good to know that they are still willing to rework very old gear. Given the price point of these new, that isn't horrible (but falls way outside of my comfort zone for hobby).
Title: Re: Valhalla 2701c schematics + firmware V3
Post by: lowimpedance on February 14, 2018, 10:52:37 pm
I've got a 2701c en route that I found on fleabay. I'm hoping it is reasonably functional. Calibration keys are available from Valhalla... $50 per set plus shipping.

Sent from my SM-N950U using Tapatalk

 Does the soon to arrive 2701c have the 'Current option' installed ?.
If yes would you be able to read the firmware if you have access to a programmer, and only if your comfortable doing so of course.
The required parts for the option are easy enough but unfortunately the firmware appears to be different so to retrofit one would need the firmware first.

 Any way if possible it would be much appreciated , but if not that's okay.
 BTW given the schematics it should be relatively straight forward to repair if needed.
Title: Re: Valhalla 2701c schematics + firmware V3
Post by: jasonbrent on February 14, 2018, 11:41:17 pm
@lowimpedance - I don't believe it does.. but I'll check it when it arrives. I don't currently have a programmer, but I can acquire one if it indeed has that option.
Title: Re: Valhalla 2701c schematics + firmware V3
Post by: jasonbrent on February 15, 2018, 09:45:54 pm
It looks like this doesn't have the 120mah option... but I need to crack it open. This is... very non-functional at the moment. It's producing 40volts out the rear in 20volt mode with the output on or off... and the front outputs are different yet again.

I guess this turns into My First Repair(tm). =)

*EDIT*: The traces for the banana plugs on the front were apparently desoldered at some point leaving only the rear banana jacks live. This unit has rack mounts on it, so it was likely a "safety" modification at some point in the past. I see a couple of date codes of 07 and 09, definitely doesn't have the 120mah option and the rom has a handwritten sticker that says "2701C-LNF" on it. I'm unsure if it's out of calibration because someone played with it, or if it is broken. The keys I ordered won't be here until Tuesday. In the interim, I'll start checking components on the board as best I can.

-j
Title: Re: Valhalla 2701c schematics + firmware V3
Post by: lowimpedance on February 15, 2018, 11:37:26 pm
If the current option is not installed there will be components missing at the front right hand side of the PCB. Post up a pic. of the inside of your unit to compare with others, to see if there are any significant revisions.
 As for the busted output , start your check at the Mosfet output string, (rear right hand side). one or more are likely S/C. Check TR11, 12 and D3 etc for starters.
Title: Re: Valhalla 2701c schematics + firmware V3
Post by: jasonbrent on February 15, 2018, 11:59:12 pm
Here's a few shots... whole board view and the unsoldered front panel.... and the special work around the transformer...

I'm about to check tr6-12 per the manual and then ic110/111, I think.

Repairing the front is easy enough, they look to be clean pulls.

(https://uploads.tapatalk-cdn.com/20180215/4a140741ea4746130a3d5f03f6408572.jpg)
(https://uploads.tapatalk-cdn.com/20180215/247455426c5ff3d9f8d7a84184a49af9.jpg)
(https://uploads.tapatalk-cdn.com/20180215/1b4a5eb9b9da8da25f630ffe159fbc03.jpg)

Title: Re: Valhalla 2701c schematics + firmware V3
Post by: lowimpedance on February 16, 2018, 12:18:26 am
 Sadly no current option, but whats going on with 'that' transformer bodge  :-//.
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.
Should show no IEEE I suspect. (proves that the comm's firmware is at least standard and just tests the installation of the connector to the interface PCB).
Of course only do this test after repairs.
PS I can post up any pictures of the inside of mine if you need any (if not already online).
Title: Re: Valhalla 2701c schematics + firmware V3
Post by: jasonbrent on February 16, 2018, 01:59:22 am
Bodges/kludges/questionables:

