Th901 broken on ms8-26A

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Pascalturbo
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Th901 broken on ms8-26A

Post by Pascalturbo » March 28th, 2020, 11:17 am

Hello,

I´ve got a nanao ms8-26A that doesn’t work actually, there is 120v on the dc plug but quite after the power is losen. No fuse blown.

I´ve found the thermistor TH901 looks broken (no value on esr tester or ohmeter).
After looking on the net I haven’t found the value or a replacement part for this component.

Does somebody have this information or had this case on the past ?

Thanks for your help !

The component in question :

Image

Image

It seems to have 0S 050 94 on reference.

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grantspain
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Re: Th901 broken on ms8-26A

Post by grantspain » March 28th, 2020, 12:51 pm

probably about 9 ohms, they all look burnt

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Re: Th901 broken on ms8-26A

Post by Pascalturbo » March 28th, 2020, 1:22 pm

Thanks grantspain,

9 ohms at 25degrees ? Its difficult to find something similar, i’ve seen it’s a 120ohm cold 25ohm at 25 degree on the ms8-29 but the ref number isn’t the same.

Perhaps i’m wrong from the start, when i push the degauss button i hear a light « clong » on the tube, despite the fact that the board doesn’t power up efficiently..
I will look also to test Q533 like you precognize.

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grantspain
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Re: Th901 broken on ms8-26A

Post by grantspain » March 28th, 2020, 1:42 pm

it will be the first of those faulty i have seen
you should check the b+ on the fuse, most likely you have a regulation circuit issue

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Re: Th901 broken on ms8-26A

Post by grantspain » March 28th, 2020, 5:59 pm

i am fixing a few of these tomorrow, i will let you know my readings

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Re: Th901 broken on ms8-26A

Post by grantspain » March 28th, 2020, 6:27 pm

NTC 5-6 ohms is what you need

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Re: Th901 broken on ms8-26A

Post by Pascalturbo » March 28th, 2020, 9:18 pm

Thank you grantspain !

I will check the B+ on the fuse to. I've soldered again the (maybe faulty) th901 to test the regulation circuit.

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Re: Th901 broken on ms8-26A

Post by grantspain » March 28th, 2020, 11:12 pm

if the ntc is reading 120ohm cold then its bad but its the first i have ever seen like this on this chassis- normally on other chassis they fracture and burn out

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Re: Th901 broken on ms8-26A

Post by Pascalturbo » March 29th, 2020, 10:39 am

No no, The ntc has no value on ohmeter, With cracks.
120ohm was a value for the thermistor on ms8-29 that i found on the net, not mine.

I’ve made some measurements :

Earth - F901 65V

ACIN - TH901 (C903 side) 112V
ACIN -TH901 (R091 side) 0V

Earth - TH901 (C903 side) 47V
Earth - TH901 (R091 side) 65V

J115 (L901 side) - Earth 65V
J115 (coil side) - Earth 45V

Q533 - ACIN 100V - 110V

It seems that the upper circuit near to the coil doesn’t receive enough voltage.
The fact that the circuit gone from 112V to 0V on the TH901 seems not normal to me.

Some NTC 5D-7(2A) and 5D-11(4A) are on the way.

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grantspain
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Re: Th901 broken on ms8-26A

Post by grantspain » March 29th, 2020, 11:33 am

you have to use a cap ground for reading any voltages, do not use any metal work

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Re: Th901 broken on ms8-26A

Post by Pascalturbo » March 29th, 2020, 12:13 pm

I´ve used the grounds on the board surrounded by dotted line, don’t know if I’m right.

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Re: Th901 broken on ms8-26A

Post by grantspain » March 29th, 2020, 1:06 pm

cap ground

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Re: Th901 broken on ms8-26A

Post by Pascalturbo » March 29th, 2020, 1:58 pm

Thanks grantspain, I’m a novice.

Cap ground is a special spot or capacitor in particular ?

I’ve used the blue circled points for the measurement.

Image

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Re: Th901 broken on ms8-26A

Post by PrincessPrinPrin » March 29th, 2020, 2:19 pm

Pin "J" is ground (for measuring B+):
J.jpg
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grantspain
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Re: Th901 broken on ms8-26A

Post by grantspain » March 29th, 2020, 2:20 pm

they are not ground

you see the 22uf cap at c909- read the b+ there, it should be 96vdc black meter lead to negative and red meter lead to positive

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Re: Th901 broken on ms8-26A

Post by Pascalturbo » March 29th, 2020, 3:52 pm

Thanks,

C909 between 0V and 4V

TH901 (R901 side) - 118V
TH901 (C903 side) - 0V

F901 118V
F902 0V

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grantspain
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Re: Th901 broken on ms8-26A

Post by grantspain » March 29th, 2020, 4:02 pm

th901 then

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Re: Th901 broken on ms8-26A

Post by Pascalturbo » April 11th, 2020, 10:01 am

@Grantspain,

Thank you so much for the value of the resistor, the board is fixed !
It needs a capkit but the problem is solved, thank to you.

Image

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Re: Th901 broken on ms8-26A

Post by yosai » April 11th, 2020, 11:57 am

Nice work! :thumbup:

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