Nixie Tube Fluke 8100B DMM with Video

[Paul Moir]

Congrats! 
My old one buzzed like that.  I'm sure it's normal.

[FlyingHacker]

Congrats! 
My old one buzzed like that.  I'm sure it's normal.

Thanks for the reassurance on the humming.

Any thoughts on how to get the +15V working within spec?

Thanks!

[Paul Moir]

No.  I guess it's time to power up Frankenstein?

EDIT:  Damn, I took my soldering iron to work.  Will have to wait until tomorrow.

[FlyingHacker]

No.  I guess it's time to power up Frankenstein?

EDIT:  Damn, I took my soldering iron to work.  Will have to wait until tomorrow.

Frankenstein? Your 8100?

[Paul Moir]

What's left of it.  It has been dead for some time now.

But the PSU is intact, so I'll try powering it up so I can get some references for you.  First though I'll have to reattach T102 and the transistors I've pulled.

[FlyingHacker]

What's left of it.  It has been dead for some time now.

But the PSU is intact, so I'll try powering it up so I can get some references for you.  First though I'll have to reattach T102 and the transistors I've pulled.

Ah. Thank you so much for all your help!

Your power supply was putting out voltages within spec?

[tautech]

So, still trying to figure out why the +15V output is around +24V.

You still have some work to do.
Reading the manual at section 3-53 and 4-39 and table 4-5 voltage at C5 pos should be +16.5- 17.5V.
C7 pos after the +15V regulator shold be +15.
There is a bit going on with this PSU and some study is needed.

Problem is +15 regulator gets its reference from the zener portion of Q11, a bipolar/zener reference that does not have a device # in the BOM. I hope it's not unobtainium.
Have you checked Q6?

Should T102 be humming/buzzing?

Manual specs it's operating frequency at only ~250Hz. 
Yep, it's likely to hum.

[FlyingHacker]

So, still trying to figure out why the +15V output is around +24V.

You still have some work to do.
Reading the manual at section 3-53 and 4-39 and table 4-5 voltage at C5 pos should be +16.5- 17.5V.
C7 pos after the +15V regulator shold be +15.
There is a bit going on with this PSU and some study is needed.

Problem is +15 regulator gets its reference from the zener portion of Q11, a bipolar/zener reference that does not have a device # in the BOM. I hope it's not unobtainium.
Have you checked Q6?

Checking Q6 was next, after checking all the resistor values in that part of the circuit.

That Q11 is a little metal can which may even include the Zener in it, though I have to check on that. It is supposedly factory matched to R15 and R22, presumably to set the voltage based on the particular Zener breakdown voltage. I am guessing Zeners of the day had far worse tolerances.

If Paul can get some reading off his power supply then perhaps I could tune that by hand if I had to.

As a LAST resort I could always add a 7815 

[FlyingHacker]

So Q6 is bad... Measures as a 63 ohm resistor on the Transistor Tester, and the Micronta will not even read an hFE.

Q6 is a 2N3906.

I don't have any of those on hand, though I do have some on order (slow ship though). I do have a 2N2907 though. Do you think this would be a suitable replacement? Or should I really wait for the right part, which is coming from China?

Boy, Tautech, you are 2 for 2 at guessing failed parts. I get the feeling you have done this a few times 

[tautech]

Boy, Tautech, you are 2 for 2 at guessing failed parts. I get the feeling you have done this a few times 

No guess, Q6 is a linear regulator pass transistor and it was not doing it's job. It could be either conducting or open, in this case failed short. Remember the likes of pass transistors are doing some work, much like output stage transistors and they ocasionally fail, but why? Overcurrent?

So Q6 is bad... Measures as a 63 ohm resistor on the Transistor Tester, and the Micronta will not even read an hFE.

Q6 is a 2N3906.

I don't have any of those on hand, though I do have some on order (slow ship though). I do have a 2N2907 though. Do you think this would be a suitable replacement? Or should I really wait for the right part, which is coming from China?

A 2N2907 should do to get her running although there's enough differences in datasheet specs to not leave it there. Watch the pinouts, they are very different.

[FlyingHacker]

Boy, Tautech, you are 2 for 2 at guessing failed parts. I get the feeling you have done this a few times 

No guess, Q6 is a linear regulator pass transistor and it was not doing it's job. It could be either conducting or open, in this case failed short. Remember the likes of pass transistors are doing some work, much like output stage transistors and they ocasionally fail, but why? Overcurrent?

Ok. I understand the basics of that. Not sure why the resulting voltage was more like +24V. I guess it was just taking the input voltage.

I assume it was over current that caused the failure. I think C7 may have been bad. I should have taken notes. I had replaced it.

So Q6 is bad... Measures as a 63 ohm resistor on the Transistor Tester, and the Micronta will not even read an hFE.

Q6 is a 2N3906.

I don't have any of those on hand, though I do have some on order (slow ship though). I do have a 2N2907 though. Do you think this would be a suitable replacement? Or should I really wait for the right part, which is coming from China?

A 2N2907 should do to get her running although there's enough differences in datasheet specs to not leave it there. Watch the pinouts, they are very different.

I installed the 2N907 (which had a measured beta of ~234 even though AllTransistors said it was 35 minimum). And now everything is working! 