* External fuse is 1.5 amps installed, spec'd for 1.0 amp.
* Internal fuse (F1/100m marking on the board) is too large physically for the clips, so someone just shoved a fuse between the clamp posts bending them outwards to "make it fit".
* Whatever is going on with the transformer...
** The wiring around the transformer is much 'worse' than I see in other 27xx pictures. Most others have all of the wiring topside and soldering bottom with neat tiewraps. This one has no tiewraps and many of the wires are soldered from the bottom of the board instead of the top. .... I don't know if this is a "Feature" of the LNF option (which drops the 1200v secondary transformer...) or what.
* random components on the board have flux around the solder joints, but most joints are pristine; makes me think someone has repaired this before. majority of the flux is around the diodes.

I'm going to take my time with this and read/study... I'm honestly clueless with more gear than my skillset. So I'm going to try to grok what is going on around the board and see if I can identify anything that's been replaced vs. any documentation. Caps all look good... I'll open the bottom in a bit and see what's going on there.
Title: Re: Valhalla 2701c schematics + firmware V3
Post by: jasonbrent on February 16, 2018, 02:40:38 am
I think someone has pulled the mainboard out of this at some point completely and desoldered every wire that went to the board.... each wire joint has flux on it, is on the wrong side of the board, or is otherwise poor.

This should be fun.... I probably need to move this over to "repair" to not anger the Metrology gods. :)

(https://uploads.tapatalk-cdn.com/20180216/d0a811d4c3c34d1968938809a921571d.jpg)
(https://uploads.tapatalk-cdn.com/20180216/b388c8e9bed3b0caa77371ed1b0af9db.jpg)
(https://uploads.tapatalk-cdn.com/20180216/06c7a9d837401af1d4ac3b7ab4c95eee.jpg)


Title: Re: Valhalla 2701c schematics + firmware V3
Post by: jasonbrent on February 16, 2018, 03:17:56 am
The transformer input is interesting... what should be TR202 has the piece in the following picture in place... no markings on it other than the sinusoidal pattern on opposite corners and a +,- on the opposing corners.

+ goes to where D213 should be and feeds straight into the 16v 15000uF cap.

- goes to E3.

Is yours LNF? If so, mind sharing pictures of the board?

(https://uploads.tapatalk-cdn.com/20180216/6fd42a138c98cf57d0b1c5c04095638b.jpg)
Title: Re: Valhalla 2701c schematics + firmware V3
Post by: jasonbrent on February 16, 2018, 05:25:26 am
I'm thinking relay(s) at least... once powered on, output voltage is present.

* All of the precision resistors are in spec according to my keithley 2015... well, R41 confuses me, but I think that's due to the 0.0uF cap piggy backing on it.
* Operate/Standby does not change the output voltage (haven't checked schematic to see if a relay is connected, but none switches regardless.
* in 200mv range, it produces 0.100mV
* in 2v range, it produces 12V
* in 20v range, it produces 40V
* in 120V range, it produces 51V; interestingly enough, this is the only voltage range that I can impact with the front knobs. Turning the 10s place from 30 to 40 changes the output from 51 to 52 volts. In all other ranges, the front panel seems to have zero impact on the output voltage.

Relays flip when switching ranges; 1200V range is ignored because this has the LNF option.

I'm unsure how to test relays, especially on the board. Time to search....
Title: Re: Valhalla 2701c schematics + firmware V3
Post by: jasonbrent on February 16, 2018, 05:27:39 am
Sadly no current option, but whats going on with 'that' transformer bodge  :-//.
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.
Should show no IEEE I suspect. (proves that the comm's firmware is at least standard and just tests the installation of the connector to the interface PCB).
Of course only do this test after repairs.
PS I can post up any pictures of the inside of mine if you need any (if not already online).

Confirmed, it displays "no IEEE" with the board disconnected.
Title: Re: Valhalla 2701c schematics + firmware V3
Post by: jasonbrent on February 17, 2018, 04:56:05 am
At this point I'm stuck I think; in part in trying to decide if this board is in the middle of someone else's failed repair, or the way it's supposed to be, but ready for repair.

