Nanao MS9-29 (05A00585D1) dead

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Nanao MS9-29 (05A00585D1) dead

Post by frsj8112 »

I'm working on a Nanao MS9-29 for a friend.
According to the owner, the chassis was dead, does not generate high voltage.

I went through and checked caps with my ESR meter and found a bunch of caps that were out of spec.
So I proceeded with replacing all caps and got some fish smell in the room as well. So it was apparent that caps had leaked.

Connected the chassis to the tube and power supply and.....nothing.
Still the same error.
I can hear a faint HV static whine that disappears after a few seconds.
Measuring B+ starting at about 80VDC and quickly rising up to 130VDC and that's when the static whine ends.

I followed grantspain's information (many thanks for that!) back at arcadcontrols forum:
desolder pin 2 of the flyback so that it is completely isolated from the circuit board
put a mains lightbulb across ground and the track of flyback pin 2
power on and the lightbulb should power on,then meter the voltage at the lightbulb and it should be about 75 volts

if that is good then the most likely issue is on the deflection circuit or a break on one the tracks


I desoldered and isolated pin 2 of the flyback from the chassis and hooked up a light bulb (40W) to ground and the chassis track of flyback pin 2.
Connected power to the chassis and started it up.
Light bulb is faintly lit and I can measure 75VDC over the light bulb connections.
So I'm guessing that the power supply section is ok.

There were some corrosion around the vertical deflection IC, LA7837, but the connections around it seems to be ok when referencing them against a known working chassis.
I took the LA7837 from the non-working chassis and soldered it in the known-working chassis and verified that the LA7837 is working.

So this is were I'm at now.
Any guidance is very much appreciated at this moment :)
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Re: Nanao MS9-29 (05A00585D1) dead

Post by PrincessPrinPrin »

You should disable the x-ray protection and see if you have HV/picture. If you have it, there must be something that makes the horizontal drive go nuts, like the HV polypropylene capacitors on the HOT collector. You can disable the protection by lifting jumper J466 near the flyback or shorting it to the grounded jumper J467 next to it. If high voltage stays on turn power off quickly.
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Re: Nanao MS9-29 (05A00585D1) dead

Post by frsj8112 »

Thank you for your reply PPP!

I shorted J466 to J467 and hooked everything back together.
Measured B+ while starting the chassis and it started rising up to 130VDC and then there were no more static.
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Re: Nanao MS9-29 (05A00585D1) dead

Post by PrincessPrinPrin »

Static as in high voltage noise from the tube? Any sign of picture on the screen? Does the B+ stabilize itself to 75V after the static noise stops or does it remain at 130V? Neck glow? Try and disable the protection by either sucking solder off pin 14 of the LA7853 or by grounding it.
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Re: Nanao MS9-29 (05A00585D1) dead

Post by frsj8112 »

It does not sound like the typical HV-static, it's more like high pitched whine.
Screen is black
B+ stays around 130-135 VDC
No neck glow
I grounded pin14 of the LA7853 and no difference.
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Re: Nanao MS9-29 (05A00585D1) dead

Post by grantspain »

have you tested the HOT
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Re: Nanao MS9-29 (05A00585D1) dead

Post by PrincessPrinPrin »

Doesn't sound like HV shutdown. Remove the HOT and test it and while it's off circuit repeat the bulb test after resoldering pin 2 of the flyback. Check that you have the secondary voltages from the PSU, especially 24V (or close, I don't remeber exactly) on R508 and 12V on pin 11 of the 7853.
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Re: Nanao MS9-29 (05A00585D1) dead

Post by frsj8112 »

grantspain wrote: April 9th, 2020, 4:54 pm have you tested the HOT
Well I've desoldered it and diode tested it with my multimeter and it seems fine, no short circuit.
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Re: Nanao MS9-29 (05A00585D1) dead

Post by frsj8112 »

PrincessPrinPrin wrote: April 9th, 2020, 5:55 pm Doesn't sound like HV shutdown. Remove the HOT and test it and while it's off circuit repeat the bulb test after resoldering pin 2 of the flyback. Check that you have the secondary voltages from the PSU, especially 24V (or close, I don't remeber exactly) on R508 and 12V on pin 11 of the 7853.
HOT is desoldered

22.6VDC at R508
9.8 at pin11 of the 7853

Worth noting is that the 7837 is desoldered (I sacrificed it for another MS9 that had vertical collapse and bad caps (recapped)
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Re: Nanao MS9-29 (05A00585D1) dead

Post by PrincessPrinPrin »

frsj8112 wrote: April 9th, 2020, 6:28 pm HOT is desoldered
Does it test good? Meter in test diode, red on base, black on collector, expected reading around 500mV. Black on base, red on emitter, expected reading slightly higher than the former. OL with every other lead combination.

