80s Philco-branded Philips 13" - Very dark screen

[YamahaFreak]

Adjusting the color control has no noticeable effect on brightness. I pored over the entire board and could not locate a service switch anywhere, which actually surprised me, given I usually do find one. All other controls work as they should, just...a really dark picture. Menu is fine, as is blue screen brightness while auto channel searching.

EDIT: It's doing something else I hadn't noticed before. Almost like clockwork every 7-8 seconds, the image will get slightly fuzzy (like someone tuning away from the center of the channel on a knob tuner) and then 'snap' back into focus. Weird. I thought maybe it was some outside interference but nothing I can think of is running nearby.

[old_tv_nut]

Something that cycles so slowly is suspiciously like a beat note between vertical rate and the power line. Usually this means a power supply problem.
A schematic sure would help here.

[zeno]

Not sure if its this chassis or an older one. They were had lots of
bad micro IC's. They came with a sheild. The micro was right
under the CRT & the board was cut out for a shield. Seems they
left them out to save $$ & it bit them in the ass.
When they go almost anything can happen including strange charicters
Japanese & other symbols.
You can try different settings for the AFT searching. Norm, CATV, HRC.
ICC SPSL etc.

73 zeno
LFOD !

[JohnCT]

Originally Posted by old_tv_nut

I think the details that do show are too sharp to be chrominance.

That's true, but the chroma seems to be about 90 percent of the available brightness. The color seems normal but there is indeed a little video on the screen.

John

[YamahaFreak]

Not sure if this helps at all, but here is a scan of the circuit diagram that was affixed to the inside of the cabinet.

[jbattles]

Try to turn the sub bright up and see what happens.

[zeno]

Pretty sure this is NOT the chassis with the micro problems.
Control functions are done one of 2 ways.
1) each control ( color, tint, brite etc) goes from the micro to the
jungle IC on separate lines. They will show a changing DC voltage
as you change the setting. The easy & better way IMHO.

2) data & clock lines come into the jungle IC. Its decoded within the
jungle IC. All you can do it watch for activity ( on scope) on the data line when adjusting controls. Bursts of activity may happen even when not changing controls. This is the "modern" way of doing things. Like energy star
better to avoid it at all costs !!

In any case I would say its a video problem for sure. OSD shows
a strong looking CRT & eliminates easy problems. Time to dig in.

enuf fer now
73 Zeno
LFOD !

BTW I probably have the training manual for this set if you go further.....

[vortalexfan]

I think I might have the Magnavox Version of this set if you need some assistance with what things should look like. Mine does work properly and does have its original remote.

[YamahaFreak]

Originally Posted by jbattles

Try to turn the sub bright up and see what happens.

That was one of the first things I tried, right after G2. Barely any difference at all, so I put it back where it was.