Rail voltages off of the transformers are all correct, both AC and DC. mosfet chain appears good for the outputs.

Q: Do ya'll hear a relay switch when you toggle between output and standby?

*EDIT*: I've manually tested the 8 relays on the board and they do seem to properly latch in both directions... at least one of them is weaker than the others on one latch.

There are components that used to be populated and have been cut off (pins still through the board, components just gone). I don't know if this is back to someone else's previous modifications, or part of the LNF (low noise floor) option.



Title: Re: Valhalla 2701c schematics + firmware V3
Post by: jasonbrent on February 18, 2018, 02:55:50 pm
Valhalla Scientific tells me that the LNF option was "discontinued years ago", even though it shows up on the 2701C's webpage; perhaps there is another "LC" variant that provides that low noise floor in current models.

This 2701C-LNF I have diverges from the schematics posted by a reasonable amount...including capacitors where resistors should be, and extra capacitors on the bottom of the board piggy backed on some of the high precision resistors. The high voltage caps, by comparison, have dotted line silkscreening on the front of the board to identify where the resistors on the bottom of the board would go.

So.. at my skill level I' having a hard time telling if someone tried to repair this, tried to modify it's functionality, or if this is a variation due to the Low Noise Floor option coupled with various repairs (there are very obvious signs of repairs that I would consider poor; flux that wasn't cleaned up, pieces of paper towel caught on the pins on the bottom of the board as if someone tried to wipe the board off, etc).

I've been scouring the internet for information on the LNF option, hopefully with associated pictures, but haven't had any luck yet.

Calibration keys arrive tomorrow, and while I don't think all of the wonkiness on this can be explained by calibration alone, I'm going to give that a shot as the next step. I've got a Hakko 808 on order so make it easier to pull and test these some of these thruhole components, and I've ordered a spare set of NoS ICs for everything except the microprocessor from fleabay... The next bit to order are some of the relays; I've got a couple that are questionable on their latching, and a couple of the latches seem to allow a small bit of conductance on what should be open circuits.

(.... and with the baby now crying, this thought process escapes my head... so hitting post and hoping it's cogent.)

*EDIT*: IC9 is unpopulated from sheet one, lower right. IC10 is populated. IC9 is a JFET just like IC8 and IC11; IC9->IC10 feeds into line 15 on IC108 which controls the relays. I'm unsure of the control flow here, but I can't grok why IC would be unpopulated. Currently trying to scavenge a LF356N (unlikely) before ordering a few. Either the -LNF option is primarily "remove a lot of parts" or someone decided to use this one as a donor unit or some-such. Meh.

-j
Title: Re: Valhalla 2701c schematics + firmware V3
Post by: lowimpedance on February 19, 2018, 12:02:00 am
 It looks very much like some one has done a butcher job in converting it to a "LNF" version by replacing both transformers and hacking out all the components related to the high voltage sections.
None of this looks like Valhalla mods, so who ever hacked into it presumably had access to the circuit details of the LNF version and Firmware too).
 One check to see if the ROM has the correct firmware is at start up the display will show 2701C40 which is the LNF identifier.
 Sorry I dont have any documentation on the LNF version, perhaps you could get that direct from Valhalla which may help you do a better job on this unit. 
I recall reading that the LNF version is limited to only +/- 40V out and uses toroid transformers !. (clearly not the bodged in ones in your unit). Also having a GPIB doubles the wideband noise spec. again.
 Given the correct details it should be possible to revise this unit properly. Or if your after more than 40V I would suggest moving it along as it may be too costly to repair it to its original high voltage version.
Considering the transformers will be Valhalla custom made ones and you will need those to start. The other componenets should be readily available and the firmware is attached here.
Title: Re: Valhalla 2701c schematics + firmware V3
Post by: jasonbrent on February 19, 2018, 12:08:30 am
It looks very much like some one has done a butcher job in converting it to a "LNF" version by replacing both transformers and hacking out all the components related to the high voltage sections.
None of this looks like Valhalla mods, so who ever hacked into it presumably had access to the circuit details of the LNF version and Firmware too).
 One check to see if the ROM has the correct firmware is at start up the display will show 2701C40 which is the LNF identifier.
 Sorry I dont have any documentation on the LNF version, perhaps you could get that direct from Valhalla which may help you do a better job on this unit. 
I recall reading that the LNF version is limited to only +/- 40V out and uses toroid transformers !. (clearly not the bodged in ones in your unit). Also having a GPIB doubles the wideband noise spec. again.
 Given the correct details it should be possible to revise this unit properly. Or if your after more than 40V I would suggest moving it along as it may be too costly to repair it to its original high voltage version.
Considering the transformers will be Valhalla custom made ones and you will need those to start. The other componenets should be readily available and the firmware is attached here.
Both the factory product sticker on the back and the bolt sequence suggest it is a "real" LNF. ... which yes, limits to 40v. :/

