Author Topic: Fluke 8400A; No display.  (Read 21829 times)

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Offline Specmaster

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Re: Fluke 8400A; No display.
« Reply #150 on: December 06, 2017, 12:33:35 am »
Still be able use them I think, just reform the leads into a circular pattern?
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Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #151 on: December 06, 2017, 12:41:29 am »
Still be able use them I think, just reform the leads into a circular pattern?

Only if the pin arrangement is right, definitely worth checking
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Offline Specmaster

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Re: Fluke 8400A; No display.
« Reply #152 on: December 06, 2017, 12:53:17 am »
Of course, but an alternative could to get some DIP8 sockets and solder these in using resistor or capacitor tails to form extensions to the legs of the socket in such a fashion that they can be neatly formed into a circle and soldered in and then the new chips carely inserted into the sockets. Thats way even if the pins are in a different arrangement, the leads can be made long enough and if need be, insulated with heat shrink to get them in the correct order to match your pcb?

Like you I don't really understand much about OP Amps, but in this situation we don't need to because we are not designing this from scratch, simply trying to effect a repair and that is done, just as we are here in many cases by replacing bits until the smoking gun is found. This is also only necessary as there is no obvious culprit here, nothing has been fried to a crisp, nothing has spilled its guts out etc.
Who let Murphy in?

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Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #153 on: December 06, 2017, 12:57:43 am »
I could do that, but only if the leads wouldn't overlap.

For good measure i replaced the diodes and the new voltage values are
100V settling to 99, adverse reaction
5.4V in place of 18V
-31.75V in place of -18V
4.42 in place of 5V
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 #154 on: December 06, 2017, 01:01:08 am »
Good news, arrow has the op-amp for only 5 bucks in metal can, i assume LM301AH is acceptable to replace LM301A.
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 #155 on: December 06, 2017, 01:03:28 am »
The pins are in the same order and so will not cross over, I down loaded a datasheet from Digikey but the file size is too big to post here. but the dip8 pins etc are the same as the round package and so will be less expensive by far even with mounting sockets on stilts.
Who let Murphy in?

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Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #156 on: December 06, 2017, 01:09:07 am »
Here are the contenders,
DIP, 2 parts with sockets 5 bucks and a fair bit of a work.
TO , 2 parts 10 bucks, no excess work and qualifies my order for free overnight shipping.
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 #157 on: December 06, 2017, 01:13:54 am »
Here are the contenders,
DIP, 2 parts with sockets 5 bucks and a fair bit of a work.
TO , 2 parts 10 bucks, no excess work and qualifies my order for free overnight shipping.

Thats a call for you to make is that, now heres another, it seems that you have another 2 choices here, you could also use either LM101A or LM201A as there are effectively the same as the LM301A but have higher tolerances, pull down a datasheet from Digikey (its Texas Instruments one) its 24 pages long. Suddenly the world looks a bit brighter eh?
Who let Murphy in?

Brymen-Fluke-HP-Thurlby-Thander-Tek-Extech-Black Star-GW-Avo-Kyoritsu-Amprobe-ITT-Robin-TTi
 

Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #158 on: December 06, 2017, 02:06:26 am »
So if were going down the replace everything path then what do i do when the only thing left to replace is the board itself?
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 #159 on: December 06, 2017, 02:12:11 am »
The board is not the problem here, it cannot regulate the voltages can it? It could have a short though but that would not give you 400v. The other option you have is to wait till your other 8400A arrives and swap the power supply over from that one, assuming it's ok that is.
Who let Murphy in?

Brymen-Fluke-HP-Thurlby-Thander-Tek-Extech-Black Star-GW-Avo-Kyoritsu-Amprobe-ITT-Robin-TTi
 

Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #160 on: December 06, 2017, 02:22:51 am »
The board is not the problem here, it cannot regulate the voltages can it? It could have a short though but that would not give you 400v. The other option you have is to wait till your other 8400A arrives and swap the power supply over from that one, assuming it's ok that is.

Let me rephrase this to be entirely clear.

What do we do when there is nothing left to replace?

EDIT, To add: I think i found a removed the cause of the major problem when i replaced the last transistor.
« Last Edit: December 06, 2017, 02:39:27 am by neo »
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 #161 on: December 06, 2017, 03:15:07 am »
So you have replaced yet another transistor then, since the ones you did yesterday when you got 400V, yes?

