Author Topic: Fluke 8400A; No display.  (Read 21831 times)

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Offline Specmaster

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Re: Fluke 8400A; No display.
« Reply #50 on: November 29, 2017, 01:16:31 am »
Well with that LCR tester you have found, when that arrives you can test the transistor as already mentioned, you only have to remove it from the circuit and clip one of those leads to cach connection and the tester will tell which is the base, collector and emitter if the transistor is good or not. If it isn't then it will show up as a short circuit (resistor) or a diode and then you need to replace them, once you know what their state is . The same with caps, although with caps after a few years of service many people will replace them anyway as an insurance because after a few years it almost certain that they will fail at some point. That point will vary according to how often the equipment is switched and used and how hot the caps get. I always replace with 105C ones rather the lower 85C rated ones which will last for less time, especially in power supplies where the ambient temps are going to higher and will cause them to dry out quicker.
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Offline Specmaster

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Re: Fluke 8400A; No display.
« Reply #51 on: November 29, 2017, 01:27:39 am »
This is how the display will depict a transistor and as you can see it will show what each pin is and tell you if the transistor is npn or pnp and also the hfe as well as the forward voltage.

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Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #52 on: November 29, 2017, 07:35:53 am »
Ok I've reached another impasse, that is to say I've stumped myself.

The 200v line seems to be my chief concern with its odd behavior, of course the reason why the transistors getting hot is also pressing.
 Q3 is part of the +18V regulator, Q6 is part of the +5 and both are getting hot.

If there was a problem with either than i would expect to see it reflected as ripple or the like but instead it looks copacetic, their not even being dragged down.
The 200V railed seems to be fine at start up only to be dragged down lower and lower the hotter the transistors get.

 :rant:

Either ways i included schematics for those among us that actually understand transistor only power supplies, they make me go  :scared:


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Offline Specmaster

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Re: Fluke 8400A; No display.
« Reply #53 on: November 29, 2017, 09:26:11 am »
Alright, I fear that you're leaping ahead here before you've been able to confirm the very basics of the psu. Firstly you have the psu out of the unit and those caps must be checked and replaced if they are leaky, have a high ESR or of course a lower capacitance value than what they should be, these will have a direct bearing on the rest of the circuit and could be one of the reasons for the apparent overheating of Q3 and Q8.

The 5v supply is referenced from the +18v supply rail, so the 5v will be affected by any problem with +18v supply. Do you have a infra red thermometer or camera at all? If so I'd be inclined to pull the data sheets for those transistors and check their normal running temps against what your device tells you they are currently running at.

While I was waiting for the ESR tester to arrive, I'd also be dropping one leg on the resistors in the PSU and double checking the values are broadly in line with the schematic.
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Offline Specmaster

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Re: Fluke 8400A; No display.
« Reply #54 on: November 29, 2017, 11:42:13 am »
To show you how the LCR and transistor tester functions and is a great tester, it has helped me a lot with resolving problems with my various oscilloscopes I show you a couple of photos testing a suspect transistor from a vertical amplifier in a scope. I only just noticed that while I was using red, black and blue cables, with matching clips, somehow, the clips got soldered to the the wrong colour cable in the case of the blue and black ones as you will notice in the 2nd photo.

The first photo shows the suspect transistor which was supposed to be providing a +ve 5V in the middle of a PCB (not on the power supply as you would suspect, it was I think because it was only required for a couple of IC's) and it was actually chucking out 0.8V. After testing it and then replacing the transistor, it gave out the +ve 5V and it started to function correctly. I know that there are those that will not touch these chinese testers but I can honestly say so far I have nothing but praise for both of my testers they have been well worth their cost.

I also show a couple of photos of the battery one testing a resistor @ 15R +/- 10% and also my newly made resistor decade box maxed out which measures on my DMM's as being 9.998M, so the little lcr tester is again pretty close.







« Last Edit: November 29, 2017, 11:43:45 am by Specmaster »
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Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #55 on: November 29, 2017, 05:16:44 pm »
The replacement caps are on their way, I've said that already i think.

I don't have a digital thermometer but i do have a fairly accurate analog one, and checking the resistors i can do.
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Offline Specmaster

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Re: Fluke 8400A; No display.
« Reply #56 on: November 29, 2017, 05:26:29 pm »
The replacement caps are on their way, I've said that already i think.

