Monitor screen dark but LED stays green.

[Pimpom]

My 7-year old CRT monitor has developed an intermittent fault.
Sometimes the screen goes black but the power LED remains green
(doesn't turn amber). A sharp rap often restores the display.
When it decides to act up, the LED stays green even when it's
turned on for several minutes while disconnected from the
computer.

I did a lot of repair work on a wide range of electronic products
up to the early nineties, but I'm quite rusty now. I've opened up
the monitor but can't see anything obvious in the way of a dry
solder or loose connector. The tube heater glows all the time.
The signal cable goes first to the tube base PCB and connections
to the main PCB are with two flat cables.

Which signal line does a computer monitor use to detect the
presence of a signal? Where do you think I should start looking?
Thanks in advance for any input.

 

[Smitty Two]

In article <i6g1r0$seo$1@news.albasani.net>,
"Pimpom" <Pimpom@invalid.invalid> wrote:

Where do you think I should start looking?

on craigslist for a free replacement monitor. You can barely give away
CRTs these days.

 

[Pimpom]

Smitty Two wrote:

In article <i6g1r0$seo$1@news.albasani.net>,
"Pimpom" <Pimpom@invalid.invalid> wrote:

Where do you think I should start looking?

on craigslist for a free replacement monitor. You can barely
give away
CRTs these days.

I have several computers with CRT and LCD monitors but I like
this one because it has analog controls for brightness and
contrast.(other controls are digital) - much better than fiddly
menus and preset levels when switching between different
programs. It must be one of the last models with analog controls,
which is why I've hung on to it all these years.

 

On Sat, 11 Sep 2010 19:26:47 +0530, "Pimpom" <Pimpom@invalid.invalid>
wrote:

My 7-year old CRT monitor has developed an intermittent fault.
Sometimes the screen goes black but the power LED remains green
(doesn't turn amber). A sharp rap often restores the display.
When it decides to act up, the LED stays green even when it's
turned on for several minutes while disconnected from the
computer.

I did a lot of repair work on a wide range of electronic products
up to the early nineties, but I'm quite rusty now. I've opened up
the monitor but can't see anything obvious in the way of a dry
solder or loose connector. The tube heater glows all the time.
The signal cable goes first to the tube base PCB and connections
to the main PCB are with two flat cables.

Which signal line does a computer monitor use to detect the
presence of a signal? Where do you think I should start looking?
Thanks in advance for any input.

It probably uses one of the sync lines. An intelligent approach would

be to check resources such as www.elektrotanya.com and
http://english.electronica-pt.com/ to see if you can find a schematic.
Failing there, I would use a lighted magnifier and carefully examine
the circuit boards for cracks, bad solder joints, etc. AFTER reseating
all connectors.

Or you c ould get a rubber mallet to whack the monitor each time it
fails.

PlainBill

 

[Pimpom]

PlainBill47@yawho.com wrote:

On Sat, 11 Sep 2010 19:26:47 +0530, "Pimpom"
Pimpom@invalid.invalid
wrote:

My 7-year old CRT monitor has developed an intermittent fault.
Sometimes the screen goes black but the power LED remains
green
(doesn't turn amber). A sharp rap often restores the display.
When it decides to act up, the LED stays green even when it's
turned on for several minutes while disconnected from the
computer.

I did a lot of repair work on a wide range of electronic
products
up to the early nineties, but I'm quite rusty now. I've opened
up
the monitor but can't see anything obvious in the way of a dry
solder or loose connector. The tube heater glows all the time.
The signal cable goes first to the tube base PCB and
connections
to the main PCB are with two flat cables.

Which signal line does a computer monitor use to detect the
presence of a signal? Where do you think I should start
looking?
Thanks in advance for any input.

It probably uses one of the sync lines.

Thanks.

An intelligent approach would
be to check resources such as www.elektrotanya.com and
http://english.electronica-pt.com/ to see if you can find a
schematic.

I downloaded the service manual (Hungarian, it seems) from
elektrotanya.com after I made my initial post, and another from
electronica-pt.com just now after reading your post. They turned
out to be identical. But my chassis is significantly different
from them although the model number and the FCC ID match.

Failing there, I would use a lighted magnifier and carefully
examine
the circuit boards for cracks, bad solder joints, etc. AFTER
reseating
all connectors.

Already did that. No luck. I have a 16mm film projector lens
which is more powerful and optically better than a magnifying
glass. Seems I'll have to do this the hard way - step by step
analysis. Electronics is both a profession and a hobby with me
and, being my own boss, I can afford the time. Luckily, right now
I don't have any major design project that can't wait for a few
days.

Or you c ould get a rubber mallet to whack the monitor each
time it
fails.

There's always that, of course

 

[Chuck]

On Sat, 11 Sep 2010 19:26:47 +0530, "Pimpom" <Pimpom@invalid.invalid>
wrote:

My 7-year old CRT monitor has developed an intermittent fault.
Sometimes the screen goes black but the power LED remains green
(doesn't turn amber). A sharp rap often restores the display.
When it decides to act up, the LED stays green even when it's
turned on for several minutes while disconnected from the
computer.

I did a lot of repair work on a wide range of electronic products
up to the early nineties, but I'm quite rusty now. I've opened up
the monitor but can't see anything obvious in the way of a dry
solder or loose connector. The tube heater glows all the time.
The signal cable goes first to the tube base PCB and connections
to the main PCB are with two flat cables.

Which signal line does a computer monitor use to detect the
presence of a signal? Where do you think I should start looking?
Thanks in advance for any input.

I would check for solder breaks at the horizontal drive transformer,

the horizonta drive transistor, the horizontal output transistor, the
yoke socket and the H.O. transformer. Chuck