So Paul, keep that soldering iron cold for the moment.

I am still powering it off my bench supply hooked to the battery terminals. Doing this just to watch current flow, and not waste fuses. It is drawing about 110 mA, if I recall.

Voltage measurements to follow, but everything is within spec! None of the transistors are warm, either.

Thank you guys for all your help. Paul, I may consider some of your parts as spares if you are game.

Pics to follow too. I think I shall wait for the proper transistor to really calibrate this guy, but it is pretty close as is.

[FlyingHacker]

Here's where we are with the voltage test points:

-18V = -18.29
+15V = 14.81
+17V = 16.82
+7V. = 7.00
+5V = 4.94
+200V = 191.8

The voltage remain rock solid if I vary the "battery" voltage up and down 8V or so.

[FlyingHacker]

Here is a video follow up with some Nixie tube porn, and an extremely cursory look at the problem and solution.


https://youtu.be/bOKkrFakrys

To quote Dave, "If you like it please give it a big thumbs up."

[FlyingHacker]

Following that video I keep her running for a couple of hours. I did a little rough calibration of the kilo ohms, which was a tiny bit off.

I periodically rechecked all the voltages, and kept an eye on the current. Everything was very steady!

I think I shall wait for the actual 2N3906 to put back in for Q6, which I substituted with a 2N2907. After I get that in and stable then I will try it out on mains. I am not for seeing any issue running it off the mains, just don't want to risk more fuses until I know everything is stable.

The DCV is surprising accurate. It was matching my Fluke 8810A, except when negative, in which case it was off in the last two digits. I believe there is a setting for that, but have not tried yet.

Thanks again for all your help!

[Paul Moir]

Hey, I had Q6 way back in the first post in the "Transistor Testing" thread!  Must have been ESP because it certainly wasn't skill. 

Of course you're welcome to spare parts.  Just let me know what you want. 
(I have to build up some good karma before the 8120A arrives.)

[FlyingHacker]

Hey, I had Q6 way back in the first post in the "Transistor Testing" thread!  Must have been ESP because it certainly wasn't skill. 

Of course you're welcome to spare parts.  Just let me know what you want. 
(I have to build up some good karma before the 8120A arrives.)

I will PM you about the parts.

Is the 8120A supposedly in working condition? Or do you need to troubleshoot it?

[Paul Moir]

Sold "As is" due to inability to test.  Shown powered up with some potentially correct and apparently changing digits on the AC range with the inputs floating.  Seller sells a lot of old lab gear and it seems to be all "as is". 

Maybe good, maybe bad.

[Paul Moir]

Oh, it arrived!

Mostly working OK from my brief checks.  A little wonky at startup and displaying signs that it's range switches need to be cleaned.  The only real fault I've found so far is that the DC autopolarity function does not seem to work - I can only read negative voltages.  The +- circuit seems OK though.  Will start a thread on it.

Looks like about a '72 given the date codes and the "Inventoried 1972" sticker.  Someone replaced the 74141 at some point.   Oh, and the Sandia Laboratories sticker is staying. 

[FlyingHacker]

Oh, it arrived!

Mostly working OK from my brief checks.  A little wonky at startup and displaying signs that it's range switches need to be cleaned.  The only real fault I've found so far is that the DC autopolarity function does not seem to work - I can only read negative voltages.  The +- circuit seems OK though.  Will start a thread on it.

Looks like about a '72 given the date codes and the "Inventoried 1972" sticker.  Someone replaced the 74141 at some point.   Oh, and the Sandia Laboratories sticker is staying. 

Awesome! I would definitely leave the Sandia Labs sticker! Like some of my other items with McDonnell Douglas stickers.

[Paul Moir]

Well, just cleaning the damn switches seems to have it working perfectly now.  I'll post a teardown once I get some time since repair consisted of cleaning and replacing the current range fuse.
Though I don't have any real standards, it matches my most trusted DMM and a few precision resistors I have around.  I'm not even tempted to touch the calibration.
The current shunt is neat.  It's a board that goes on over the switch shafts, and picks up the range switches with little levers.

[crispy_tofu]

BINGO! (as Dave would say).

Winner winner chicken dinner!
Congratulations on the repair! 

[Chuy]

Hello.
What was wrong with the Lambda before you replaced the capacitor?

I just bought one and have this problem, I just post a new post here at eevblog:

Hello everyone.
I just got this used Lambda LPT-7202 but it doesn't deliver enough current on all 3 outputs.
I calibrated all 3 voltages and was able to bring the voltage to the maximum value but on the Current calibration, I was short 1 amp even though I rotated the R102. R202 and R302 to the maximum.
The problem is when I connect a load even a small motor or light bulb, the voltage drops down to 3 volts and the motor bearly rotates or the lights barely light up, this happens on all 3 outputs.
I also put a jumper to the V+ and V- to adjust the current to the maximum and it does the same thing.

For example;
I turn on the power supply without load and adjust the voltage to 10 volts with the maximum current then I connect a car light bulb (12 v) immediately the voltage drops to 3 volts and the light bulb bearly lights up.

Photo attached.

I can turn the voltage knob to a higher voltage but it doesn't go up, stays on at 3 volts.

Happens on all 3 outputs.

Any suggestions/advice on what to do?