Philips GR2.2 Contrast Dims/Sound Cracks
 

Hi all,

Two days ago I was using my Philips Gr2.2 set to watch some music videos, Normally the picture on this set is fantastic but I noticed an issue that seems to be developing, If the scene changes from a dark scene to an all white scene the contrast dims temporarily and then returns to normal a second later, when this happens the sound also cracks.

One of the videos had camera flashes every few seconds that filled the screen white and after this the contrast got slightly dimmer then returned to normal.

I then noticed that if i turn on teletext and turn it off the same thing happens.

Ive seen on another forum a similar issue present on an L6.1 set.

Where should i start looking to resolve this? Can anyone advise?

Any help appreciated, its not a major issue as normally the picture is excellent but i want to avoid it becoming a bigger issue down the road.

Re: Philips GR2.2 Contrast Dims/Sound Cracks
 

Start with the simple things - check the earthing of the CRT's aquadag.

Re: Philips GR2.2 Contrast Dims/Sound Cracks
 

Good Idea, I was thinking it was somthing to do with the beam current limiter but best to start with the simple stuff, the aquadag earth never even crossed my mind. I'll take a look.

Re: Philips GR2.2 Contrast Dims/Sound Cracks
 

Only had a quick look and i do think its something in the beam current limiter, just by the way its behaving, I let it run and then turned the text on, when text is on the page number gets darker after a minute, then when text is turned off the whole screen goes dull as if the contrast is turned all the way down affects the whole screen including the OSD, then a second later it returns to normal brightness (Does the same in picture mode if rapidly going from a bright to dark image and vice versa so I think (maybe) a bad cap is drifting in value a bit in the BCL. I'll have to have a proper look when ive more time and energy. Pin 15 of IC7309 is the control pin for the BCL so i might temporarily disconnect it and see if it behaves the same way or not to confirm.

Re: Philips GR2.2 Contrast Dims/Sound Cracks
 

Measure the HT line to the line o/p stage, could be very revealing.

Re: Philips GR2.2 Contrast Dims/Sound Cracks
 

HT is at 100.5v

Re: Philips GR2.2 Contrast Dims/Sound Cracks
 

Is it steady from switch on until set is fully warmed up? No fluctuation when fault occurs?

Re: Philips GR2.2 Contrast Dims/Sound Cracks
 

bang steady at 100.5

Re: Philips GR2.2 Contrast Dims/Sound Cracks
 

does anyone have any other suggestions. I temporarily disconnected Pin 15 of the video IC to see if its in the beam limiter and its not, same result. I also changed the Peak drive storage cap and same result. Could it be the video processor itself is failing, its a TDA4680, you guys would know more than me what their reliabilty was like.

or should i be looking somewhere completly different?

Re: Philips GR2.2 Contrast Dims/Sound Cracks
 

Bit late to the party...

I had a GR2.4 that did similar. The picture would dim in steps, and then clear. This set was ex- rental but only 18months old at the time.
The fault was the CRT... I simply lived with it. The set with its gull wing tube gave a great picture. The rest of the family barely noticed it, just me.

If you've got access to a scope, monitor the RGB cathode waveforms, this should show if its the drive that's varying. You can use just a meter, but judgement is more difficult.

In some cases a very gentle tap the the CRT neck can bring the fault on. SJM.

Re: Philips GR2.2 Contrast Dims/Sound Cracks
 

It could be as simple as a dry joint on the LOPT. J.

Re: Philips GR2.2 Contrast Dims/Sound Cracks
 

Even if it's the tube, the drive will probably vary since it uses a closed loop system for cathode bias.

Re: Philips GR2.2 Contrast Dims/Sound Cracks
 

Quick Update, I still havnt solved this but after My IKC2 Ordeal I think it might be an earthing problem, the symptoms are similar, though not the exact same, the picture on the philips wobbles too but only when the volume is pushed way up, the philips is able to go much louder than the Ferguson.

I'll have to go snooping at the board and see if theres any hairline cracks or bad grounds

Re: Philips GR2.2 Contrast Dims/Sound Cracks
 

Hi!

Did you check the 14V supply? As both a part of the video section and the sound module works on this voltage, derived from the LOPT.

Measure the 14V at the CRT panel and at the sound module, are those both steady when the fault occurs? Are the capacitors around the LOPT for the 14V supply good?

Also, a fault on the CRT panel maybe cause a dip in the 14V with can causes the audio crack . .

It also can be a fault in the cut-off circuit (also using the 14V) . .

Re: Philips GR2.2 Contrast Dims/Sound Cracks
 

Hi

I havnt checked the 14v supply yet, just been looking through the manual and the 14v feeds a lot so theres definatly a something in there that could be bad, when I have some spare time I'll get the meter out and test the 14v line and see if i can narrow down the fault. thanks for the tip

Philips GR2.2 Contrast Dim + Sound Crack
 

Hi All,

Now that the 51K5 is sorted and in place of my GR2.2 I have time to go back to this issue with the Philips... The goal is to fix the Philips and put it back into service and retire the 51K5 and put it safely into storage as I want to keep it in working condition and I reckon if i keep it in service it'll fail again and I don't have the mental patience to go routing for more ICC5 faults.

Back to the Philips...So the story is whenever there is an all white or all black image on the screen the contrast dips and once the scene clears the contrast comes back up, for example there's a music video with camera flashes in it and when that scene is playing the contrast dims ever so slightly and the sound cracks...

If i turn on the teletext the contrast goes down and then comes up a second or two later once the teletext is turned off.

The sound only cracks on an all white image.

Someone in the previous thread suggested checking the HT supply and its steady at 100.5v.

It was also suggested to look at the 14v supply as this feeds part of the audio and the video stages and also the cut off.

the 14v supply is coming up at 17.5v without the fault condition and 17.7/17.9 when in the fault condition.

no idea why its high can anyone suggest what might be causing it?

Possibly related when the volume is turned half way up noise can be heard from the speaker, nothing specific just a noise (like air escaping)

Re: Philips GR2.2 Contrast Dim + Sound Crack
 

I think we need to measure starting to check the PSU's

- TDA4680 pin5 (8,5V)
- CRT print C2432 (12V)
- CRT print +190V

Also check C2354, C2365 around TDA4680 and all electrolytic caps on the CRT PCB.

Re: Philips GR2.2 Contrast Dims/Sound Cracks
 

Especially if they're somehow involved in the beam limiter. If all supply voltages are steady during the dip, I would suspect something like that.

Re: Philips GR2.2 Contrast Dims/Sound Cracks
 

Are there any IC holders on any of the plug in modules? I remember a similar fault caused by a holder on an earlier chassis causing problems. We used to remove them and solder the chip directly into the board. Just a thought....

Re: Philips GR2.2 Contrast Dims/Sound Cracks
 

Sorry scrub that... Brain in neutral ! wouldn't cause sound problems...:dunce: