need help with odd CRT monitor image

it's

n
4

mp

lem

o a

r.

ard

wo

it

ace

?

.

er goes anywhere near 24 volt. there is a .5 volts poorly defined waveform, almost looks like ripple. im thinking it should be a 24v sawtooth? i am th inking something on the board may be pulling down pin 7?

just to be clear, the pin 7 is 1/2 volt(.5) ripple like form

thanks

Reply to
mhooker32
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it's

n
4

mp

lem

o a

r.

ard

wo

it

ace

?

.

er goes anywhere near 24 volt. there is a .5 volts poorly defined waveform, almost looks like ripple. im thinking it should be a 24v sawtooth? i am th inking something on the board may be pulling down pin 7?

You can't check this diode with a dmm... I posted above:

"I didn't read back through all the posts, but if you haven't, check the pu mp up diode. The anode will be connected to the Vcc and the cathode to the pump up pin of the vert IC. A weak diode here will cause all sorts of hav oc (don't check it with a dmm - they often sag under load)."

Reply to
John-Del

The DSE one has a comparator rigged to generate spike pulses - the ringing pulses clock a logic 1 along a shift register and basically counts how many times the inductor rings.

The schematic is floating about the web, and there's nothing hard to find in the parts list.

Reply to
Ian Field

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Reply to
Foxs Mercantile

i swapped the D360 diode with another from the board, no difference. i dont really understand from the schematic what the pump up circuit is. it has 2

4V thru a electrolytic cap in series to pin7 . is that an input or an outpu t? the same circuit( before the cap) goes to pin 3. there is only about 1/2 volt on pin 7. is it supposed to pulse, pin 7 pulling down the 24 v?
Reply to
mhooker32

That is a most interesting point, the 1N4937 diode is indeed a fast switching diode and it certainly appears to be critical for building the vertical deflection. Your point about sagging under load could indeed be correct for this problem as described by the OP.

Learn something every day, thanks!

John :-#)#

Reply to
John Robertson

There's sometimes an electro with ambiguous purpose (also on audio amps). It bootstraps the output to the bias network for the output transistor bases. Its almost positive feedback that reduces drive current requirement for the output pair and improves linearity.

Reply to
Ian Field

just replaced the vertical deflection IC LA7851. same image, no better. regarding d360 possibly sagging, i did swap it with another on the board, and it was the same. i'll have to keep digging, but any help is appreciated.

thanks

Reply to
mhooker32

egarding d360 possibly sagging, i did swap it with another on the board, an d it was the same. i'll have to keep digging, but any help is appreciated.

Not much left...

Try warming up the board with a hair dryer on high or a heat gun on low and watch the picture as you do. I'd bet dollars to donuts at this point that the picture stretches out. You said you recapped the monitor but was this all the larger electros that are known to cause issues (like a kit) or *ev erything*. There are often low value electrolytics back at the signal gene rator side used for signal coupling that get juicy on the bottom and cause issue either from low esr (they can be juicy and still check OK) or from co nductive contamination from the leaked electrolyte.

If the heat doesn't expose a lazy high esr coupling cap, then try washing t he board with a suitable cleaner and acid brush, removing the "jungle" IC i f need be but otherwise clean between all the leads.

Reply to
John-Del

regarding d360 possibly sagging, i did swap it with another on the board, and it was the same. i'll have to keep digging, but any help is appreciated .

nd watch the picture as you do. I'd bet dollars to donuts at this point th at the picture stretches out. You said you recapped the monitor but was th is all the larger electros that are known to cause issues (like a kit) or * everything*. There are often low value electrolytics back at the signal ge nerator side used for signal coupling that get juicy on the bottom and caus e issue either from low esr (they can be juicy and still check OK) or from conductive contamination from the leaked electrolyte.

the board with a suitable cleaner and acid brush, removing the "jungle" IC if need be but otherwise clean between all the leads.

well, im starting to think that its going into HV shutdown, and rather than shutting down, the half scan is how it was made to shutdown. still, doesn t shutdown usually not shut down the vertical scan ? i dont think anythin g on this unit is the usual. the manual for it is near useless, very little info. another thing, the schematic shows two pairs of jumpers, for 13 or 1

