Viewsonic E653 Monitor. Squashed picture II

Seems to me that the advice being given on that forum, whilst not definitive, is never-the-less exactly right. I would suggest that the first thing to do would be to check the pincushion amp, and its drive. Also, if any caps *have* leaked (and you are not confusing the glue that's often found around their bases, with leaked electrolyte), then they need to be replaced. Just because they had enough go in them to just about do their job three days ago, doesn't mean that one of them hasn't gasped its last today.

To use a car analogy, you can drive around today with half a millimetre of lining material on your brake pads, that stop the car today, and squeal metal on metal tomorrow ...

The 24C08 is an EEPROM, where all of the setup parameters are stored. It's not at all unusual for these to get corrupted in TV sets, and to produce symptoms like you describe, which are not correctable. However, it's often necessary to pre-program a new blank one with a basic set of parameters, before it will work.

Finally, a warning. If you are not used to working on monitors, take extreme care, as they employ switchmode power supplies, which are (literally) potentially lethal. Also the high voltage generation circuits for the CRT can give you a nasty bite, as can the CRT itself, long after you have switched off.

Arfa

hi and thanx for your reply.....

i'm sorry my post didn't show the fourth chip which is;

1. KA3842B and also there was a fifth one...... E009C i wrote it's data on the back of the paper containing all the data of the chips i found, it's data are;

1. PM02AF LM this one i couldn't get any datasheet about 358N

the fourth chip is smps controller, this makes me know only three out of five chips and i don't know exactly which is the pincushion amp, or where is it's drive. it's kind of making me handicaped not having the service manual for this piece of hardware. also i don't have the proper test equips, only an avo meter, the data sheets and my personal experience.

today i replace the caps that i suspected of having leaked, and the truth to be said, the pincushion became less by 8mm which is small but positive result. also i tried to replace the ATMEL 24C08 EEPROM with a new blank one, but i got a white screen with horizontal bright lines across it, it looked like a writing paper and i didn't see any thing but shadows of what really was to be shown behind this new look so i turned back to the old one and every thing is fine relatively.

the first chip i mentioned "no. 1" is a big ic and since the begining i suspected it but i don't have it's data sheet as to decide whether or not to replace it. also it's said to be discontinued which makes me unsure whether will i find it on the market or not.

as a matter of fact the monitor is eight years old and all of it's capacitors are probably if not surely much older, so it needs all of it's caps to be replaced. but i need to have it working as not to be throwing mony away for nothing.

you are right about being extra careful while working with this type of hardware, but the smps isn't what i fear. what really makes me sweat my juices out is the tube itself, when i'm working on it while online i know that there is a 25+ kv infront of me. one mistake and i might be history and so i take emergency precautions while working with it. also i have proper grounding which calms me down a little.

this is all i've got,

hope for the best solution.

thanx all

--
Message posted via ElectronicsKB.com
http://www.electronicskb.com/Uwe/Forums.aspx/repair/200808/1

Looking at

there are a lot of entries for Viewsonic manuals. I only had a quick skim through, but there seemed to be lots of listings for the e655 model which might be sufficiently similar to work by ??

The pincushion amp is likely to be discrete rather than a chip, and might be based around FET on a small heatsink. Geometry correction waveforms are often fed to it from that 'big' chip. I fear that you will not get too far on this fault without a 'scope to look at the waveforms. I would absolutely recommend against employing any kind of 'shotgun' approach at component replacement, as you are likely to end up with more problems than you started with.

As for the safety angle, I think you might be misunderstanding the relative dangers of the HV generator circuitry, and the power supply. Whilst it is true that the CRT's final anode will have around 25 kv on it, the source impedance for this supply is relatively high. This means that the available current at that voltage is quite limited. For sure, if you had a weak heart, or managed to hang yourself right across that supply, receiving a shock from it *might*, at a pinch, prove fatal. The much more likely outcome is a stinging hand - probably with a cut across it where your hand collided with the chassis during its rapid exit :-) - some words that are completely new to your children :-) and wounded pride.

