Author Topic: Fluke 8400A; No display.  (Read 21832 times)

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Offline Specmaster

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Re: Fluke 8400A; No display.
« Reply #125 on: December 04, 2017, 09:38:20 pm »
Well what do i do know? i think the 5s in the display are now mostly burned out.
Did you replace Q1 and Q2? these 2 in the main are responsible for regulating the 200V, but also bear in mind that I did point out that both the 200V and the 5V are both referenced to the 18V supply so if there was any transistor in the 18V supply that you didn't replace could also have contributed to the excessive output.

You can always pull the nixies out (and all the other cards) and see if the power supply can be pulled back into alignment with only itself in circuit. You may be able to source replacements for the nixie tubes and hope that 400v does not go anywhere elses on the circuits.
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Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #126 on: December 04, 2017, 09:45:49 pm »
Well what do i do know? i think the 5s in the display are now mostly burned out.
Did you replace Q1 and Q2? these 2 in the main are responsible for regulating the 200V, but also bear in mind that I did point out that both the 200V and the 5V are both referenced to the 18V supply so if there was any transistor in the 18V supply that you didn't replace could also have contributed to the excessive output.

You can always pull the nixies out (and all the other cards) and see if the power supply can be pulled back into alignment with only itself in circuit. You may be able to source replacements for the nixie tubes and hope that 400v does not go anywhere elses on the circuits.

I think this one is a write off without a parts unit, i got my eye on one with limited time left.

If i get a parts unit then this power supply is going into the junk bin,
A hopeless addict (and slave) to TEA and a firm believer that high frequency is little more than modern hoodoo.
 

Offline Specmaster

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Re: Fluke 8400A; No display.
« Reply #127 on: December 04, 2017, 09:49:27 pm »
Well what do i do know? i think the 5s in the display are now mostly burned out.
Did you replace Q1 and Q2? these 2 in the main are responsible for regulating the 200V, but also bear in mind that I did point out that both the 200V and the 5V are both referenced to the 18V supply so if there was any transistor in the 18V supply that you didn't replace could also have contributed to the excessive output.

You can always pull the nixies out (and all the other cards) and see if the power supply can be pulled back into alignment with only itself in circuit. You may be able to source replacements for the nixie tubes and hope that 400v does not go anywhere elses on the circuits.
I think this one is a write off without a parts unit, i got my eye on one with limited time left.

If i get a parts unit then this power supply is going into the junk bin,
Is this the one? https://www.ebay.co.uk/itm/FLUKE-8400A-DIGITAL-VOLTMETER/232439511136
Who let Murphy in?

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Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #128 on: December 04, 2017, 09:49:56 pm »
Yes, why?
A hopeless addict (and slave) to TEA and a firm believer that high frequency is little more than modern hoodoo.
 

Offline Specmaster

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Re: Fluke 8400A; No display.
« Reply #129 on: December 04, 2017, 09:51:19 pm »
Yes, why?
Its the only one I can see that why I thought it was, wack a offer on it now and that way you should prevent anyone else grabbing it.
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Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #130 on: December 04, 2017, 10:06:44 pm »
Yes, why?
Its the only one I can see that why I thought it was, wack a offer on it now and that way you should prevent anyone else grabbing it.

 :horse:  :horse:  :horse: Thats me when she gets home, i called it.
I am so dead if this blows up, i technically bought it with money i don't technically have yet. Piecing together earlier conversations to give myself a "yes".

A hopeless addict (and slave) to TEA and a firm believer that high frequency is little more than modern hoodoo.
 

Offline Specmaster

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Re: Fluke 8400A; No display.
« Reply #131 on: December 04, 2017, 10:12:08 pm »
Asking price or an offer accepted? When you get it, pull out the boards and run the power supply alone and see what you get and also check for any signs of burning on the PCB, you now know where to look for that don't you?
Who let Murphy in?

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Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #132 on: December 04, 2017, 10:13:39 pm »
The $28 was acceptable, and yes i now know what to look for. At least mostly. I still have no clue why it lost regulation, or even where the insane voltage came from.
A hopeless addict (and slave) to TEA and a firm believer that high frequency is little more than modern hoodoo.
 

Offline Specmaster

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Re: Fluke 8400A; No display.
« Reply #133 on: December 04, 2017, 10:15:06 pm »
The $28 was acceptable, and yes i now know what to look for. At least mostly. I still have no clue why it lost regulation, or even where the insane voltage came from.
I think that that could well be put down to the 2 transistors that you took a chance on don't you?
Who let Murphy in?

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Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #134 on: December 04, 2017, 10:19:57 pm »
The $28 was acceptable, and yes i now know what to look for. At least mostly. I still have no clue why it lost regulation, or even where the insane voltage came from.
I think that that could well be put down to the 2 transistors that you took a chance on don't you?

The only one i didn't replace is Q8, turned out i was smart and replaced all 2n3053's.

I fail to see how the voltage could become 10X what it was.
A hopeless addict (and slave) to TEA and a firm believer that high frequency is little more than modern hoodoo.
 

Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #135 on: December 05, 2017, 04:04:10 am »
Well the thought occurs to me in hindsight, after properly kicking myself for my mistake, is that i at least found the root of all problems, the power supply is completely FUBARepair

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Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #136 on: December 05, 2017, 04:31:39 am »
The furthest right digits on this meter are the two i tested and they both look fine so the rest of the display probably works.
One, not so small, problem, the board pretty much disintegrated when i touched it. So unless i get creative or have a new board made i am more or less screwed.