9 inch use. both pairs are jumped on this board, and the same board on eba y has both pairs jumped. its a hair puller. pin 13 on the 7851 is the x ray protection pin, and it needs to be a specific voltage or the chip shuts do wn. the manual says that, but doesnt say the voltage. im going to end up b uying a chasssi, but i'd still like to know what the heck is wrong with min e.

thanks

Reply to
mhooker32

r. regarding d360 possibly sagging, i did swap it with another on the board , and it was the same. i'll have to keep digging, but any help is appreciat ed.

and watch the picture as you do. I'd bet dollars to donuts at this point that the picture stretches out. You said you recapped the monitor but was this all the larger electros that are known to cause issues (like a kit) or *everything*. There are often low value electrolytics back at the signal generator side used for signal coupling that get juicy on the bottom and ca use issue either from low esr (they can be juicy and still check OK) or fro m conductive contamination from the leaked electrolyte.

ng the board with a suitable cleaner and acid brush, removing the "jungle" IC if need be but otherwise clean between all the leads.

an shutting down, the half scan is how it was made to shutdown. still, doe snt shutdown usually not shut down the vertical scan ? i dont think anyth ing on this unit is the usual. the manual for it is near useless, very litt le info. another thing, the schematic shows two pairs of jumpers, for 13 or 19 inch use. both pairs are jumped on this board, and the same board on e bay has both pairs jumped. its a hair puller. pin 13 on the 7851 is the x r ay protection pin, and it needs to be a specific voltage or the chip shuts down. the manual says that, but doesnt say the voltage. im going to end up buying a chasssi, but i'd still like to know what the heck is wrong with m ine.

When projection TVs started hitting the market, manufacturers soon learned that a scan loss in either direction would immediately destroy the CRTs. I n response, manufacturers learned to not start the HV until both deflection s were established, and shut down same if one was lost or even diminished b y a fixed percent. The point is that a vertical collapse would not be the result of a shutdown, but a cause.

Read my previous post again. One of the last CRT TVs I worked on was a Zen ith 35" console with a stubborn vert (slow to fill, weird linearity issues) . It turned out that the board became conductive from leaked electrolyte a nd dust. Heating and cooling the board affected the deflection, but no com ponents were themselves temperature sensitive. I ended up pulling the flyba ck, smps transformer, and any inductor that looked like it could hold water and immersed the whole board in a parts cleaner. Once assembled, the vert ical was perfect and didn't drift.

Reply to
John-Del

:

ter. regarding d360 possibly sagging, i did swap it with another on the boa rd, and it was the same. i'll have to keep digging, but any help is appreci ated.

ow and watch the picture as you do. I'd bet dollars to donuts at this poin t that the picture stretches out. You said you recapped the monitor but wa s this all the larger electros that are known to cause issues (like a kit) or *everything*. There are often low value electrolytics back at the signa l generator side used for signal coupling that get juicy on the bottom and cause issue either from low esr (they can be juicy and still check OK) or f rom conductive contamination from the leaked electrolyte.

hing the board with a suitable cleaner and acid brush, removing the "jungle " IC if need be but otherwise clean between all the leads.

than shutting down, the half scan is how it was made to shutdown. still, d oesnt shutdown usually not shut down the vertical scan ? i dont think any thing on this unit is the usual. the manual for it is near useless, very li ttle info. another thing, the schematic shows two pairs of jumpers, for 13 or 19 inch use. both pairs are jumped on this board, and the same board on ebay has both pairs jumped. its a hair puller. pin 13 on the 7851 is the x ray protection pin, and it needs to be a specific voltage or the chip shut s down. the manual says that, but doesnt say the voltage. im going to end up buying a chasssi, but i'd still like to know what the heck is wrong with mine.

d that a scan loss in either direction would immediately destroy the CRTs. In response, manufacturers learned to not start the HV until both deflecti ons were established, and shut down same if one was lost or even diminished by a fixed percent. The point is that a vertical collapse would not be th e result of a shutdown, but a cause.

enith 35" console with a stubborn vert (slow to fill, weird linearity issue s). It turned out that the board became conductive from leaked electrolyte and dust. Heating and cooling the board affected the deflection, but no c omponents were themselves temperature sensitive. I ended up pulling the fly back, smps transformer, and any inductor that looked like it could hold wat er and immersed the whole board in a parts cleaner. Once assembled, the ve rtical was perfect and didn't drift.

this board is so clean you could eat off of it. im also looking into that it may be lacking the pulse feed from the flyback to the vert ic.

