Author Topic: HP 4274A LCR Meter - mini teardown  (Read 27331 times)

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Offline MateKrisz

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Re: HP 4274A LCR Meter - mini teardown
« Reply #100 on: June 09, 2018, 06:03:49 pm »
Ok, I solder out.
1040 hFE with a multimeter. I think it is ok.
« Last Edit: June 09, 2018, 07:04:37 pm by MateKrisz »
 
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Offline 3g57

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Re: HP 4274A LCR Meter - mini teardown
« Reply #101 on: June 09, 2018, 07:29:04 pm »
You can check the transformer in any circuit or generator
if there is a low output impedance.
U5-?
If the transformers are identical, change between them.
« Last Edit: June 09, 2018, 07:35:43 pm by 3g57 »
 

Offline MateKrisz

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Re: HP 4274A LCR Meter - mini teardown
« Reply #102 on: June 09, 2018, 07:44:49 pm »
Checking
I ordered U5 to U10 new ICs. I don't have the place to check the U5 when the card is inserted.
« Last Edit: June 09, 2018, 08:48:47 pm by MateKrisz »
 
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Offline 3g57

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Re: HP 4274A LCR Meter - mini teardown
« Reply #103 on: June 09, 2018, 09:46:35 pm »
Checking
I ordered U5 to U10 new ICs. I don't have the place to check the U5 when the card is inserted.

U5 replacement with a new one. So faster.
Just install it on the panel.
The transformer must be removed and connected to the generator.
Emulate the signal is real!
The secondary winding of the load and see the amplitude level and waveform.
If it's bad you'll notice.

I installed the Sockets!



Here is a weak spot. Therefore it can happen again.

3g57
« Last Edit: June 09, 2018, 10:01:44 pm by 3g57 »
 

Offline MateKrisz

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Re: HP 4274A LCR Meter - mini teardown
« Reply #104 on: June 09, 2018, 10:32:05 pm »
Hi,

Quick I soldered out the A3T1.
Source: 1Vrms 1kHz sin wave

Here are the results:

N2



N3



It looks good?
 

Offline 3g57

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Re: HP 4274A LCR Meter - mini teardown
« Reply #105 on: June 09, 2018, 10:40:31 pm »
not happy.
what signal at the transformer input?

Try the second one. for comparison.
Do not confuse the transformers.
« Last Edit: June 09, 2018, 10:46:30 pm by 3g57 »
 

Offline MateKrisz

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Re: HP 4274A LCR Meter - mini teardown
« Reply #106 on: June 09, 2018, 10:45:05 pm »
Source: 1Vrms 1kHz sin wave

I try the second now.
 

Offline MateKrisz

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Re: HP 4274A LCR Meter - mini teardown
« Reply #107 on: June 09, 2018, 11:09:52 pm »
Here is the A3 T2.
Source same: 1Vrms 1 kHz sin wave

N2



N3



Both transformers output similar. Both good or both bad?  :)
 

Offline 3g57

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Re: HP 4274A LCR Meter - mini teardown
« Reply #108 on: June 09, 2018, 11:10:55 pm »
You can assume that he is normal.
Two could not burn.
In this way, check the output transformers. Only necessary
load them.
 

Offline MateKrisz

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Re: HP 4274A LCR Meter - mini teardown
« Reply #109 on: June 09, 2018, 11:14:30 pm »
Good news that they are good.  Do you think as output transformer A3 T3, T4, T5?
 

Offline 3g57

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Re: HP 4274A LCR Meter - mini teardown
« Reply #110 on: June 09, 2018, 11:18:58 pm »
Good news that they are good.  Do you think as output transformer A3 T3, T4, T5?

It is necessary to check at least this way.
With a good generator and Extender boards, everything was much easier. Disconnect the input. At the input of the cascades, give the necessary signal and follow the path of the oscillograph with the oscillograph. Watch where he is lost.

p.s.  Krisz! soon morning. I'm going to go to bed.

Send me screenshots!
« Last Edit: June 09, 2018, 11:27:03 pm by 3g57 »
 

Offline MateKrisz

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Re: HP 4274A LCR Meter - mini teardown
« Reply #111 on: June 09, 2018, 11:27:50 pm »
Now I know what the extender board is good for. :) I have a Philips signal, it can everything.
Disconnect the signal, do you mean A3 J1?



 

Offline 3g57

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Re: HP 4274A LCR Meter - mini teardown
« Reply #112 on: June 09, 2018, 11:31:48 pm »
Disconnect the signal, do you mean A3 J1?

Transformer input T1.
Do not rush. Till tomorrow!
 