I'm probably just awful at de-soldering but it seems as it the circuit boards in this thing are particularly weak and prone to being destroyed
« Last Edit: December 05, 2017, 04:19:23 pm by neo »
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Offline Specmaster

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Re: Fluke 8400A; No display.
« Reply #137 on: December 05, 2017, 09:18:56 am »
The furthest right digits on this meter are the two i tested and they both look fine so the rest of the display probably works.
One, not so small, problem, the board pretty much disintegrated when i touched it. So unless i get creative or have a new board made i am more or less screwed.

I'm probably just awful at de-soldering but it seems as it the circuit boards in this thing are particularly weak and probe to being destroyed
Or of course have they been fried?
Who let Murphy in?

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Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #138 on: December 05, 2017, 04:21:17 pm »
The two nixies i got out say the others will be fine, though the problem is they won't go back in unless i get creative because of damage to the board.
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Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #139 on: December 05, 2017, 10:59:45 pm »
All transistors and capacitors replaced, its back into somewhat normal operation but now it's even more screwed up, just a different kind of screwed.

+200V = +  104V stable
 +18V = + 5.42V stable
 -18V = -31.42V stable
  +5V = + 4.35V stable


So, it's completely lost it's mind but hey at least it's stable!
It's down 2 digits that i took out to check how bad the damage was, turns out no damage but i cannot easily add them back. Due to damage, my fault  :palm:  :horse:.

EDIT: I also measured ripple,

+  5V, less than a quarter mV RMS
- 18V, 100mV RMS
+ 18V, less than a quarter mV RMS
+200V, 200mV RMS.
« Last Edit: December 05, 2017, 11:22:31 pm by neo »
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Offline Specmaster

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Re: Fluke 8400A; No display.
« Reply #140 on: December 05, 2017, 11:23:20 pm »
All transistors and capacitors replaced, its back into somewhat normal operation but now it's even more screwed up, just a different kind of screwed.

+200V = +104V  stable
 +18V = +5.42V stable
 -18V = -31.42V stable
  +5V = + 4.35V stable

So, it's completely lost it's mind but hey at least it's stable!
It's down 2 digits that i took out to check how bad the damage was, turns out no damage but i cannot easily add them back. Due to damage, my fault  :palm:  :horse:.
Hmm, so its getting a bit better, so the only other thing its now pointing directly at is UI and U2, the 2 voltage regulators on the 18V
rails, 1 on the +ve rail and the other on the -ve rail. If you add up the +5.42v and the -31.42v you actually get 36.84v and it states in the manual if you remember that the +200v and the +5v rails are referenced to the 18v rails.

Is this with the other cards in or out of circuit?
Who let Murphy in?

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Offline Specmaster

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Re: Fluke 8400A; No display.
« Reply #141 on: December 05, 2017, 11:24:59 pm »
Oh, I forgot, what's the temperatures like on the transistors now?
Who let Murphy in?

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Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #142 on: December 05, 2017, 11:25:42 pm »
With the power supply card completely removed from everything except the transformer.
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Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #143 on: December 05, 2017, 11:27:19 pm »
Transistors are cool, and at this point shouldn't the resistors that are way out of spec be of the slightest concern?
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Offline Specmaster

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Re: Fluke 8400A; No display.
« Reply #144 on: December 05, 2017, 11:27:55 pm »
Can you track the data on the regulators U1 and U2 if you can find their part number?
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Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #145 on: December 05, 2017, 11:32:56 pm »
LM301A, in this format they are rare and expensive. I'd have to buy 13 at once for $25.
« Last Edit: December 05, 2017, 11:34:38 pm by neo »
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Offline Specmaster

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Re: Fluke 8400A; No display.
« Reply #146 on: December 06, 2017, 12:15:54 am »
LM301A, in this format they are rare and expensive. I'd have to buy 13 at once for $25.
Its because the form factor has changed to DIP8 which are much cheaper but you'd have to come up with an interface to make it fit.

https://www.digikey.co.uk/products/en/integrated-circuits-ics/linear-amplifiers-instrumentation-op-amps-buffer-amps/687?k=lm301A

https://www.mouser.co.uk/Search/Refine.aspx?Keyword=LM301A

Both of these have the round ones in stock but are costly as you said.

With regard to the resistors I can't really see these making that much difference but if you have some there you could swap them out and just see if they do alter anything, even if you use a couple pots for the temporary trial.

Checking your list against the stated tolerances in your list the ones that fall outside of the tolerances are

spec    Val         Actual       Max value + tol
5%      5.6k       6.022k      5.88k
5%      220k      244.6k      231k
5%      5.6k       6.115k      5.88k
5%      51         57.12        53.55
5%      51         54.86        53.55

Can you find a spec sheet for the LM301A and see what the typical voltage on pin 3 is? On the +18v rail there is a connection from pin 3 to Power Supply Ref.

 

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Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #147 on: December 06, 2017, 12:22:04 am »
I have to admit when it comes to OP-amps i don't have the slightest idea what i am doing.
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Offline Specmaster

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Re: Fluke 8400A; No display.
« Reply #148 on: December 06, 2017, 12:26:24 am »
Found you another supplier for the LM301A, much much cheaper and in lots of 4 matched units here is the link.

https://www.ebay.co.uk/itm/4-Pcs-matched-National-Semiconductor-LM101AH-LM201AH-LM301AH-MIL-SPEC/322330297685

and

https://www.ebay.co.uk/itm/Integrated-Circuit-HP-1820-0223-LM301AH-GOLD-PIN-M1-HP-3/253216886787

Plus also looking at the pins on these, they would appear to arranged in 2 rows of 4, so it could be that a DIP8 package might be interchangeable with them and thus a fraction of the price as these seem to really cheap.
Who let Murphy in?

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Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #149 on: December 06, 2017, 12:29:57 am »
Mine use a circular foot print. DIP might could be mangled to fit if the pin arrangement is right
« Last Edit: December 06, 2017, 12:36:50 am by neo »
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