Reply to
mhooker32

If the high voltage section shuts down you would lose the brightness of the electron beam, no? Sounds from your description the electron beam is clearly visible when the deflection collapses.

--

Rick C
Reply to
rickman

r. regarding d360 possibly sagging, i did swap it with another on the board , and it was the same. i'll have to keep digging, but any help is appreciat ed.

w and watch the picture as you do. I'd bet dollars to donuts at this point that the picture stretches out. You said you recapped the monitor but was this all the larger electros that are known to cause issues (like a kit) o r *everything*. There are often low value electrolytics back at the signal generator side used for signal coupling that get juicy on the bottom and c ause issue either from low esr (they can be juicy and still check OK) or fr om conductive contamination from the leaked electrolyte.

ing the board with a suitable cleaner and acid brush, removing the "jungle" IC if need be but otherwise clean between all the leads.

than shutting down, the half scan is how it was made to shutdown. still, d oesnt shutdown usually not shut down the vertical scan ? i dont think any thing on this unit is the usual. the manual for it is near useless, very li ttle info. another thing, the schematic shows two pairs of jumpers, for 13 or 19 inch use. both pairs are jumped on this board, and the same board on ebay has both pairs jumped. its a hair puller. pin 13 on the 7851 is the x ray protection pin, and it needs to be a specific voltage or the chip shut s down. the manual says that, but doesnt say the voltage. im going to end up buying a chasssi, but i'd still like to know what the heck is wrong with mine.

he

i put a probe on pin 4 of LA7851, the vertical deflector ic chip. its a pul se from the AFC terminal on the flyback. there is virtually no pulse, just a half volt . from the flyback afc terminal, i get a 90 volt shape that lo oks like a half rectified sine wave, just the top of the sine wave. 90 vol t seems low. i think there has to be a pulse at pin 4 for the IC to operat e. i bought a working chassis on ebay, and will check some pins outputs, i dont want to give up now.

Reply to
mhooker32

The number sounds familiar - but its been a while.

some vertical chips were just the power stage while others included the ramp generator etc. If it does and you've tried replacement, you might need to consider what was said about shorted turns on the yoke.

Some of the passives can cause trouble, but they're easier to test than shorted turns.

Reply to
Ian Field

Its a fairly common type number - I've certainly encountered *MUCH* less reliable diodes along the way.

Not that I've never had to replace one, but they're not prominent in the stock faults list.

Reply to
Ian Field

It that is a working chassis for that board it would be great if you can photograph the 'scope images and post them somewhere. I can capture them and add to flippers library of tech tips for folks to use in the future...

John :-#)#

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Reply to
John Robertson

Oddly enough I've had to replace every 1N4002 diode used in one home pinball game from the 1970s (Fischer's Sky Hawk) because they fail at random. They appeared to be the world's cheapest diode - early Chinese?

- the body isn't a smooth cylinder rather it is lumpy.

I have to agree that diodes in monitors rarely fail, I can't recall the last time we traced a problem to a faulty diode.

Now pinball power supplies? Those we replace diodes from time to time...

John :-#)#

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Reply to
John Robertson

I never did understand why they make a series of diodes like the 1n4001 to 1n4007, each with a higher voltage rating. My only thought is they make a batch like the microprocessors and test each one to see its maximum rating and mark the lesser ones at a slightly lower price. I do think the 1n4007 may be a slightly different kind of makeup than the others. Another thing is odd voltage cpacitors like a 63 volt unit. Why not just 60 or 70 or even 65 due to the large tollorance of them.

Reply to
Ralph Mowery

There was a European BA prefix family of diodes that I can't remember the numerical bit that were seriously dodgy.

There was a block package E/W diode that could be single or double and had an SK prefix (IIRC) that I routinely replaced whether they'd failed or not.

Not many in monitors - nearly all in TVs.

Reply to
Ian Field

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