Author Topic: Fluke 8400A; No display.  (Read 21828 times)

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Offline Specmaster

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Re: Fluke 8400A; No display.
« Reply #100 on: November 30, 2017, 10:43:12 am »
Ok, I've had a quick look through the manual and all the voltage rails are interlinked with each other and the main one that everything references is the 18v so that has to be 100% healthy before the others can function correctly so if the regulators and the transistors are readily available I think I'd be inclined to replace them all without exception and also the caps on A1 card, the PSU. The diodes all checked out as OK and the resistors so then you will have effectively, a refurbished PSU card.

Next I'd run the meter with the bare minimum card set up, which as going to be the following cards installed, A1, A2, A8, A9, A10, A11, A12 and A13 and see what happens both to the voltage rails, ripple and display, then I'd follow the chart on pages 4.16 and 4.17.

Section 6 deals with the option cards and suggests items to check if checks run on them fail so it looks to be a good manual, just need to be patient and read it through and follow logical steps before moving on to new things.
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Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #101 on: November 30, 2017, 10:53:23 am »
What leads you to believe Q1 and Q2 needs replaced? Their not getting hot in themselves, maybe warm.

Also i apologize if i seem to drag my feet on spending money, but the transistors, while available, are relatively expensive.

EDIT: A full transistor rework would only cost about 20 bucks so if it is necessary it's necessary

In that plan of just replace everything do i also replace the non heat sinked 2n3053?

Q7 is 2 cents so i might as well, the 2n3053s are cheapest in a 4 pack.

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=360901874911
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=263311413215
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=172991048457
« Last Edit: November 30, 2017, 11:34:38 am by neo »
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Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #102 on: November 30, 2017, 11:19:54 am »
I found one thing odd, Q5 is listed as 2n4037, but is marked as 2n4890 and is the only motorola part i have seen.
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Offline Specmaster

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Re: Fluke 8400A; No display.
« Reply #103 on: November 30, 2017, 01:09:34 pm »
What leads you to believe Q1 and Q2 needs replaced? Their not getting hot in themselves, maybe warm.

Also i apologize if i seem to drag my feet on spending money, but the transistors, while available, are relatively expensive.

EDIT: A full transistor rework would only cost about 20 bucks so if it is necessary it's necessary

In that plan of just replace everything do i also replace the non heat sinked 2n3053?

Q7 is 2 cents so i might as well, the 2n3053s are cheapest in a 4 pack.

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=360901874911
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=263311413215
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=172991048457
The reason why I said that is the fact that many since you have had it, have been getting rather hot to say the least, transistors are not meant to get hot, warm yes if they are power ones like the big TO66 one with its heatsink, the others with their heatsinks warm only and the plastic one not at all. What we do not know is just long they have been getting hot before you acquired the meter or what that has done to their characteristics. You do know that Q1 and Q2 are producing some odd artifacts and a square wave on the noise floor.

If you read the manual, in the power supply section it describes how it all works together and the 18v section is linked to both the 200v and the 5v, both of which seem to be having issues, 200v changes and even drops to 75v but the information in the manual states that at TP1 you should be getting 200v +/- 5v, so anywhere between 192-205v is acceptable, 80v etc is not.

Q6 is on the 5v rail and getting extremely hot at 70C and this is once again linked and referenced to the 18v section and this section is common to both of the sections that you currently know for certain have issues, the 18v itself might also have issues but not exhibiting it at the moment.

We know that the resistors and diodes, are OK so if the other suspect parts are replaced then you will know for sure that your starting off with a rock solid platform that you can then outwards from card by card until you have it up and running again.

If you don't want to spend money at the moment thats up to you, but you currently have a whole box full of unknown cards and a motherboard, all of which all rely on a good healthy source of power to work so that why I feel that you need be certain in your mind that that it is good and fit for purpose.
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Offline Specmaster

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Re: Fluke 8400A; No display.
« Reply #104 on: November 30, 2017, 01:26:31 pm »
I found one thing odd, Q5 is listed as 2n4037, but is marked as 2n4890 and is the only motorola part i have seen.
Thats not unusual as most major manufacturers will have their own part numbers and references printed on the parts to make sure that the parts for it were purchased from them should they ever become required. It probably means that someone has trouble with the PSU before you and they discovered the original part was in fact a 2N4890 or that was an equivalent transistor transistor to the 2N4037.

