Nixie Tube Fluke 8100B DMM with Video

[tautech]

So, given my bad transistor. Do you more experienced folks think that that the bad transistor is the disease, or a symptom of some other problem?

2 bad transistors.

hFE 100-300.

http://download.njsemi.com/2N4946.pdf

Let's hope a faulty T102 is not the cause.

[Paul Moir]

(Currently hunting for a missing T102...)


EDIT:  Holey... Moley:  found missing T102.

[FlyingHacker]

So, given my bad transistor. Do you more experienced folks think that that the bad transistor is the disease, or a symptom of some other problem?

2 bad transistors.

hFE 100-300.

http://download.njsemi.com/2N4946.pdf

Let's hope a faulty T102 is not the cause.

Good point... I have ordered four.

[FlyingHacker]

(Currently hunting for a missing T102...)


EDIT:  Holey... Moley:  found missing T102.

You found a T102?  Where?

[tautech]

I kinda wish I had a battery pack for it............  But it would be cool to carry around this "portable" like the guy in the picture in the manual.

A real man would wear it on his wrist. 

[tautech]

(Currently hunting for a missing T102...)


EDIT:  Holey... Moley:  found missing T102.

You found a T102?  Where?

Paul's kindly measuring winding resistances for you.
 

[FlyingHacker]

(Currently hunting for a missing T102...)


EDIT:  Holey... Moley:  found missing T102.

You found a T102?  Where?

Paul's kindly measuring winding resistances for you.
 

I love you guys!

[Paul Moir]

Making me work for it eh?  Well I suppose it's penance for killing that poor thing all those years ago.  I'm recalling putting in one of the chips backwards....

OK from pin one, the one that goes to the electrolytic on the display side and powers up the nixies:

1-2 - 276.4 ohms
2-3 - 4.4 ohms
3-4 - 5.3 ohms
4-5 - infinity (No Connection)

Looks like an IC pattern pinout.  Pin 6 is across from pin 5:

6-7 - 8.6 ohms

8-9 - 4.1 ohms
9-10 - 4.2 ohms


EDIT:  Found T102 at the bottom of a box of mains transformers.  Had to dig out a few microwave ones, a VIC-20 PSU, and a bunch of other similair junk.  Box is a little mouldy but the transformer is OK.

[tautech]

And so we are all on the same page and for those finding this thread:

[FlyingHacker]

Hmmm. Thanks for the measurements!

  I am thinking I would have to desolder that t102 to get meaningful readings... Really would like to avoid that to avoid damaging it.

I am getting pretty similar readings in circuit:


MY VALUES ARE AFTER PAUL'S VALUES

1-2 - 276.4 ohms - 260.7 ohms
2-3 - 4.4 ohms -  4.6 ohms
3-4 - 5.3 ohms - 5.5 ohms
4-5 - infinity (No Connection) - ditto
6-7 - 8.6 ohms - 8.8 ohms
8-9 - 4.1 ohms - 4.4 ohms
9-10 - 4.2 ohms - 4.7 ohms

I think T102 looks good... Which is impressive since the last bloke that had this meter put a 1/2 amp fuse in F2 rather than the recommended 1/4 amp.

[Paul Moir]

Yeah, I wouldn't take it out if I were you.  That looks good enough.

I *think* a 2n4401 would be a fine replacement for those 2n4946, but if want to stay original fire me a PM with an address and I'll send some pulls and whatever else you might want a spare of. 

[tautech]

While waing for parts, it'd be a good idea to check E caps and devices that if failed across any of the rails might have overloaded Q4 & 5 and caused them to fail too.
That should keep you busy till new bits arrive. 

[FlyingHacker]

Yeah, I wouldn't take it out if I were you.  That looks good enough.

I *think* a 2n4401 would be a fine replacement for those 2n4946, but if want to stay original fire me a PM with an address and I'll send some pulls and whatever else you might want a spare of.

 I appreciate all your help. I may take you up on that offer. Let me figure out what I need first. I think I can get the 2N4946 from eBay. But there would be a number of things it might be nice to have spares of.

BTW, does your board have TWO small brown chicklet capacitors right next to Q4 and Q5 ? ( see my pic of the board, middle bottom). I only see one 22pf cap on the schematic, on the collector of Q4. I can't make out the values of either of them due to the angle. I don't know what serial number I have, as the little plaque on the front has come off (or was removed).

Somebody marked this as less that .5% error in 2002, which is a good sign.

[FlyingHacker]

While waing for parts, it'd be a good idea to check E caps and devices that if failed across any of the rails might have overloaded Q4 & 5 and caused them to fail too.
That should keep you busy till new bits arrive. 

Yeah, good idea. I think I have checked most of the electrolytics, but I will check the, again. Small ones can be checked accurately in circuit with my little "Transistor Tester" which doubles as a cheap ESR meter, and usually finds any bad larger caps.

[tautech]

I only see one 22pf cap on the schematic, on the collector of Q4. I can't make out the values of either of them due to the angle. I don't know what serial number I have, as the little plaque on the front has come off (or was removed).

See "Changes" on the schematic.
C68 (22pF) added SN 5050 and on.

[FlyingHacker]

I only see one 22pf cap on the schematic, on the collector of Q4. I can't make out the values of either of them due to the angle. I don't know what serial number I have, as the little plaque on the front has come off (or was removed).

See "Changes" on the schematic.
C68 (22pF) added SN 5050 and on.

I saw that note, but nothing saying what those two caps are. I can barely read "100" on both of them, and "1%". I don't think either one is 22pF. So maybe this is prior to serial 5050. Really annoying that the serial is missing... Hopefully nothing nefarious... Likely it just popped off, ass it was a glued on sticker on the front. Sadly that is where the Fluke logo was.