I'll spend a couple more days on it since I've spent a little on new ICs and calibration keys and then decide about using the 14 day return with this seller or selling it. Darn.

.... the serial number on the board makes me wonder if someone made a mistake at the factory, or what... it matches the exterior serial, however. I'd love to know the history of this unit.

I'm just imagining someone had an LNF and non-variant, LNF broke, they figured they'd adapt the other board, scratch in a new serial number, put it in the old LNF case and be good to go...

(https://uploads.tapatalk-cdn.com/20180219/aa8ae472670cddf6c11e4f3f4a41857c.jpg)(https://uploads.tapatalk-cdn.com/20180219/5699d101632efcacbb767ec7ad6179d8.jpg)
Title: Re: Valhalla 2701c schematics + firmware V3
Post by: lowimpedance on February 19, 2018, 02:25:51 am
 It would be nice to get the background to what happened to this unit, could be exactly as you suggested. Certainly had nothing to do with Valhalla.
Perhaps try to find another unit and keep this one for an interesting project  :D ... good luck.
Title: Re: Valhalla 2701c schematics + firmware V3
Post by: jasonbrent on February 19, 2018, 04:17:05 pm
Cal keys just arrived... and no go. Too far out of spec for calibration to work as I guessed. I've asked Valhalla for schematics on the LNF, will see if that yields fruit. Otherwise, I'm continuing to literally follow traces testing component by component while I wait on spares.

Another example is that IC110 and IC111 (if memory serves) calls for dual optocoupler 8 pin dips... mine has a single in one of the two (110 I believe).. which while that doesn't match the parts list, it DOES match the actual functionality. The electrical path through that particular socket only uses one optocoupler.

What's kind of interesting is the power rails generate 12volt and 40volt and that's basically what I'm getting on the outputs depending on range selected. Almost like the power rails are shorted straight through somehow. A frustrating learning experience. :-)

-j
Title: Re: Valhalla 2701c schematics + firmware V3
Post by: lowimpedance on February 19, 2018, 10:51:53 pm
 If Valhalla can supply the documentation for the LNF version that would make life so much easier and then this would be a very interesting project. A frustrating learning experience is good ! , it will stick in your mind and will be very useful for those 'other' frustrating learning occasions  :P.
Title: Re: Valhalla 2701c schematics + firmware V3
Post by: wictor on February 21, 2018, 06:33:53 am
Hi!

Does anyone have full schematics for older 2701 or 2701B? I cannot even find pictures of the boards of the oldest model.

Wictor
Title: Re: Valhalla 2701c schematics + firmware V3
Post by: jasonbrent on February 21, 2018, 04:42:31 pm
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/ (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.
Title: Re: Valhalla 2701c schematics + firmware V3
Post by: wictor on February 22, 2018, 06:04:35 am
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/ (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.