Offline MateKrisz

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Re: HP 4274A LCR Meter - mini teardown
« Reply #113 on: June 09, 2018, 11:43:24 pm »
Ok, tomorrow continue. Good night! :-)
 

Offline MateKrisz

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Re: HP 4274A LCR Meter - mini teardown
« Reply #114 on: June 10, 2018, 06:10:54 pm »
Hi,

I checked the BNC sockets, on the front side.It is missed from your the checklist what you wrote. All wires tested for shorts to chassis. No shorts between the pairs too.
Lc - Blue wire - OK
Lp - Red wire -  OK
Hc - Yellow - OK
Hp - White - OK

Krisz
« Last Edit: June 10, 2018, 06:59:26 pm by MateKrisz »
 
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Offline 3g57

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Re: HP 4274A LCR Meter - mini teardown
« Reply #115 on: June 11, 2018, 10:17:50 am »
Krisz! Hi!
You have another option.
Take out the module and on the table give him the necessary + 12V / -12V.
On T1, give the necessary signal. Next, with an oscillograph, look at it.
 

Offline MateKrisz

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Re: HP 4274A LCR Meter - mini teardown
« Reply #116 on: June 11, 2018, 06:56:48 pm »
Hi,

I found an interesting article about, how to test the pulse transformers. https://scienceprog.com/testing-pulse-transformer-with-an-oscilloscope/
I checked both transformers secondary n2, n3 and all right.  You see in the scope pic.
The Bias Controller arrived.
I bought U5 - U 10 ICs. I replace them, it is maybe slowly because I hate desoldering ICs from PCB. :)







« Last Edit: June 11, 2018, 07:08:03 pm by MateKrisz »
 
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Offline 3g57

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Re: HP 4274A LCR Meter - mini teardown
« Reply #117 on: June 11, 2018, 08:59:20 pm »
Signal levels are performed by U5.
This is the table.
Gives commands from the DSA- TRD DECODER.
You have a weak signal level.
Here's your task.

When you set the potentiometer signal to the maximum you do not have an error. Do I understand correctly?
It was on the video.
If you have cascaded amplifiers in good order, then you need to search for the reason with the teams!
« Last Edit: June 11, 2018, 10:34:52 pm by 3g57 »
 
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Offline MateKrisz

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Re: HP 4274A LCR Meter - mini teardown
« Reply #118 on: June 11, 2018, 09:29:31 pm »
Hi,

Today I bought U5 IC it is called LM339N and sockets. It is a good replacement?  I replace first time the U5 now. I don't have any space for the measure when the card is inserted :( May I solder on the pins of the IC little wires, but it is very homemade version... what do you think?
I tested the Bias controller, looks like it is working! :)




 

Offline 3g57

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Re: HP 4274A LCR Meter - mini teardown
« Reply #119 on: June 11, 2018, 09:42:02 pm »
May I solder on the pins of the IC little wires, but it is very homemade version... what do you think?

I did not understand the question.
What to solder?
« Last Edit: June 11, 2018, 09:43:59 pm by 3g57 »
 

Offline MateKrisz

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Re: HP 4274A LCR Meter - mini teardown
« Reply #120 on: June 11, 2018, 09:46:25 pm »
If I insert the card, I don't have any space for measuring. But if I solder short wires on the U5 339IC pins, I can measure the correct DC levels? I know it is very amateur, but I don't have extension cards yet.
The LM339N good for U5?
 

Offline 3g57

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Re: HP 4274A LCR Meter - mini teardown
« Reply #121 on: June 11, 2018, 09:51:19 pm »
You first plug in and turn it on. Will there be an error?
To solder to it is not a good option!
If you are sure that there are no problems with amplifiers and after the replacement of U5
there is an error then there is no command on U5.
The signal with U5 can be checked in the key bases Q ...... Q
They are installed at the top and they can be reached.

« Last Edit: June 11, 2018, 10:46:07 pm by 3g57 »
 

Offline MateKrisz

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Re: HP 4274A LCR Meter - mini teardown
« Reply #122 on: June 11, 2018, 11:04:40 pm »
I am replaced the U5 but nothing changed. ERR 4 still flashing. Do you think Q2 to Q5?

Krisz
 

Offline 3g57

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Re: HP 4274A LCR Meter - mini teardown
« Reply #123 on: June 11, 2018, 11:11:05 pm »
Maybe. It is necessary to change.
It is desirable to measure the levels c U5.
U5 adjusts the signal level at the output U2.
R14 at the output U1.
How do I remember the output of U1 was close to normal?
« Last Edit: June 11, 2018, 11:17:30 pm by 3g57 »
 

Offline MateKrisz

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Re: HP 4274A LCR Meter - mini teardown
« Reply #124 on: June 11, 2018, 11:17:21 pm »
Ok, I try to measure the transistors. :) What level need there?
I not measured yet the U1 output voltages.
« Last Edit: June 11, 2018, 11:23:50 pm by MateKrisz »
 


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