On the other hand, the switch mode power supply has around 380v dc on its front end, and this is derived DIRECTLY from the incoming line voltage by a bridge rectifier, so a relatively low impedance source with the current limited *only* by the front end fuse, which is likely to be a 3 or 4 amp ceramic type. This is enough to kill you. No joke. Fact.

So please take care around that area. Use an isolation transformer if you have one. Makes life a little bit safer.

Arfa

hi

this is today's update...

i actually took the ridiculous desition of replacing all the electrolitic caps as they are the first suspect of any damage to an old circuit. nothing really changed, i think that the image quality increased but i'm not sure. i also replaced ic no. 5 because while googling i found some datasheet that says it's a dual op-amp so i thought that this would be the culprit, but nothing so far.

an oscilloscope is a very very nice tool to have, but actually i'll be stuck for a long while with the shotgun policy -which worked with me several. as you are more knowledgable than me about monitors, i'll imagine that you're a psychic and you can see inside my pistol and tell me whether the bullet is close or far. i'll tell you all the details you need, you only have to give the directions.

actually i don't have children, so don't worry about whatever vocab -i'm not a minor either :-).

i'll follow this post with another listing all the discrete large triple legged comonents, whether with heatsinks or not. and i'll try to google thier datasheets also so stay tuned.

also please try to reply earlier because i waited for your opinion today morning, and it could have taken a good part in my desition.

ok...

bye.

--
Message posted via ElectronicsKB.com
http://www.electronicskb.com/Uwe/Forums.aspx/repair/200808/1

Em,. Two thoughts one look for a big diode in front of the line output transistor or close to the Line OutPut Transformer. When these break down, they cause the width to go out.The screen gets really wide.

If the screen height is collapsing maybe check for something like a TDA1675 and associated components, in particular diodes.

Best regards,

Robin

this is the follow up with the discrete transistors i found inisde the monitor. there are exactly five components of this description, three are FETs and two are BJTs, and all the rest transistors inside are small TO-92 BJTs, all of them are BJTs. the FETs are all near the power collection, one just right after the big 220uf/400v cap and it have a big heatsink, i guess it's a chopper, the second looks nearly the same and is located just beside the smps transformer, i guess it's a chopper too. the last one is without a heatsink and is locate nearer to the tube connectors.

BUT on the other hand the BJTs are locate just beside the tube connectors, particularly beside a plug that is 1x4 grid of connectors, the wires in it are brown-yellow-blue-red from right to left. so i guess one of these transistors or both of them are responisble for what happened.

thier numbers are;

1. C5248 2. 0669A both of them are NPN

the one FET that is near the tube connectors is;

1. 1RFG30

i googled for datasheets, the only one i found was no. 1's datasheet, it states that it's "High-Voltage Switching (Audio output amplifier transistor, stabilized power supply transistor)" and i think this is the one. the thing is i tested the BJTs and they seemed to be operational, i'm not sure but i know how to test a BJT with an avo meter.

also the no. 1 transistor is attached to a metal frame mounted on the pcb with tin solder, rather than attached to a heatsink.

i'll try to replace them and see what happens, i hope i find them all on the market. i don't know what viewsonic was thinking, manufacturing it's products with these ancient components. it seems as they manufactured these things in the ice age, then stored them into the ice, and when the ice melted by the global warming, they got them out and began selling.

whatever..........

as for the image, actually it's not collapsed i'd rather say that it's widened but not so much. it looks like a chair that someone was sitting on then stood and the cushion on the chair didn't return back to it's normal shape. it just stayed compressed inside, the image just looks like that, with it's outer corners wider than the middle and spreading outside the view. they call this simptom pincshion effect, also if you were following the horizontal size doesn't have any effect whatsoever.

actually there is that diode just after the smps transformer but i don't know exactly if it is operational or not as it didn't grab my attention. i'll check on it in the morning.

thanx for the ideas

--
Message posted via ElectronicsKB.com
http://www.electronicskb.com/Uwe/Forums.aspx/repair/200808/1

The Diodes after the the SMPSU are secondary rectifiers, they're most probably ok.