In fact that is what appears to be the case, I just googled the 2N4890 and here is the result http://www.datasheets360.com/part/detail/2n4890/6089189740660391419/?alternatePartManufacturerId=0 and you will see that it is a functional equivelent to the original 2N4037 and so are 2N3503, 2N3576 and also 2N4028, and that 2N4037 is now obsolute and discontinued.

Remember, Google is your friend and solve many mysteries for you.
 
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Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #105 on: November 30, 2017, 07:17:15 pm »
I will admit google can be useful, i just sometimes miss something.

The non heat sinked parts are not getting warm, Q1 and Q5 are not getting particularly warm either, Q2 gets warm and Q3 gets hot. But you do have a point about giving myself one reliable card so i'll definitely consider it.
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Offline Specmaster

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Re: Fluke 8400A; No display.
« Reply #106 on: November 30, 2017, 07:45:32 pm »
At the end of the day its your money, you spend it how you want to, but if I was attempting to do what you're doing, thats what I'd do and then I have a known position of strength to work from. I don't know how much you paid for the 8400A but whatever it was it could become an expensive boat anchor and the first basic rule is to work from the power supply outwards and you do know that its not anywhere near 100%.

But for now, I'd read the part of the manual through where it describes the way the whole system works to gain an idea of what to do next.
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Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #107 on: November 30, 2017, 07:56:33 pm »
My collection of vintage parts finally paid off i found i had a set of 4 2n3053s from '72.

You said 2n3053 can be used for the 2n4037?
« Last Edit: November 30, 2017, 07:59:07 pm by neo »
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Offline Specmaster

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Re: Fluke 8400A; No display.
« Reply #108 on: November 30, 2017, 08:06:01 pm »
My collection of vintage parts finally paid off i found i had a set of 4 2n3053s from '72.

You said 2n3053 can be used for the 2n4037?
No No, 2N3503 I said, check on the link I sent you.
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Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #109 on: November 30, 2017, 08:09:00 pm »
Thank you for correcting me, i get numbers confused sometimes.
« Last Edit: November 30, 2017, 08:18:17 pm by neo »
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Offline Specmaster

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Re: Fluke 8400A; No display.
« Reply #110 on: November 30, 2017, 08:26:09 pm »
Thank you for correcting me, i get numbers confused sometimes.
Best be very careful with that then, 1 digit out can get you a totally different animal altogether in this game.
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Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #111 on: November 30, 2017, 08:47:03 pm »
Thank you for correcting me, i get numbers confused sometimes.
Best be very careful with that then, 1 digit out can get you a totally different animal altogether in this game.

I tend to double check myself, though thank you for your warning.
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Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #112 on: November 30, 2017, 09:22:37 pm »
The original 2n4037 is available new for 2 bucks.

I got a big box of capacitors coming for this and for several things in my repair que, and i probably will have the transistors coming soon.

At the end of the day its your money, you spend it how you want to.

 :-DD Don't say that to the wallet (as i jokingly refer to her), she might disagree.
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Offline Specmaster

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Re: Fluke 8400A; No display.
« Reply #113 on: November 30, 2017, 09:31:33 pm »
The original 2n4037 is available new for 2 bucks.

I got a big box of capacitors coming for this and for several things in my repair que, and i probably will have the transistors coming soon.

At the end of the day its your money, you spend it how you want to.

 :-DD Don't say that to the wallet (as i jokingly refer to her), she might disagree.
Great news, another term for the wallet could be "Her indoors"  :-DD
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Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #114 on: December 01, 2017, 02:51:11 am »
The original 2n4037 is available new for 2 bucks.

I got a big box of capacitors coming for this and for several things in my repair que, and i probably will have the transistors coming soon.

At the end of the day its your money, you spend it how you want to.

 :-DD Don't say that to the wallet (as i jokingly refer to her), she might disagree.
Great news, another term for the wallet could be "Her indoors"  :-DD

I may be a bit dim but i don't get it.

Regardless i have all the replacement transistors coming, as well as diodes just to be extra sure.

Diodes are all going to be vishay 1n4005, 1 2n4037 transistor, 2 RCA 40372 and a complete set of electrolytics for the unit.

I may not get them all at once, i ordered all of it today because of it being the end of the month. Most of the capacitors are coming from arrow, some from digikey with the diodes and lone transistor. The 40372s are coming off ebay as is the transistor tester so it may be some time.

When i'm done the only originals on this board will be the resistors and two op-amps.
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Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #115 on: December 01, 2017, 02:54:51 am »
In case your wondering why i bought two 40372s there is one on the power supply and then there is one in the A8 and A9 set that, if all these are going and or are suspect, is the next likely suspect.
« Last Edit: December 01, 2017, 03:37:29 am by neo »
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Offline Specmaster

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Re: Fluke 8400A; No display.
« Reply #116 on: December 01, 2017, 09:39:02 am »
The original 2n4037 is available new for 2 bucks.