Yes, that seems to be best option right now.
Title: Re: Valhalla 2701c schematics + firmware V3
Post by: jasonbrent on February 27, 2018, 05:13:51 am
Update on my -LNF saga:

* Valhalla Scientific does not appear to have the -LNF schematics
* Their VP of engineering reached out to me in lieu of the schematics, but I've yet to hear back from him after my initial response. :/
* I've sourced and replaced every single relay ($$) and TR6-12 in the "output drive" section.
* I've sourced and replaced every socketed IC except the microprocessor, NOVRAM, and ROM.
* I've verified that the digital portion of the board appears to be doing the right thing at the signal level, things just aren't making it out the analogue end properly.

I've at least partially convinced myself that the components missing on the board are appropriate for the LNF variant after much tracing of the schematics. Otherwise, I think the -LNF is nothing more than a smaller transformer in place of the 1200V one, removal of the HV circuitry on the board, a rom check or different rom, and the addition of some 0.01uF filter caps across the banana plugs, and a few other spots on the board. Where I lose the convincing is around the analogue output side.... the manual describes HV analog function and I simply don't have the clue at the moment to translate it into how this should work otherwise.

Symptoms are still the same, unfortunately.

I've got replacement electrolytics en route as a hail mary.

-j
Title: Re: Valhalla 2701c schematics + firmware V3
Post by: precaud on March 01, 2018, 06:57:17 pm
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.
Title: Re: Valhalla 2701c schematics + firmware V3
Post by: lowimpedance on March 01, 2018, 11:37:08 pm
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  :P
Title: Re: Valhalla 2701c schematics + firmware V3
Post by: precaud on March 02, 2018, 03:47:21 am
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.

The manual I have says of the -LNF version that, if the GPIB option is installed, the noise improvement is reduced by 50% ....
Title: Re: Valhalla 2701c schematics + firmware V3
Post by: lowimpedance on March 02, 2018, 03:52:43 am
Same here in my manual !. As for the unit that Jason is working on its origin , as a LNF at least, is unclear as it certainly looks like some one had access to a proper LNF (as they have copied the firmware too) and have butchered a standard 2701c to become a LNF as you see in Jasons pictures above.
Title: Re: Valhalla 2701c schematics + firmware V3
Post by: jasonbrent on March 02, 2018, 04:12:35 am
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  :P

I'm beginning to think that the -LNF variants were hand adjusted, potentially by a very small number of people (1?); and those people/person isn't with them anymore, so the information is lost. Honestly, the only differences I see, other than removing a lot of the HV path is 7 capacitors. 4 across each of the pairs of terminals, and 3 in parallel with R42A/R42B/R41 -- 0.1uF 5% 100V caps that might be custom rolled (yellow, paper? unsure, can't take a picture at the moment).

Valhalla told me to check the output voltages and all of the rails match the schematic, except the HV rail between I and J on sheet 1 of the schematics.... that one simply isn't specified. I'm getting 376V potential across I/J which appears to simply match TR201's output between E20 and E21 (280V) plus TR202's E9-E10 (93V). I asked them to confirm what voltage should exist there and was told that they don't know --- they don't have an LNF to check. :)

As an aside, on sheet 1, TR6, part of the output drive, is listed as a TIP29A in the parts list; is a TIP31A a reasonable substitute there? I *THINK* it is based on the specs of each... but the TIP29A I pulled from the board seems to be fine according to this peak atlas DCA75.

I sat down with a "real" EE and the schematics a couple of days ago to look at the output drive section and at this point I'm wondering if the zener, D3, isn't misbehaving. In circuit, it is ~1.5MOhm in 1 direction, and ~55kOhm in the other... but in circuit could be lying to me.

Incidentally, I sent the same pictures from earlier in this thread to Valhalla asking if they could verify if that is what an LNF was supposed to look like, or if it was someone else's butcher job... They didn't appear to know, at least, they didn't answer that question, which was the only real question in my email. :)

Eventually this thing will work again....

