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Old 17th Mar 2024, 2:03 pm   #1
RT 1006
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Default Philips G11 G22C706/01 restoration

Recently acquired this 22" teletext set complete with its original remote control and trolley stand. It is dated 12 January 1981 so quite a late model as I think they were replaced by the K30 later that year?

I've always liked these 1970's wooden case Philips sets as they remind me of my days as a boy when I used to pull them out of the local rubbish tip and strip them for parts for other things.

This one came to me in non working condition. The set was dead with the fuse on the mains input panel blown. The fuse was replaced and some pre power up checks conducted. The line output transistor measured dead short collector/emitter. Strangely when I loosened the screws securing the transistor to the heatsink the short cleared. A very close inspection revealed a tiny slither of aluminium swarf had been clamped between the transistor case and the mica insulator. Over many cold/hot cycles the swarf has obviously made its way through the mica to cause a short between the transistor case and the heatsink i.e collector/emitter. With replacement mica washer and original transistor back in place I powered the set up via isolated supply with ammeter to monitor mains current voltmeter to monitor HT supply.

I now have what is best described as a pulsing picture with HT appearing to pulse around 135v, mains current sits around 700mA then will jump to around 1.8A after about 30 seconds, sometimes sooner, the pulsing picture remains unchanged.

To try and confirm correct operation of the PSU I tried dummy loading the HT with 60w bulb but this didn't work. The bulb lit for a split second then the psu shut down, I suspect this is because it's not receiving feedback from the beam limiter circuit.

By process of elimination I have confirmed correct operation of the psu by removing HT supply (plug 2C) to the timebase panel and thus line drive to the line o/p panel, with this done HT sits at the correct 157v. If I reconnect plug 2C and disconnect line drive (plug 2F) to line o/p panel (thus taking line scan out of the equasion) HT falls back to 135v. This points to a fault on the timebase panel which I have more or less got down to the line oscillator, IC2510 (TDA2591Q). A number of fault reports I've read also suggest that this IC has been responsible for similar symptoms to those seen here.

I'm now on the hunt for a replacement TDA 2591Q. The one fitted in the set has a QIL - quadrature in line package (offset pins) as opposed to a DIL - dual in line package with in line pins. My question is, does the 'Q' in TDA 2591Q purely to indicate it's a QIL package meaning it could be replaced with a TDA 2591 with suitable QIL to DIL chip holder of which I have a few? Or is the Q just coincidence and bares no relation to package style?

The reason I ask is that the TDA 2591 seems to be fairly readily available but the 2591Q isn't. Hoping that someone with better knowledge of these things than me will be able to confirm either way as extensive research on the net hasn't come up with a definitive answer.

How I wish I'd kept a few of those panels I pulled from all those G8's and G11's I pulled out of the dump but I didn't think I'd be repairing any over 40 years later!

Any information gratefully received, thanks in advance, Kevin.
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Old 17th Mar 2024, 2:10 pm   #2
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Default Re: Philips G11 G22C706/01 restoration

The PSU panel on the G11 should run standalone on a dummy load (60W lamp), there is no feedback as such. It is how we repaired them on the bench back in the day.

edit: it was possible to quil or dil the legs of those ICs back then whichever way you needed to go
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Last edited by Red to black; 17th Mar 2024 at 2:25 pm. Reason: additions
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Old 17th Mar 2024, 2:53 pm   #3
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Default Re: Philips G11 G22C706/01 restoration

Thank you for that information Red to black. I think I'll dummy load the PSU again just to make sure I'm not heading off in the wrong direction.

When you say it's possible to quil or dil the legs do you mean a 2591 is the same as a 2591Q?
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Old 17th Mar 2024, 3:04 pm   #4
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Default Re: Philips G11 G22C706/01 restoration

yes, the only difference was some of the AQ which was the equivalent of the 'A' suffixed parts
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Old 17th Mar 2024, 3:46 pm   #5
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Default Re: Philips G11 G22C706/01 restoration

Yes, the Q simply denoted the quil package. As long as you get a 2591 (not a 2591A) then a DIL to QUIL socket will help.

I'll have a look tomorrow in case I still have one, but it's doubtful.

Nice set by the way with the soft touch buttons rather than the basic fall-apart click switches.
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Old 17th Mar 2024, 4:48 pm   #6
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Default Re: Philips G11 G22C706/01 restoration

Check the glow switch on the power supply. I've had the odd one fail (striking at a lower voltage). Not quite sure what happens to them since they normally just sit there doing nothing until the HT rises above about 165V (I think) when they flash over and pop the mains fuse. It's 40 years since I worked on one of these.....I seem to recall that there was a diode on the PSU panel that would cause a pulsing picture if it went leaky. Something to do with the beam limiting......it WAS a long time ago.....!

Don't forget to check the big 470uF and make sure it's an approved type with rivetted tags. The old type could cause the EHT to skyrocket and blow a hole in the CRT neck....!

I recently passed on a complete set of G11 panels to another collector....sorry!
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Old 17th Mar 2024, 5:47 pm   #7
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Default Re: Philips G11 G22C706/01 restoration

Quote:
Originally Posted by Sideband View Post
..I seem to recall that there was a diode on the PSU panel that would cause a pulsing picture if it went leaky. Something to do with the beam limiting......it WAS a long time ago.....!
Yep a 27V leaky Zener caused strange ripples and hum bars/EW type fault. plus a pair of transistors did cause problems in the beam limiting part of the psu. I could look up the location numbers if required
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Old 18th Mar 2024, 10:44 am   #8
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Default Re: Philips G11 G22C706/01 restoration

Yes - and there's a 5W wirewound in the active smoothing circuit that fails with the same effect.
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Old 18th Mar 2024, 11:33 pm   #9
RT 1006
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Default Re: Philips G11 G22C706/01 restoration

Thank you to everyone for your replies and suggestions. I'm hoping to get some time through the week to get back to the set and will update with progress accordingly.
Kevin.
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