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Project 1969 Philips G22K511 Missing I/F & LOPT, Conversion

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Jayceebee
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I’m just about to leave for work, if the brightness control doesn’t work as you would expect try the lead to the CRT base as it was previously ie before the BL.

John.

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Posted : 14/05/2021 10:47 am
crustytv
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Posted by: @jayceebee

if the brightness control doesn’t work as you would expect try the lead to the CRT base as it was previously ie before the BL

Easier said than done as I have modified my interface board to have the beam limiter components in between the IF pad and the plug post. To get over this I've removed the IF board again and installed an additional plug post, this goes directly to the IF board pad bypassing the beam limiter components. So for testing purposes, I now have two posts for connection to L5121, one with beam limiting, the other without.

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Topic starter Posted : 14/05/2021 11:30 am
crustytv
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After finding HT3 missing from R1081 late last night, I croc clipped in the supply and now HT3 was present. This afternoon I set about installing the missing wire into the harness, a really tricky job with the ridiculous access Philips give on the G6. The supply comes from R1056 buried way down on the PSU tags. I managed to contort myself to get down there and without invoking the dreaded G6 wire-pingitus. Connected the other end of K88 to E88 on the CRT, powered up and still no HT3!!!

Can only be one thing, broken trace, it indeed was. I soldered directly onto R1081. I noticed another trace had a ripple in the copper, however it was not open, even so it may well go that way, so I wire linked it. Furthermore, I cont tested the rest of the traces, all were OK.

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The new 4W brightness pot has arrived, that will now be installed prior to trying to set CRT cut-off.

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Topic starter Posted : 14/05/2021 1:12 pm
crustytv
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Let's hope this 4W is man enough, if not, I'll move the contrast pot to the front, then put the Colvern back in and place it at the back of the set where the contrast came from.

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Now time to try and set CRT cut-off.

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Topic starter Posted : 14/05/2021 1:46 pm
crustytv
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New pot fitted, I have HT3 on R1081, wire disconnected to L1521, raster comes up, not as bright as we've been getting but not dim either. Now over to R7285 CRT cut-off, to adjust for barely visible raster. Ah, now we discover why its one-ended that's as dim as it will go, rotating in the other direction brings the raster up bright. Next thing to look into.

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Topic starter Posted : 14/05/2021 2:17 pm
crustytv
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Found another problem, low anode volts on the PFL200. According to the circuit, it should be 198V. I have 134V when the brightness pot is at one end of its travel and 30V when it's at the other. Looking into possible reasons.

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Topic starter Posted : 14/05/2021 2:46 pm
Cathovisor
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@crustytv

Well, it follows from the readings we were getting on the tube's cathodes. So we need to look at the feed from HT3 to it - a lot of resistors in the way. Is the screen voltage low too?

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Posted : 14/05/2021 3:22 pm
crustytv
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Posted by: @cathovisor

Is the screen voltage low too?

What's really doing my head in is consistently looking at the SS circuit when I should be looking at the DS cct, it'll stop me wondering why nothing tally's. 🙄

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The screen is 264V with the brightness at one end, 203V with it at the other, which I think is about right.

I think I'm going to remove the IF board to check all the suspect components circled in red. Whatever one or more are the cause, the board would have to come out to replace it or them, so I might as well cold check and replace.

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Topic starter Posted : 14/05/2021 4:13 pm
Jayceebee
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What's happening on the cathode of the luma section of the PFL200 and does the preset brightness control work?

John.

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Posted : 14/05/2021 9:45 pm
malcscott
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Hi Chris, i have found Philips G6 w/shop manual if it is of any help to you.

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Posted : 15/05/2021 11:34 am
crustytv
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Some progress has been made, I'll try and explain.

Checking the components in the HT3 feed to the anode of V2001, one of the drop-off pair of resistors was marginally out of tolerance, I replaced the pair regardless. Coil L2701 was spot on at 7.5R as was L2661 at 6R. R2120 10K had gone high to 12.5K so was replaced. C2047 was also found to have been faulty despite previously testing good, I think under loads its died. This was a 12.5uF @ 350V, the nearest I had to that was 22uF 400V or 10uF 400V, the 10uF was installed.

Powered on with the link to L1521 removed, i.e. not connected to the new beam limiter circuit and not connected to the original pad, in other words totally out of circuit.

Observations:

All the popping, farting and disturbances have been eliminated, the scope shows a nice clean trace of the low video, no more horrible spikes.

Looking at the TV screen I thought Oh, oh its blank, no EHT!  Looking at the Brandenburg I could see it was indicating 23kV. Ah-ha now R7285 is doing its job, backing it off from its one-ended state the raster could be seen. Adjusting the brightness pot and that now seems to have a good range too.

Now rotating the new 4W brightness pot, and monitoring pin 9 of the PFL, I have 273V at max, and 220V at min brightness on the screen of V2001. A little high at max brightness but maybe that's down to setting up. The anode volts are max brightness 77V, min brightness 153V.