-j
Title: Re: Valhalla 2701c schematics + firmware V3
Post by: Edwin G. Pettis on March 02, 2018, 05:03:37 am
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.
Title: Re: Valhalla 2701c schematics + firmware V3
Post by: jasonbrent on March 02, 2018, 05:08:13 am
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.

Hmmm, useful information. 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. http://www.sandia.gov/psl/_assets/documents/Electrical%20Lab%20Supported%20Equip (http://www.sandia.gov/psl/_assets/documents/Electrical%20Lab%20Supported%20Equip) 21May2015.pdf
Title: Re: Valhalla 2701c schematics + firmware V3
Post by: precaud on March 02, 2018, 02:21:05 pm
I have a couple 2701C's here in the repair pile, I'll look and see if either of them are LNF's.

Quote
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.

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  :)
Title: Re: Valhalla 2701c schematics + firmware V3
Post by: jasonbrent on March 02, 2018, 02:51:47 pm
I have a couple 2701C's here in the repair pile, I'll look and see if either of them are LNF's.

Quote
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.

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  :)
I had to go back and look, no it wasn't "solanotraders". I'll add that info to my mental filing cabinet though. :)
Title: Re: Valhalla 2701c schematics + firmware V3
Post by: precaud on March 03, 2018, 03:07:35 pm
Neither of my 2701C's are -LNF's...
Title: Re: Valhalla 2701c schematics + firmware V3
Post by: jasonbrent on March 03, 2018, 03:29:00 pm
Neither of my 2701C's are -LNF's...
Trade you one Rare^WVintage^Unique -LNF for a working 2701C in your pile? :-)

I guess I'll start up a thread in the Repair section and see if we can crowd source this. :)

Thank you for checking.

-j

Title: Re: Valhalla 2701c schematics + firmware V3
Post by: precaud on March 03, 2018, 03:46:23 pm
Trade you one Rare^WVintage^Unique -LNF for a working 2701C in your pile? :-)

Thanks for your kind offer  :)

Neither of mine are working, they've been patiently waiting in the repair pile for a couple years. I put numerous hours into troubleshooting each of them at some point with only partial success, and had to put them aside for a rainy day. Global Climate Change has given us far fewer such days, and so they have sat unattended to  ...   :)
Title: Re: Valhalla 2701c schematics + firmware V3
Post by: jasonbrent on March 10, 2018, 02:03:37 am
TL;DR: To test the analog circuitry, I took the digital out of the equation (I think). Still have the voltage potential where it shouldn't be. As best I can tell, with no signal out of IC5 pin 10 to TR12, the high voltage should go to 0va through D7 (I think..).

After setting this aside for a few days, I pulled pins 1,2,12,13 off of IC112 (feeds the 2 variable duty cycle square waves into the precision resistor chain and on to the chopper amp before hitting the mosfet output chain) temporarily to take the digital bits out of the equation. I still have the voltage potential that shouldn't be there. For anyone playing the home game (OPs post, "main board cct.pdf"), on the main PCB diagram, sheet 1, the voltage I see across the outputs when in standby mode is the same voltage I see across the pair of diodes D6/D5 and across C12.

On sheet 3, power supply, R223 (high voltage output, near "J" on the right) is a piece of wire on mine. R224 is in place, however. I don't quite understand how the windings on the low voltage transformer between E9/E10 that feed through "L" back to sheet 1 between R7 and the slow blow fuse F1 works. It basically looks like the T201 transformer sends to I/J on the output side, but T202 also helpfully gives another 120V as "L".

I think need to study input "L" at the very top of sheet 1 to understand the relationship between that, the F1 fuse, D1/D2/D5/D6/D8/D9... if I pull the fuse F1, I still get the same voltage potentials on the outputs... but I think that's an "input" protection fuse vs. output. I don't grok the current flow in this thing.  :-//.

While thing thing works exactly as it did when I received it despite all of my cutting/removing/replacing/testing, I'd be hard pressed to even put it up for sell as it'd just feel slimy.

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