Thanks again for all your help (both of you).

[Paul Moir]

No, mine doesn't have those.  I think mine is earlier:  it never had a shield behind the nixie tubes and the top traces are gold plated.  I don't have the serial number anymore (unless it also chooses to reveal itself again this fateful night. )

Probably easiest just to circle what you want in a photo.

(Lousy cell phone picture follows).

https://picasaweb.google.com/lh/photo/AoBW6_-TLQ8tE3at4pQVuNMTjNZETYmyPJy0liipFm0?feat=directlink

[tautech]

I saw that note, but nothing saying what those two caps are. I can barely read "100" on both of them, and "1%". I don't think either one is 22pF.

Correct, they're as listed on the schematic.
C2 3.3nF or 3300pF or 332
C4 0.47uF or 470nF or 474

Guessing both are MLC and 100V, fairly normal values for this old stuff.
Even green caps should work.
For a sanity check.....measure them.

C68 (note 2) is only the revision after SN 5050 when this 22pF cap was added.
No other changes are listed for the primary side of T102.

As your unit has the C68 change and it seems you've found no other discrepencies, trust the schematic.

[FlyingHacker]

I saw that note, but nothing saying what those two caps are. I can barely read "100" on both of them, and "1%". I don't think either one is 22pF.

Correct, they're as listed on the schematic.
C2 3.3nF or 3300pF or 332
C4 0.47uF or 470nF or 474

Guessing both are MLC and 100V, fairly normal values for this old stuff.
Even green caps should work.
For a sanity check.....measure them.

C68 (note 2) is only the revision after SN 5050 when this 22pF cap was added.
No other changes are listed for the primary side of T102.

As your unit has the C68 change and it seems you've found no other discrepencies, trust the schematic.

Actually I don't think those two brown chicklets are C2 and C4. I believe C2 is the little round ceramic in the photo (came out reddish) between Q4 and the diode pair. Then C4 is the medium sized bright yellow-topped chicklet right above this (its left side next to the diode pair).

So I am not sure what the dark brown chicklets are. I would have to pull them to measure them. I will see what I can figure out. I don't think they are in the schematic I have.

The date codes on the two logic ICs seem to be 1972 (I think earlier in the year). Though they could have had stock on hand for a while.

[FlyingHacker]

Have some updates on the Fluke 8100B:

Got a replacement Q1 (RCA 40250). The Beta was much higher and correct. - INSTALLED

Got some replacement 2N4946s for Q4 and Q5. Beta much higher and correct. - INSTALLED

After these were installed I still had some issues. When I applied +15V to the +15V side of R5 (per the manual) I ended up blowing the replacement F2 1/4 amp fuse when using the mains input. I didn't want to waste a bunch of fuses, and would always rather work with lower voltages, so I connected my power supply up to the battery input jacks and disconnected the mains. I set the PS for 250mA and jumped the fuse instead.

At this stage I measured around -10V on the collector of Q1. Better, but not the -18V we should have. I noticed the power supply was current limiting. I also noticed that Q5 was getting warm again. I was doing short bursts so as not to kill another transistor. I noticed that I got only -2V on Q1 if I reconnected R5. So I began to think the issue was somewhere in the 15V supply.

I decided to pull out the electrolytics C5 and C7, as I had not been able to get a good test result on them in circuit.

C7 seemed OK. I replaced it anyway.

C5 tested on my "Transistor Tester" as a .63ohm resistor! I replaced C5... and...

[FlyingHacker]

BINGO! (as Dave would say).

[Vgkid]

Good job. The page jump killed me.
I see you have a dtack of Lambda psu's in the background.

[FlyingHacker]

So I should have replaced those electrolytics right away. It looks like the failed C5 was causing too much current to flow through Q5 and Q4, damaging them. This was not helped by the fact that the last guy had installed a 1/2 amp fuse.

I am still having an issue with the +15V supply, though. That photo was taken with me supplying +15V to R5 with an external power supply. When I reconnect R5 (with a jumper for now) I instead get ~+24V on the +15V side of R5. In other words, the +15V supply is pretty darned high.

I am going to ask for some help from those more knowledgeable than myself as to where to look first for that. I will definitely replace any other electrolytics. I am not sure if I got C8 yet or not. Unfortunately, only the transistors are silkscreened on the board. You have to trace it out to find the other parts (though caps are not hard to find).

I am pretty sure the -18V rail was close to -18V (will check). - CHECKED -18.4V

I am excited by this progress, and hope to have this guy up and running and "calibrated" soon.

[FlyingHacker]

Good job. The page jump killed me.
I see you have a dtack of Lambda psu's in the background.

Yeah that page jump was really lucky in a suspenseful type of way 

Yes, I like the old Lambda supplies. Rock solid. I have two of the triple LPT-7202-FMs and one 130V DC LHC-130-FM supply as well. Both of the 7202s required replacement of a one key capacitor per sub-unit. I got them for great bargains (~$35 USD) as not working. Now they are fully functional. On the top unit I have two of the 20V supplies in tracking mode for OpAmps. That Wun Hung Lo PSU under the high voltage Lambda on the right isn't even plugged in. I just don't use it. The Lambdas are pretty much bomb-proof in their construction.

[FlyingHacker]

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

The -18V "rail" is -18.4V when I am supplying R5 with a clean +15V. Should I be trying to get that closer to -18V? How? Maybe some tolerances have slipped. The specs call for up to -18.5V

Should T102 be humming/buzzing? I am guessing that is OK. Sounds like an old fluorescent light (one working properly, not a failing one).

Thanks!