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Discussion Starter · #1 ·
I think I toasted my H deflection coils!!! The second H OUT 4288 is gone now, so I search the problem and messured only 0,5 Ohm on every H coil! I think this is no good news for me, the V coils read about 10 Ohm!

Are the H coils OK, or not??? Anyone mesured the coils from a 10PG??? The 9PG should not be much different!

I think have to search 3 deflection coils for my 10PG, someone sell me three coils????:confused:

Thanx,

Daniel
 

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NO, that's not it. 0.5 ohms is normal I've never seen a yoke coil burn or short on a CRT. Check your damper diodes around that transistor...


Curt
 

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Discussion Starter · #3 ·
Oh thank you Curt!!!!

for that good news, yesterday I droped my soul in beer, to forget about the H coils, but got your message now, and I'm happy again....thanx:)

Curt, I checked the diodes D205 and D206, they are OK! :confused:

R220, R220A and R221, all OK!

Something caused the H Out Transistor to get hot, and then burned up!!!

The pj worked for 30 seconds with the second 4288A, yes and I saw the raster on the tubes faces, it was very small, but hight was nearly normal! I turned the H Out and H widh pots fully counterclockwise, I thougt this is zero:confused:

before I powered up, so I think the raster looked OK???

What drives my H Out transistor to death?

I had the Q207 and Q208 checked, Q213 and Q215 all OK! Can't find another part burned on the deflection board, all seams to be ok, exept my 4288A!!!! So I thought about the coils, but if 0,5 Ohm for them is normal........I will take out the defl. board again:confused:

Thank you,

Daniel
 

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As I recall we are dealing with a 10 PG so I'm not sure if this is the same, but after replacing the output transister and turning on the projector again, connect a digital VOM and set the H-width pot to 1.8 V + or- 0.1 V. This is for a 9PG.


Chip S.
 

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I've also had bad 2SC 4288A transistors, if the replacement was an off-brand, try another brand.


If you get stuck, I can exchange you for a working board.


Curt
 

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Discussion Starter · #6 ·
Curt,

yes the subsitude was a off-brand transistor, but 2SC4288A! Will order now some (10) TOSHIBA, hope they will work better!!!!

What about the 2SC4290A???? Its also a Si-N transistor, 1500V, 200W, but 20A instead of 12A!!! Perhaps it is the real thing for the sensible NEC?

Later,

Daniel
 

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Another possibility are the 2 big capacitors that couple the coils. I think 33uF at 250v or somewhere about there.


Marc
 

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Discussion Starter · #8 ·
Marc,

desoldered the two 33uF 200V caps, they are OK. One reads 31,2uF the other 30,5uF, on both isolation is over 32MOhms!

I think thats not the problem, but noticed some differences in the three schematics PG-9000, PG-100000 and PG-9200! The H output stages differ in the connections of these two caps C5040 and C5041.


PG-9000: caps are direct coupled with the chokes T5001 and T5005

PG-10000: caps coupled only at T5005, R5079 is between the two chokes

PG-9200: same as 10PG, but added a cap C5402 22000uF parallel to R5079


My PWB was a 10PG, but someone changed the layout back to the 9PG schematic. Did NEC that, anyone please have look to their 10PG board, is it changed too?


Perhaps its an upgrade to put it back to the 10PG, and than solder that C5402 22000uF V? over the R5079 :confused:

Thank you all,

Daniel


still wait for the Toshibas!
 

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22000µF ???

Really


Roland
 
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