I don't have a digital thermometer but i do have a fairly accurate analog one, and checking the resistors i can do.
Ok check the resistors,but you cannot use an analogue thermometer to check the transistors etc, you need a Infra red on or a infrared thermal camera.

https://www.ebay.co.uk/itm/142456227542 is like the one I use and will measure upto 250C
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Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #57 on: November 29, 2017, 05:28:35 pm »
It has a proper thermocouple, just an analog scale.
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Offline Specmaster

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Re: Fluke 8400A; No display.
« Reply #58 on: November 29, 2017, 05:36:05 pm »
It has a proper thermocouple, just an analog scale.
You can try it but I never find them any good, you need to be able to make contact with the item you want to measure and that means that if it is really hot you will get burned or if the item is alive, you will get a shock and also of course you just cannot get easy access to make contact but with this 9one as long as you can point the laser beam at the item / part you need to check then you're good to go, it just takes a seconds to find out an items temperature,
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Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #59 on: November 29, 2017, 08:06:34 pm »
I forgot to do a thermal probe before i de-soldered an end to each resistor.

One looks measures like a diode, except has resistor bands. White blue orange red. By my logical conclusion this is CR9.

The last resistor is a bit odd the code is green brown brown gold yellow which, besides being the only 5 band resistor, indicates 51.1 ohms except that it measures 538.9 and there is meant to be a 510 ohm resistor in circuit. By logical conclusion this resistor is meant to be that one.


SPEC   VAL       ACTUAL
1%      7.20K    7.202K
1%      4.02K    4.022K
5%      5.60K    6.022K
1%      9.53K    9.496K
5%       220K    244.6K
1%      40.2K    40.27K
5%      5.60K    6.115K
5%      68.0K    69.17K
1%       383K      382K
1%      40.2K    40.41K
1%      10.0K   10.054K
5%         51     57.12
1%      10.0K   10.023K
5%         51     54.86
« Last Edit: November 29, 2017, 08:08:52 pm by neo »
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Offline Specmaster

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Re: Fluke 8400A; No display.
« Reply #60 on: November 29, 2017, 08:57:07 pm »
None of those resistors are suspects, the CR9 is I think a Zener diode so the culprits on the PSU are going to be one or more of the following, transistors, capacitors (still my firm favorite) or it is just possible a bridge rectifier / bad solder joint/s.

Both the capacitors and the transistors will of course be tested by the chinese tester when you order it and it arrives.

The transistors that are getting hot, do they have heat sinks?
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Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #61 on: November 29, 2017, 08:58:43 pm »
None of those resistors are suspects, the CR9 is I think a Zener diode so the culprits on the PSU are going to be one or more of the following, transistors, capacitors (still my firm favorite) or it is just possible a bridge rectifier / bad solder joint/s.

Both the capacitors and the transistors will of course be tested by the chinese tester when you order it and it arrives.

The transistors that are getting hot, do they have heat sinks?

The reason their (almost) irreplaceable is that they are custom packages with integrated heatsink.

Should i replace the ones out of spec since i am in it anyways?
« Last Edit: November 29, 2017, 09:01:20 pm by neo »
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Offline Specmaster

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Re: Fluke 8400A; No display.
« Reply #62 on: November 29, 2017, 09:00:39 pm »
When they get hot, does the heatsink feel as hot or is it cooler?
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Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #63 on: November 29, 2017, 09:09:25 pm »
When they get hot, does the heatsink feel as hot or is it cooler?

Almost as hot but not quite.
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Offline Specmaster

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Re: Fluke 8400A; No display.
« Reply #64 on: November 29, 2017, 09:15:34 pm »
None of those resistors are suspects, the CR9 is I think a Zener diode so the culprits on the PSU are going to be one or more of the following, transistors, capacitors (still my firm favorite) or it is just possible a bridge rectifier / bad solder joint/s.

Both the capacitors and the transistors will of course be tested by the chinese tester when you order it and it arrives.

The transistors that are getting hot, do they have heat sinks?

The reason their (almost) irreplaceable is that they are custom packages with integrated heatsink.

Should i replace the ones out of spec since i am in it anyways?
No, they are not that far out that would cause any problems, the biggest one out of spec is the 220K R17 if you read the notes, may or may not be fitted as it is essentially in parallel with others to help trim out the +5v which is OK so I'd leave it.

The large transistor on the heatsink appears to have no screws to hold it on the heatsink, is that so?
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Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #65 on: November 29, 2017, 09:18:37 pm »
None of those resistors are suspects, the CR9 is I think a Zener diode so the culprits on the PSU are going to be one or more of the following, transistors, capacitors (still my firm favorite) or it is just possible a bridge rectifier / bad solder joint/s.

Both the capacitors and the transistors will of course be tested by the chinese tester when you order it and it arrives.

The transistors that are getting hot, do they have heat sinks?

The reason their (almost) irreplaceable is that they are custom packages with integrated heatsink.

