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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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Magnavox RH8524 Blue shifted left
Hi,
The blue picture has shifted left on my old projection TV. At one point, this only occured when the TV was cold and would clear up. I can test components and replace them however the actual circuitry doesn't make sense to me. Any ideas? Thanks! Kirk S. |
#2
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Magnavox RH8524 Blue shifted left
Thanks...
And which board would that be? I already did that to an interconnect board. Some solder joints looked iffy on it. If you could give me a general idea what to look for. I suppose it would be before the signal is fed to each of the different CRT boards, eh? Kirk S. P.S. got any idea where I can find service literature? A schematic with labeled areas really helps me out! "Ol' Duffer" wrote in message ... In article , says... The blue picture has shifted left on my old projection TV. At one point, this only occured when the TV was cold and would clear up. I can test components and replace them however the actual circuitry doesn't make sense to me. I'd have a look at the convergence board. Early versions were especially prone to intermittant connections. They thought they could get away with shoving square pins through the board instead of using plated-through holes. Haven't seen one of these relics in awhile, but it used to be pretty routine to suck off the old solder and re-do all the pins. |
#3
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Magnavox RH8524 Blue shifted left
On Sun, 08 Aug 2004 20:44:14 GMT, "Kirk S."
wrote: Hi, The blue picture has shifted left on my old projection TV. At one point, this only occured when the TV was cold and would clear up. I can test components and replace them however the actual circuitry doesn't make sense to me. Any ideas? Thanks! Kirk S. If there is blue shift to the left, the TV must be travelling in that direction. Check to see if there is red shift on the right. |
#4
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"Ol' Duffer" wrote in message
... In article , says... And which board would that be? I already did that to an interconnect board. Some solder joints looked iffy on it. If you could give me a general idea what to look for. I suppose it would be before the signal is fed to each of the different CRT boards, eh? On most sets it's in front, behind the speaker cover, on a panel that's held closed with 2 or 4 screws, opens down for access to several dozen pots. Thanks... I've got my solder sucker and soldering station ready... I'll keep away from the pots. I've got an isolation transformer and o-scope. I've used the scope on digital circuits however the voltages inside a tv set concern me. Worried about hooking the probe to a live circuit and smoking something... My iso is only good for 1amp anyway. Actually, convergence on these sets is a separate, parallel signal path. Each yoke has two sets of windings. Bulk deflection comes from one set of V/H drive circuits on the deflection board. Smaller correction signals come from 3 sets of drive circuits on the convergence board. I'll poke around those boards looking for questionable solder joints on the connectors. I find it a lot on the arcade boards I tinker with. Since I have blue deflection, I would bet it is the convergence board. The pots also sound like a likely place to look for trouble. P.S. got any idea where I can find service literature? A schematic with labeled areas really helps me out! Used to be available from Philips (for a price). May be out of print by now. I don't think Sams ever did RPTV. If you're good at sucking up, maybe the local service center will make a Xerox for you(?) Found a set at www.servicemanuals.net . The only problem is that the parts all have some manufacturers code on them. Voltages and general information should make it easier to find what I'm looking for. Thanks a bunch! TV works pretty good, I got it free by simply hauling it off for someone. The internal battery is dead as well. Brightness is a bit low. Perhaps it is time to change the fluid. Kirk S. In article , says... The blue picture has shifted left on my old projection TV. At one point, this only occured when the TV was cold and would clear up. I can test components and replace them however the actual circuitry doesn't make sense to me. I'd have a look at the convergence board. Early versions were especially prone to intermittant connections. They thought they could get away with shoving square pins through the board instead of using plated-through holes. Haven't seen one of these relics in awhile, but it used to be pretty routine to suck off the old solder and re-do all the pins. |
#5
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"Ol' Duffer" wrote in message
