Author Topic: Fluke 8800a repair  (Read 8554 times)

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Offline sycho123321

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Re: Fluke 8800a repair
« Reply #25 on: November 16, 2015, 03:48:00 am »
Thank you for those model numbers so I can replace the diode rectifier also the voltage across c11 is 11vac. Do you have any Idea what may be causing the 188888 blinking overload indacation on all the ranges? I have not had time yet to go through the rest trobleshooting in the manual yet.
-KD9A
 

Offline dacman

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Re: Fluke 8800a repair
« Reply #26 on: November 16, 2015, 03:54:19 am »
11 Vac across (C22)?  Seems like C22 may be shot.  Do you have an LCR meter?  Please check all the electrolytic capacitors.  Troubleshooting with bad power supplies is futile.
 

Offline sycho123321

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Re: Fluke 8800a repair
« Reply #27 on: November 16, 2015, 05:10:37 am »
No, I don' but someone I know has one, will have to borrow it from them.
-KD9A
 

Offline sycho123321

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Re: Fluke 8800a repair
« Reply #28 on: November 17, 2015, 04:29:33 am »
I got ahold of a lcr meter but it only measures up to 2000mfd while c11 is 4000mfd
-KD9A
 

Offline sycho123321

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Re: Fluke 8800a repair
« Reply #29 on: November 17, 2015, 04:59:39 am »
Hmm when  I measure across c11 in acv it shows 1vac max  :-// the rest of the caps look good too. Maybe not a psu failure?
-KD9A
 

Offline dacman

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Re: Fluke 8800a repair
« Reply #30 on: November 17, 2015, 11:51:18 pm »
What does it read if the input is shorted?  Are the four wire shorts attached?
 

Offline Shock

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Re: Fluke 8800a repair
« Reply #31 on: November 18, 2015, 01:03:01 am »
Did you end up swapping the U19 regulator? Under no load and ideal input they may look fine but the moment they get a little load be symptomatic.

Diode test the rectifier diodes/pins in both directions. C22 has some change mentioned in the beginning of the manual. If it's smoothing to 7V then 10V seems a little small and likely why the supply has problems, I'd pick up a 16V as well as a 10V for comparison. Check what they used though it might have been changed to some other odd value already, you will have to scope it for ripple anyway to be 100% sure.

Check those grounds are common and then measure that against the rail voltages e.g. +/-18 and -13.
Soldering/Rework: Pace ADS200, Pace MBT350
Multimeters: Fluke 87V, 117, 27/FM
Oscilloscopes: Rigol DS1054Z, Phillips PM3065
 

Offline sycho123321

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Re: Fluke 8800a repair
« Reply #32 on: November 19, 2015, 01:27:23 am »
What does it read if the input is shorted?  Are the four wire shorts attached?

Yes, there are  shorts on the banana jacks for the 4 wires, and it looks the same when shorted

Did you end up swapping the U19 regulator? Under no load and ideal input they may look fine but the moment they get a little load be symptomatic.

Diode test the rectifier diodes/pins in both directions. C22 has some change mentioned in the beginning of the manual. If it's smoothing to 7V then 10V seems a little small and likely why the supply has problems, I'd pick up a 16V as well as a 10V for comparison. Check what they used though it might have been changed to some other odd value already, you will have to scope it for ripple anyway to be 100% sure.

Check those grounds are common and then measure that against the rail voltages e.g. +/-18 and -13.

I did replace the u19 and the diode bridge is faulty, so right now I am powering the 5v rail w/ my bench supply. It is now showing overrange on all ranges so we know something is working. Also the grounds are not common. The ripple across c22 looks fine (I think the first time I measured it I did something wrong but it looks fine now)

Thanks guys!
-KD9A
 

Offline sycho123321

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Re: Fluke 8800a repair
« Reply #33 on: November 19, 2015, 02:31:16 am »
I just noticed also that the relay (k5) sometimes clicks sporadically when I change ranges.
-KD9A
 

Offline wiss

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Re: Fluke 8800a repair
« Reply #34 on: November 19, 2015, 07:24:33 am »
Do you have the inputs shorted?
The relay should click when go from 20V to 200V and vv.
 

