Magnavox RH8524 Blue shifted left

[Kirk S.]

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.

 

[Ol' Duffer]

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.

 

[Kirk S.]

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]

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.

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.

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(?)

 

[[email protected]]

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.

 

[Kirk S.]

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.

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.

 

[Ol' Duffer]

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.

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.

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 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.

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.

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.

 

[Kirk S.]

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...

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...

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...

Yeah, it's old enough. Pretty standard lithium coin cell.
Not in an easy-to-replace holder, unfortunately.

Typical. Which board is it on?

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?

 

[Ol' Duffer]

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.

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?

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'd say keep repairs to a minimum, dim the lights a bit,
and enjoy it while it lasts.

 

[Kirk S.]

IIRC, on a big board in the bottom of the set, near the
front edge, under a shield along with the EEPROM.


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.
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!