Should i replace the ones out of spec since i am in it anyways?
No, they are not that far out that would cause any problems, the biggest one out of spec is the 220K R17 if you read the notes, may or may not be fitted as it is essentially in parallel with others to help trim out the +5v which is OK so I'd leave it.

The large transistor on the heatsink appears to have no screws to hold it on the heatsink, is that so?

Correct, though i think it may be held together somehow, not sure how.
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Offline Specmaster

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Re: Fluke 8400A; No display.
« Reply #66 on: November 29, 2017, 09:19:05 pm »
Where are the other transistors, I can only see 3 in the photo?
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Offline Specmaster

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Re: Fluke 8400A; No display.
« Reply #67 on: November 29, 2017, 09:20:33 pm »
None of those resistors are suspects, the CR9 is I think a Zener diode so the culprits on the PSU are going to be one or more of the following, transistors, capacitors (still my firm favorite) or it is just possible a bridge rectifier / bad solder joint/s.

Both the capacitors and the transistors will of course be tested by the chinese tester when you order it and it arrives.

The transistors that are getting hot, do they have heat sinks?
Are there holes in the heatsink at all?

The reason their (almost) irreplaceable is that they are custom packages with integrated heatsink.

Should i replace the ones out of spec since i am in it anyways?
No, they are not that far out that would cause any problems, the biggest one out of spec is the 220K R17 if you read the notes, may or may not be fitted as it is essentially in parallel with others to help trim out the +5v which is OK so I'd leave it.

The large transistor on the heatsink appears to have no screws to hold it on the heatsink, is that so?

Correct, though i think it may be held together somehow, not sure how.
Are there any holes in the heat sink?
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Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #68 on: November 29, 2017, 09:23:37 pm »
http://www.electronicsurplus.com/rca-40372-transistors-npn-cross-2n3054 That is Q6

The round brown things are transistors, the brown is their heatsink.

EDIT: to add that the only transistors on this board are either heat sinked or not in metal cans.
« Last Edit: November 29, 2017, 09:29:24 pm by neo »
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Offline Specmaster

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Re: Fluke 8400A; No display.
« Reply #69 on: November 29, 2017, 09:33:41 pm »
http://www.electronicsurplus.com/rca-40372-transistors-npn-cross-2n3054 That is Q6

The round brown things are transistors, the brown is their heatsink.

EDIT: to add that the only transistors on this board are either heat sinked or not in metal cans.
Oh, I see, I that they might be sockets  :-DD, they look as if they have been getting very hot and got discoloured then, do they get hot?

If you put a ohm meter across the heat sink and the 40372 body, are they connected electrically at all?
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Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #70 on: November 29, 2017, 09:40:56 pm »
Only one gets hot, that heatsink is lighter than the others, though they are meant to be that color i think.

Between the 40372 case and its heatsink is 0 ohms.
Also i stand corrected there is one transistor in a metal can that does not have a heatsink
« Last Edit: November 29, 2017, 09:52:37 pm by neo »
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Offline Specmaster

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Re: Fluke 8400A; No display.
« Reply #71 on: November 29, 2017, 09:57:45 pm »
Only one gets hot, that heatsink is lighter than the others, though they are meant to be that color i think.

Between the 40372 case and its heatsink is 0 ohms.
Also i stand corrected there is one transistor in a metal can that does not have a heatsink
OK, I'd be inclined to put some screws and nuts through the holes on the 40372 and heatsink then as you will see from the RCA manual, the hotter that gets, the greater derating factor has to be applied and as can be seen from the browning all around that area it has been really hot.
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Offline Specmaster

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Re: Fluke 8400A; No display.
« Reply #72 on: November 29, 2017, 10:01:35 pm »
Once the new caps arrive and are fitted, and if the transistors can be proved to be OK, then we are looking somewhere else for the problem.
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Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #73 on: November 29, 2017, 10:02:16 pm »
Only one gets hot, that heatsink is lighter than the others, though they are meant to be that color i think.

Between the 40372 case and its heatsink is 0 ohms.
Also i stand corrected there is one transistor in a metal can that does not have a heatsink
OK, I'd be inclined to put some screws and nuts through the holes on the 40372 and heatsink then as you will see from the RCA manual, the hotter that gets, the greater derating factor has to be applied and as can be seen from the browning all around that area it has been really hot.

I would have to drill through the pcb to add screws.
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Offline Specmaster

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Re: Fluke 8400A; No display.
« Reply #74 on: November 29, 2017, 10:07:28 pm »
In that case leave it, it was obviously designed to be like that.

We can't do anymore now until we can check / replace the caps and the transistors.
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