Offline sycho123321

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Re: Fluke 8800a repair
« Reply #35 on: November 19, 2015, 11:42:29 pm »
The bannana jacks have the shorting bars going to the sense inputs, But I do not have the his and ground inputs shorted, and the relay clicks sporatically even when not swithching between those ranges.
-KD9A
 

Offline wiss

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Re: Fluke 8800a repair
« Reply #36 on: November 20, 2015, 09:57:23 am »
If it is in auto-range and inputs are open it will flip back and forth between 200V and 20V.
 

Offline halexa

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Re: Fluke 8800a repair
« Reply #37 on: November 20, 2015, 10:58:40 am »
Hi,

I have an 8800A donor unit if you are in need of spare parts.

Good luck with your repair.
 

Offline sycho123321

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Re: Fluke 8800a repair
« Reply #38 on: November 20, 2015, 10:45:49 pm »
Hi,

I have an 8800A donor unit if you are in need of spare parts.

Good luck with your repair.

That would be AWESOME!
I will pm you,
thank you
-KD9A
 

Offline wiss

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Re: Fluke 8800a repair
« Reply #39 on: November 21, 2015, 02:01:14 pm »
BTW, if it is autoranging, then the A/D probably works and the problem is upstream of that, i.e. something wrong with the display-circuit. 
 

Offline sycho123321

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Re: Fluke 8800a repair
« Reply #40 on: November 21, 2015, 10:06:17 pm »
It does not auto range I have been suspecting the adc, I think u11 is the adc right? Also when on auto range with the inputs open the relay does not click back and forth.
« Last Edit: November 21, 2015, 11:00:38 pm by sycho123321 »
-KD9A
 

Offline wiss

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Re: Fluke 8800a repair
« Reply #41 on: November 23, 2015, 12:59:58 pm »
U11 is the main controller, Q40, U4, U5 , U6 et.all are the integrator and comparator.
TP2 should have some kind of triangular waveform if the ADC is working.
 

Offline sycho123321

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Re: Fluke 8800a repair
« Reply #42 on: November 24, 2015, 12:23:05 am »
Yeah the ad/c is broken but I will ask halexa if he still has those components
-KD9A
 

Offline wiss

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Re: Fluke 8800a repair
« Reply #43 on: November 24, 2015, 11:09:34 am »
U11 come in 2 different versions, there is a jumper on the PCB you will have to change if you install "the other one".
 

Offline halexa

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Re: Fluke 8800a repair
« Reply #44 on: November 24, 2015, 11:39:44 am »
U11 come in 2 different versions, there is a jumper on the PCB you will have to change if you install "the other one".

How can you differ from the two versions?
« Last Edit: November 24, 2015, 12:14:39 pm by halexa »
 

Offline wiss

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Re: Fluke 8800a repair
« Reply #45 on: November 24, 2015, 12:29:13 pm »
It is set by W1, there is a note in the schematic about it.
 

Offline halexa

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Re: Fluke 8800a repair
« Reply #46 on: November 24, 2015, 08:18:24 pm »
Hi

Replacement parts U11, U4, U5, U6, Q40 and CR31 located and desolder ready for delivery to sycho123321.
 

Offline sycho123321

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Re: Fluke 8800a repair
« Reply #47 on: December 05, 2015, 10:08:10 pm »
Hey everyone!
I got the parts from helexa and soldered u4, u5, u6, q40, and cr31 in and cr31 did not fix the 5v rail so I am still powering that rail via a powersupply and it still showes overrange on all ranges, But since the u11 I got sent is the different version from mine I have to remove r121 and w1. Execpt that where the compnent overlay says w1 is there is a diode.
Any ideas?
-KD9A
 

Offline dacman

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Re: Fluke 8800a repair
« Reply #48 on: December 06, 2015, 01:33:28 am »
Trace U11 pin 10 and RN4 pin 5.
Also, if you have a diode checker (function) what do the four diodes of CR31 test at in the forward direction?
 

Offline sycho123321

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Re: Fluke 8800a repair
« Reply #49 on: December 06, 2015, 02:02:57 am »
RN4 pin 5 goes to the diode i was talking about. U11 pin 10 goes to r121. I do not have a diode tester.
Lukas
-KD9A
 


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