Robert -
You evidently missed it in one of V's later posts... there is a completely isolated, dedicated Vref just for the test voltage. It just happens to be on the same PCB.
The one he was talking about replacing was this second Vref; I believe he fully intends to repair the circuit in the main Vref, as he has not damaged the temp compensating resistor for that ckt.
mnem
![Tweak :-/O](https://www.eevblog.com/forum/Smileys/default/smiliey_cal.gif.pagespeed.ce.yYMcAvxBJk.gif)
I don't think so. There apperars to be a single 6.2 V zenner biased from -12V and with two specified tempco resistors connected to it. One (at the top of tha diagram) feeds the main meter circuits and the other one a preset to give -4V to the test switch. The other Vref he refered to is in a second meter.
@vince, can you confirm if there is one or two zeners in each meter?
Yes you are right Rob. The schematic posted earlier is all there is to it. One Zener but two "taps"...
Sorry if I confused the Dwagon when I said there were two "references"... I meant two outputs which each serve a completely different purpose and don't interact, but of course as the schematic shows they stem from the same single 6.2V Zener.
Communication is a difficult skill...
![Confused :-//](https://www.eevblog.com/forum/Smileys/default/confused0024.gif.pagespeed.ce.5xOqKkq0Co.gif)
Anyway, just powered up the meter for the first time today... bad idea : doesn't work any more !
![Sad :(](https://www.eevblog.com/forum/Smileys/default/xsad.gif.pagespeed.ic.L3FGyzQrjB.png)
It looks like all Nixie tubes are counting relentlessly, they never stop... obviously this is controlled by the comparator board which generates the "gate" signal for the counting. So I swapped that board and ... works again. Better yet : the 50V and 500V ranges which were last night as I said, completely out of whack, now appear to be reasonable ?! How can that be.... how is this board concerned with ranges... it's the attenuator board that's supposed to handle that...
This meter is confusing me
![Confused :-//](https://www.eevblog.com/forum/Smileys/default/confused0024.gif.pagespeed.ce.5xOqKkq0Co.gif)
The manual is not good enough to help me as much as it could.. there is no detailed block diagram, not enough detail in the theory of operation chapter, and the schematic is a bit messy, hard to see the structure inside that comparator board, or even the attenuator board either really. None of the signals / wires are labelled, other than the power supplies. It's just a bunch of discrete components thrown on a piece of paper with spaghetti wiring everywhere. It's hard to understand in detail what signal is what, where it goes and how the circuitry is organized
![Confused :-//](https://www.eevblog.com/forum/Smileys/default/confused0024.gif.pagespeed.ce.5xOqKkq0Co.gif)
There is n,o board layout either, and on the board none of the components are identified ! Good luck Vince !
But clearly I need to concentrate on the comparator board, the heart of the instrument. Need to try to make sense of the schematic and try probing around.
What annoys me is that the polarity Nixie also stopped working on the GOOD board... weird. Did I do something wrong when swapping these boards... did I short or damage something...
![Undecided :-\](https://www.eevblog.com/forum/Smileys/default/undecided.gif.pagespeed.ce.cCZ6w-jWpR.gif)
Lots of work left to do on this meter for sure !!!
![](https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/?action=dlattach;attach=1457545;image)