Adding the wire to L1521 on the interface board, thus employing the new Beam limiter circuit. Monitoring just anode volts on PFL. The raster again is much brighter to start with, tried adjusting R7285, but now you cannot cut the CRT whereas before you could with no wire to L1521. Adjusting brightness to max gives anode volts of 75V, and 156V at minimum, but as I say CRT does not go very dim. Change in brightness on screen is just barely perceptible, whereas with L1521 not supplied brightness operated as one would expect.

Finally, L1521 connected to circuit in original config, bypassing the new beam limiting circuit but connected directly to the IF pad as originally designed.  Anode voltage reads as follows, brightness at max is 97V, and at minimum its 163V. The CRT cut-off R2785, operates, but again you cannot cut-off, even when its one ended.

Conclusion:

R7285 only works to cut of the CRT as it should, when the cable going to L1521 is not connected at all, not to the new beam limiting cct or connected to the original pad. In this state when R7285 is one-ended the CRT is blank, backing off from this state you can raise the raster to be just visible, the brightness control also seems to function much better. Max anode volts are still down from the cct expectation of 198V & screen volts a tad high. All the interference was caused by C2047.

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Topic starter Posted : 15/05/2021 4:09 pm
PYE625 liked
PYE625
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Posted by: @crustytv

All the interference was caused by C2047.

At least that is one headache out of the way 👍

To understand the black art of electronics is to understand witchcraft.
Andrew.

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Posted : 15/05/2021 4:27 pm
Katie Bush
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Good grief, it looks like you've gone a hell of a long way while I've been away from the metaphorical bench - It makes your brain feel like cotton wool, just reading through it.

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Posted : 15/05/2021 4:54 pm
Jayceebee
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Well done on sorting that out. Don’t be worried about not being able to produce a black screen with the brightness at minimum, not all sets did. The reason I say this is I’ve only just noticed the DS CRT base has a switch in the luminance input from the IF to L1521, it does the same role as disconnecting the wire from the new BL. I haven’t checked but I bet that it is to assist in setting the cutoff control.

Just checked and that is what it's there for, redesign of the clamp circuit and brightness control arrangements have made the switch unnecessary on the SS.

John.

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Posted : 15/05/2021 5:07 pm
Katie Bush
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Posted by: @jayceebee

I’ve only just noticed the DS CRT base has a switch in the luminance input from the IF

You're right - It did, and I'd forgotten all about that. The switch sat in that "U" shaped notch at the top of the octagonal board. I think it was omitted because too many heavy handed oiks were breaking the board while pressing on the switch (It was a push button), and even breaking the CRT neck, which happened to me once, on a freshly regunned tube! - Granddad wasn't overly pleased. Thankfully, the regunners were more sympathetic about it and offered a free replacement tube.

Also on the DS CRT base panel there was a small relay and some additional pots which were switched in/out of circuit according to the state of the colour of/off button on the front panel. The relay and pots were to allow for a more realistic B&W picture during B&W broadcasts (Monochrome White Balance) without compromising the colour set up.

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Posted : 15/05/2021 5:21 pm
crustytv
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Posted by: @jayceebee

Well done on sorting that out. Don’t be worried about not being able to produce a black screen with the brightness at minimum, not all sets did. The reason I say this is I’ve only just noticed the DS CRT base has a switch in the luminance input from the IF to L1521, it does the same role as disconnecting the wire from the new BL. I haven’t checked but I bet that it is to assist in setting the cutoff control.

Just checked and that is what it's there for, redesign of the clamp circuit and brightness control arrangements have made the switch unnecessary on the SS.

I could easily fit a 3K A1 switch on the CRT there's mount holes and I test fitted one. However, I won't be doing this because Marion is absolutely correct, applying pressure to the rocker flexes the CRT base way too much for my liking, I'll stick to just pulling the wire from my interface board.

Well, deep joy.....now with a dimmer, blank & snow-less raster, its back to the less than fun problem, the IF fault and why I have low video. Somehow I feel less than enthusiastic about this prospect.

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Topic starter Posted : 15/05/2021 5:43 pm
Jayceebee
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Chris don't get too disheartened, you've come so far with this, monochrome pictures at least can't be too far away. Once you get back into fault finding with the sweep gen I'm sure you'll crack this. What I will say is try using the sweep gen on a working TV with the tuner disconnected and get to know the feel and what to expect from the output of the detector, also what levels you need to feed in at various stages to produce the same level output from the detector.

John.

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Posted : 15/05/2021 6:02 pm
PYE625
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Compare now with day one and tremendous progress has been made.

Lets face it, it was never going to be easy. Sometimes easy is good, but it can be boring though.

To understand the black art of electronics is to understand witchcraft.
Andrew.

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Posted : 15/05/2021 6:08 pm
Jayceebee
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Posted by: @jayceebee

What I will say is try using the sweep gen on a working TV with the tuner disconnected and get to know the feel and what to expect from the output of the detector, also what levels you need to feed in at various stages to produce the same level output from the detector.

I'll rephrase that. To get say 1V output from the detector.

John.

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Posted : 15/05/2021 6:20 pm
crustytv
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Should I be injecting for about 1V pk-pk or over?

IFfreq 1
IFfreq 2

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Topic starter Posted : 15/05/2021 6:42 pm
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