You are looking for a big diode like this:

near the line output transistor, this is the transistor most likely screwed to the aluminium box/heatsink surounding the line output transformer.

I have seen this diode fail, in a few monitors, when it fails it effects width and east/west correct,(pincusion). All this said its been at least 10 years since I was fixing monitors.

Good luck,

Robin

i red this paper which gave me an idea about the larger picture of horizontal sync.

and i think it said the same as you suggested, there is a problem with a peripheral component around the flyback transformer. i also checked on the flyback trans. and the components around it, i found the damper diode and it checked right it's operational, but it looks like a regular diode except for it's a little bulky and brownish in color. i found also another diode that looks like the one the datasheet you posted mentioned, it has a glass casing and it's oval in shape but it's very small and white and it's operational too.

the numbers of both the diodes are;

1. rg4a bulky one 2. 33ipn small one

finding that every thing is fine with these, i tried to check every component around the flyback transformer. every thing checked ok, nothing seemed damaged, there were two more diodes and they were ok, there was a coil and it checked ok too. and a n-p-n BJT and it checked ok too. an elecrolytic capacitor was there too and it was fine, but i'll recheck on it again may be replace it, i already got a new spare one.

not only this i checked on all the FETs on the pcb and they all were n- channel type and they were fine. i have diode checker in my multi-meter and it shows the biasing voltage if the diode is operational. all of the solid state devices i've checked were ok. all the BJTs around were ok too, and the diodes that were away from the flyback transformer were ok too. everything just looks fine, no burnes, no exploding or leaking devices, or damaged not even a small resistor, which adds much to my confusion. does this have any thing to do with damage to the flyback trans. itself?

hope any solution that fixes this situation appears in the horizon.

thanx

--
Message posted via ElectronicsKB.com
http://www.electronicskb.com/Uwe/Forums.aspx/repair/200808/1

sounds likey... They are not always in that round package, sometimes the are just large cylndrical types same pagage as a large rectifier.

If it isnt the diode.. then maybe one of the big pulse caps...

Unless you have an ass kick component tester, and I'm gussing you don't, substitution is the only way to prove them good, this is where having a huge box full of old monitor boards would come in handy... ;-)

Good Luck

Robin

To be honest, I think that you have reached the point where you can't go much further without a set of schematics and a 'scope. You need to see how E-W raster correction modulation is achieved, and then to see why it's not happening. It's usually not quite as straightforward on computer monitors, as it is on a TV set. This is because the TV set runs at a constant line rate, so only one condition needs to be corrected for, whereas a monitor has to run at a number of different line and frame rates. As the line rate changes, so does the tuning of the flyback transformer, and the deflection yoke. This results in major width and geometry variations. To compensate for all these conditions, the E-W correction often takes the form of a FET modulator stage for the line output HT supply. This is driven from the sync processor and timebase chip (often a big one at the front of the chassis) which draws its correction data from the EEPROM. When you change the parameters via the front panel user controls, these are stored back in the EEPROM by the same chip. Brightness and contrast data are also stored in here, as well as auto grey scale and beam current data, which is why the new blank chip that you tried, didn't work.

I don't know what else to suggest that you do. Did you look on eserviceinfo.com to see if the Viewsonic with almost the same model number that's listed, was similar ?

This site claims to have the e653 manual for free, but they need you to sign up for their newsletter

Arfa

He may just be lucky if he finds the Fet or darlington which drive the EW-correction and if this is shorted. Often there is an inductivity in the collector path to block horizontal frequency - this may be burnt then, too, sometimes opened.

Good explanation.

I was often surprised to find almost identical modules in different models :-).

Regards, H.