... In article , says... Thanks... I've got my solder sucker and soldering station ready... I'll keep away from the pots. I've got an isolation transformer and o-scope. I've used the scope on digital circuits however the voltages inside a tv set concern me. Worried about hooking the probe to a live circuit and smoking something... My iso is only good for 1amp anyway. There's nothing "hot ground" on the convergence board. The power board is another story. You may not need the scope on this job, anyway. Good, less to carry to where the set is... I'll poke around those boards looking for questionable solder joints on the connectors. I find it a lot on the arcade boards I tinker with. Since I have blue deflection, I would bet it is the convergence board. The pots also sound like a likely place to look for trouble. Actually, I've never seen a bad pot on these boards. There's no significant current through them, and they don't get turned often enough to wear out the resistance element or wiper. I was thinking about cold solder joints on the pots actually... Found a set at www.servicemanuals.net . The only problem is that the parts all have some manufacturers code on them. Voltages and general information should make it easier to find what I'm looking for. If it's a 12-digit number, like 4835 209 67169, it's probably the Philips part number, and there are plenty of folks on this group who can look it up for you. I think you'll find that the parts in the set have real-world numbers printed on them anyway. Thanks! I'm sure that I'll be back... Thanks a bunch! TV works pretty good, I got it free by simply hauling it off for someone. The internal battery is dead as well. Yeah, it's old enough. Pretty standard lithium coin cell. Not in an easy-to-replace holder, unfortunately. Typical. Which board is it on? Brightness is a bit low. Perhaps it is time to change the fluid. The picture will have a "milky" look due to light diffusion when the fluid is cloudy. Blue tube is always the worst, likes to grow algae encrustation inside. You can tell by looking into the tubes with the front screen off. Dusty lenses and greasy/nicotine filmed mirror can scatter plenty of light, too. Doesn't look milky. Windex to the rescue... They weren't all that bright when new, and considering its age the tube phosphors are probably well burnt. Don't expect it to look as bright as a direct-view CRT. Turning things up will accelerate the phosphor burn and shorten whatever life is left. If you have to tweak the screen, drive, background controls, try to do only enough to get good color tracking. I've never really been around one so this is my first experience. People like to push the brightness and picture all the way up. I don't really notice much of a difference however I understand that it drives the guns harder and wears them out faster. At times, it is difficult to convince people that just because it was free, it doesn't mean that is should be abused. I'll clean up the lenses and mirrors when I'm inside it. Once a crt goes, it probably isn't a viable option to replace, is it? |
#6
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"Ol' Duffer" wrote in message
... In article , says... Thanks a bunch! TV works pretty good, I got it free by simply hauling it off for someone. The internal battery is dead as well. Yeah, it's old enough. Pretty standard lithium coin cell. Not in an easy-to-replace holder, unfortunately. Typical. Which board is it on? IIRC, on a big board in the bottom of the set, near the front edge, under a shield along with the EEPROM. I've never really been around one so this is my first experience. People like to push the brightness and picture all the way up. I don't really notice much of a difference however I understand that it drives the guns harder and wears them out faster. Nitpick: It's not the guns, they are pretty durable, rather the phosphor coating gets the heck burnt out of it. Remember they drive these things so hard they need to cool the faces of the tubes. Right! Electrons are cheap! I could think a little more before simply writing an answer. The coolant is for the destination not the source. At times, it is difficult to convince people that just because it was free, it doesn't mean that is should be abused. I'll clean up the lenses and mirrors when I'm inside it. Once a crt goes, it probably isn't a viable option to replace, is it? It came from a non-smoking environment so it was pretty clean inside. Why don't they make things this easy to get into anymore? Over $400 list, last I looked (each). If they're still available. And lots of time to install, converge, tweak color tracking, etc. And other stuff in the set could go anytime and it's no longer supported by Philips. I'll keep an eye out on the curbs during large item trash pickup for another one... At the price of projection HDTVs, that isn't a viable option. I'd say keep repairs to a minimum, dim the lights a bit, and enjoy it while it lasts. Good advice! I resoldered the square pins and that solved it. Someone had already been into the set. Left a real mess! Looks like they used a torch to solder some new flameproof resistors on. I poked around the blue horizontal area and found a bad solder joint. Looked ok however a little prodding with a plastic probe found it. It is only real dim on shows that have dark scenes. Works great for sporting events which is what I want if for anyway. Picture quality is very good for a set this old. Thanks again! |
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