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Author Topic: Tektronix 2232 scope.... in need of a doctor..  (Read 2051 times)

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Online tautech

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Re: Tektronix 2232 scope.... in need of a doctor..
« Reply #75 on: June 20, 2017, 07:13:06 AM »
As you complete this repair I would have the inductance of each winding measured and note it in this thread.
As time goes by these SMPS transformers will get harder to source but if each windings info is known and can be matched with n# turns, wire gauge and core parameters it shouldn't be hard to replicate DIY.

Who knows, you might even be able to start a little sideline making these and supplying the market.  :)
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Offline Vince

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Re: Tektronix 2232 scope.... in need of a doctor..
« Reply #76 on: June 20, 2017, 07:24:40 AM »
As you complete this repair I would have the inductance of each winding measured and note it in this thread.
As time goes by these SMPS transformers will get harder to source but if each windings info is known and can be matched with n# turns, wire gauge and core parameters it shouldn't be hard to replicate DIY.   

My intention/thoughts exactly !  :)

I have ordered two coils. Will repair my scope with one of them, so I can fix it quickly, and I will use the second coil to take inductance measurements .... later.... because I don't have an RLC meter just yet ! ... and no money to buy one, have much higher priorities on my plate currently...
Well, until I can afford a decent/good RLC meter, maybe I can get a cheap/crap one for a few tens of bucks, just to get an idea...


Quote
Who knows, you might even be able to start a little sideline making these and supplying the market.  :)

LOL  Well I would have to sell an awful lot of them, and for a lot of money in order to make it worth the time spent winding... plus, since all the specs would be freely available on this forum, anybody could do the same as me, and profits would plummet ! LOL

But I will try and make myself a new coil, sounds like fun, I want to do that... at least once in my life. I find it educational... and being abel to buld your own stuff to repair your old gear, rather than buying old parts that eventually will run out anyway.... I find it satisfying.
« Last Edit: June 20, 2017, 07:58:37 AM by Vince »
 

Offline oldway

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Re: Tektronix 2232 scope.... in need of a doctor..
« Reply #77 on: June 20, 2017, 08:17:49 AM »
Quote
Might buy two of them just in case I get unlucky and one of them is "noisy", as he states.
Most of them are noisy because they are faulty. When inductance is too low (internal short circuit between turns or layers) , there are high peaks currents who are stressing the ferrite core to saturation and the noise is coming from sub harmonics of magnetostriction of the core.

Quote
...and I will use the second coil to take inductance measurements .... later.... because I don't have an RLC meter just yet ! ..
How to measure an inductance without RLC meter when you have a function generator with counter, a capacitor of known value and a working oscilloscope ?
This is very easy, I let you guess the answer......
 

Offline Vince

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Re: Tektronix 2232 scope.... in need of a doctor..
« Reply #78 on: June 20, 2017, 08:46:31 AM »
Most of them are noisy because they are faulty. When inductance is too low (internal short circuit between turns or layers) , there are high peaks currents who are stressing the ferrite core to saturation and the noise is coming from sub harmonics of magnetostriction of the core.

hmmm, thanks for that   :)  So I can just measure the resistance (now I have the data from my old coil) of the windings to see if they are shorted or not...

Quote
How to measure an inductance without RLC meter when you have a function generator with counter, a capacitor of known value and a working oscilloscope ? This is very easy, I let you guess the answer......

A resonant circuit yeah why not... I am rusty on the theory/math though, I must admit... I will dig out my old text books...   1/2*PI*sqrt(LC), something like that... shame on me. I mean I studied this stuff 20 years ago, and zero practice since then... yes of course I got rusty !  :(  No worries, I will get my old text books and refresh my memory  ;)

I don't have a counter BTW   ;)  My TDS 544A can measure frequency though, obviously...

I have a 1Mhz analog generator, and a 2MHz "DDS" Fluke arb gen but it's in pieces... I am in the process of replacing the original LCD, with a back lit unit, because the original LCD has no backlight and it's just a real pain to read...

Anyway, I could also just wire up on a bread board, a simple first order RL filter, look for the 45° phase shift / 1/sqrt(2) amplitude reduction (the TDS544A could help with its automatic measurements) and figure out what value L is...

Well OK, in practice it would not be as accurate as measuring the frequency of a resonant circuit, I admit...

OK OK....I will do a resonant circuit.  Google refresh my memory please !

https://www.electrical4u.com/resonance-in-series-rlc-circuit/

Yeah, phew, I was correct earlier, 20 years of inactivity have not erased everything just yet, I am not as hopeless as I thought...
« Last Edit: June 20, 2017, 08:52:23 AM by Vince »
 

Offline oldway

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Re: Tektronix 2232 scope.... in need of a doctor..
« Reply #79 on: June 20, 2017, 08:55:04 PM »
Quote
So I can just measure the resistance (now I have the data from my old coil) of the windings to see if they are shorted or not...
A short circuit between turns does not change the coil resistance enough to be measured and detected. But the inductance is reduced and even more the damping factor of the inductor associated with a capacitor in a RLC parallel ressonante circuit.
The short circuited turns works as a short circuited secondary of a transformer.
The definitive diagnostic is made "in circuit working" by measuring the current waveform on the shunt resistor and to compare it with waveform of service manual.
 

Online tautech

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Re: Tektronix 2232 scope.... in need of a doctor..
« Reply #80 on: June 21, 2017, 03:51:00 PM »
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