I got a big box of capacitors coming for this and for several things in my repair que, and i probably will have the transistors coming soon.

At the end of the day its your money, you spend it how you want to.

 :-DD Don't say that to the wallet (as i jokingly refer to her), she might disagree.
Great news, another term for the wallet could be "Her indoors"  :-DD

I may be a bit dim but i don't get it.

Regardless i have all the replacement transistors coming, as well as diodes just to be extra sure.

Diodes are all going to be vishay 1n4005, 1 2n4037 transistor, 2 RCA 40372 and a complete set of electrolytics for the unit.

I may not get them all at once, i ordered all of it today because of it being the end of the month. Most of the capacitors are coming from arrow, some from digikey with the diodes and lone transistor. The 40372s are coming off ebay as is the transistor tester so it may be some time.

When i'm done the only originals on this board will be the resistors and two op-amps.
Her indoors, is term that is often used as a name, reference to the other half, partner, wife etc. Another one is SWMBO is She Who Must Be Obeyed

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Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #117 on: December 02, 2017, 04:45:27 am »
Well i've made some progress, the guy who replaced the transistors in '77 couldn't solder for shit. Q1 and Q2 did not have a good solder joint, the last guy damaged the  pads/traces.
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Offline Specmaster

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Re: Fluke 8400A; No display.
« Reply #118 on: December 02, 2017, 11:09:32 am »
Well i've made some progress, the guy who replaced the transistors in '77 couldn't solder for shit. Q1 and Q2 did not have a good solder joint, the last guy damaged the  pads/traces.
Good, what's the noise floor like now? I suspect that the voltage regulation is the same if you juggle the cards like before.

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Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #119 on: December 02, 2017, 07:59:45 pm »
Well i've made some progress, the guy who replaced the transistors in '77 couldn't solder for shit. Q1 and Q2 did not have a good solder joint, the last guy damaged the  pads/traces.
Good, what's the noise floor like now? I suspect that the voltage regulation is the same if you juggle the cards like before.

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I've yet to test, i figured i would wait for the last 2 capacitors from digikey before i attempted anything. I forgot them on the arrow order.
« Last Edit: December 02, 2017, 08:23:59 pm by neo »
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Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #120 on: December 04, 2017, 09:19:14 pm »
Well i got good news and really really bad news and then more bad news.

the display worked!

I think i killed part of the display.

The power supply, almost completely new parts, somehow put out -400 volts!!!

Edit: IT PEAKED AT 2KV WHERE IS THIS VOLTAGE COMING FROM?!  :scared: :scared:
« Last Edit: December 04, 2017, 09:21:29 pm by neo »
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Offline Specmaster

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Re: Fluke 8400A; No display.
« Reply #121 on: December 04, 2017, 09:26:12 pm »
Well i got good news and really really bad news and then more bad news.

the display worked!

I think i killed part of the display.

The power supply, almost completely new parts, somehow put out -400 volts!!!
This is why I was suggesting that all the parts in the power supply be replaced apart from the resistors as we know that they are correct. For all we know, this 400V symptom might have been there before temporarily and that could have resulted in the burning of of the PCB etc. 
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Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #122 on: December 04, 2017, 09:28:17 pm »
Well i got good news and really really bad news and then more bad news.

the display worked!

I think i killed part of the display.

The power supply, almost completely new parts, somehow put out -400 volts!!!
This is why I was suggesting that all the parts in the power supply be replaced apart from the resistors as we know that they are correct. For all we know, this 400V symptom might have been there before temporarily and that could have resulted in the burning of of the PCB etc.

All but 2 transistors, replaced, all but 2 capacitors, replaced. Now i think the display is doomed.
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Offline Specmaster

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Re: Fluke 8400A; No display.
« Reply #123 on: December 04, 2017, 09:28:56 pm »
There was just so many unexplained and unknown variables / symptoms with the power supply to start with and its best to start with a something that is known to be working 100% and work outwards from there.
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Offline neoTopic starter

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Re: Fluke 8400A; No display.
« Reply #124 on: December 04, 2017, 09:30:03 pm »
Well what do i do know? i think the 5s in the display are now mostly burned out.
A hopeless addict (and slave) to TEA and a firm believer that high frequency is little more than modern hoodoo.
 


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