And B+ now is...?
frsj8112 wrote: April 9th, 2020, 6:28 pm 22.6VDC at R508
On both sides? This supplies the horizontal drive transformer T501.
frsj8112 wrote: April 9th, 2020, 6:28 pm9.8 at pin11 of the 7853
That's low. It comes from a 7812 regulator so it should be 12V. 7853 datasheet says it works with 9 to 13.5V though.
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Re: Nanao MS9-29 (05A00585D1) dead

Post by frsj8112 »

PrincessPrinPrin wrote: April 10th, 2020, 8:35 am
frsj8112 wrote: April 9th, 2020, 6:28 pm HOT is desoldered
Does it test good? Meter in test diode, red on base, black on collector, expected reading around 500mV. Black on base, red on emitter, expected reading slightly higher than the former. OL with every other lead combination.

And B+ now is...?
frsj8112 wrote: April 9th, 2020, 6:28 pm 22.6VDC at R508
On both sides? This supplies the horizontal drive transformer T501.
frsj8112 wrote: April 9th, 2020, 6:28 pm9.8 at pin11 of the 7853
That's low. It comes from a 7812 regulator so it should be 12V. 7853 datasheet says it works with 9 to 13.5V though.
HOT is testing fine.

B+ is 75VDC

22.6VDC on both sides of R508

Actually, when measuring the output of the 7812 regulator, it measures at 11.8VDC.
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Re: Nanao MS9-29 (05A00585D1) dead

Post by PrincessPrinPrin »

I have 11.80V on one side of R571 and 10.90V on the other side (my R571 = 94 ohm).

I would test the flyback at this point but you need a special tester.
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Re: Nanao MS9-29 (05A00585D1) dead

Post by frsj8112 »

Well i can desolder and try a flyback from one of the other chassis I have
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Re: Nanao MS9-29 (05A00585D1) dead

Post by PrincessPrinPrin »

Pics of my tests so you can compare:





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Re: Nanao MS9-29 (05A00585D1) dead

Post by frsj8112 »

Wow many thanks for the reference pics @PrincessPrinPrin

I have 9.8VDC on the same side of the resistor R571 as in your picture. On the other side of R571 i get 11.76VDC

BUT
in your picture here
PrincessPrinPrin wrote: April 11th, 2020, 8:10 pm Pics of my tests so you can compare:


with the multimeter connected to the horizontal deflection yoke connector, I have NOTHING!
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Re: Nanao MS9-29 (05A00585D1) dead

Post by PrincessPrinPrin »

Because you forgot to resolder pin 2 of the flyback.

Measure R571.
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Re: Nanao MS9-29 (05A00585D1) dead

Post by frsj8112 »

PrincessPrinPrin wrote: April 12th, 2020, 11:24 am Because you forgot to resolder pin 2 of the flyback.

Measure R571.
98.9 Ohms
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Re: Nanao MS9-29 (05A00585D1) dead

Post by frsj8112 »

Could the 7853 be bad?
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Re: Nanao MS9-29 (05A00585D1) dead

Post by PrincessPrinPrin »

frsj8112 wrote: April 12th, 2020, 12:37 pm Could the 7853 be bad?
It wouldn't explain the 130v B+. Is it still like that after resoldering the flyback pin? Check the high voltage caps on the HOT collector/H yoke. Do you have any voltage on R315 on the neckboard (HOT in place and chassis connected to tube)? Check with multimeter leads already attached to it when you turn it on.
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Re: Nanao MS9-29 (05A00585D1) dead

Post by djjimmyjames »

This is spicy 🌶
Can’t wait to hear if it works
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