Well lets hope so then if you think that was the cause, still be inclined to replace the OP amps incase they have been damaged by the strange and abnormal events that the PSU has been having.

To answer your question about what if, if everything is replaced and there is no improvement then, we shall need other peoples involvement on the remaining circuitry as that is way out of my comfort zone then.  What I would do if it was mine is to carefully and methodically lift a leg of each discrete component on each board and check it for value and ESR etc and if found to be OK resolder the leg and move on to the next part until I had covered every discrete part on the boards and then evaluate again.

Unless of course the service manual says otherwise, if it shows TP and voltages and trace patterns that should be present, then I'd check for them as stated in the manual. Its a long slow process of test and replace anything that is miles out of spec. I know of no other way unless I had a parts mule, in which case swapping out suspect cards one at a time is an option, but problem, is of course, you have no idea if the other cards are in working order til you try them.
Who let Murphy in?

Brymen-Fluke-HP-Thurlby-Thander-Tek-Extech-Black Star-GW-Avo-Kyoritsu-Amprobe-ITT-Robin-TTi
 

Offline Specmaster

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Re: Fluke 8400A; No display.
« Reply #162 on: December 06, 2017, 03:59:15 pm »
Here is a link to the other LCR meter I was referring to earlier, so I have one of these and also one of the ones that your ordered as well which I tend to use for a quick and dirty test although it is reasonably accurate especially when it's low cost taken into consideration. This one in the video however just blows it away and has results more in line with a professional piece of kit.

     https://youtu.be/rMFpWbLVTHo
Who let Murphy in?

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Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #163 on: December 10, 2017, 10:05:48 pm »
I got one working, pot is a bit scratchy so i'll contact clean it, now to the buttons, a keycap is missing, i can borrow that from the other one.  Some are sticky feeling and don't actuate well. As for the sticky ones, contact cleaner and perhaps a bit of sewing machine oil if their stubborn?

Regardless, it is almost dead on it, reads 1.216 as 1.213, thats as far as i tested it.
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 #164 on: December 10, 2017, 10:07:21 pm »
Great news :-+
Who let Murphy in?

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Offline Cubdriver

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Re: Fluke 8400A; No display.
« Reply #165 on: December 10, 2017, 10:49:42 pm »
Excellent news!!!!  Congrats, neo!

-Pat
If it jams, force it.  If it breaks, you needed a new one anyway...
 
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Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #166 on: December 11, 2017, 12:36:03 am »
I was able to install the DOU, RCU, and ohms converter, i'm still figuring out the wiring from the ohm's converter however. I have not tried the external dc reference board, the reason is that i don't have a external reference and it is a lot of work to install. Not a drop in part unless it came with an external reference card from the factory.

Also going over this thing again i notice alot of tantalums, after what they did to my 8800A i'm going to replace them all.

If tants from the 80's are scary, then what are tants from the 70's? Terrifying?  :-DD
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Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #167 on: December 11, 2017, 12:38:28 am »
Also i'm wondering if the lack of an AC RMS converter means it will measure true peak to peak voltage? it would be quite useful if it does.
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 #168 on: December 11, 2017, 12:44:31 am »
Also i'm wondering if the lack of an AC RMS converter means it will measure true peak to peak voltage? it would be quite useful if it does.
Not sure, it might just default to a pseudo RMS or average value? 
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Offline Cubdriver

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Re: Fluke 8400A; No display.
« Reply #169 on: December 11, 2017, 12:50:05 am »
Also i'm wondering if the lack of an AC RMS converter means it will measure true peak to peak voltage? it would be quite useful if it does.

My understanding is that RMS converters allow the meter to measure the RMS value of non-sinusoidal waveforms, and that AC meters that do not have them basically rectify the AC and measure the resultant DC average and apply a correction factor to get the AC RMS value.  The caveat with this method is that it 'assumes' that the AC being measured is sinusoidal - if it is not, the displayed voltage will not be the actual RMS value of the input wave.

If you only measure sine waves, then true RMS is not needed.  If you want to measure AC that's not a straight sine wave (such as the output of a triac type controller that gates the AC on at mid cycle), then  the  results will be inaccurate.

https://en.wikipedia.org/wiki/True_RMS_converter

-Pat
If it jams, force it.  If it breaks, you needed a new one anyway...
 


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