Philips G11 G22C706/01 restoration

[RT 1006]

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.

[Red to black]

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

[RT 1006]

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?

[Red to black]

yes, the only difference was some of the AQ which was the equivalent of the 'A' suffixed parts

[Welsh Anorak]

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.

[Sideband]

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!

[Red to black]

Originally Posted by Sideband

..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

[Welsh Anorak]

Yes - and there's a 5W wirewound in the active smoothing circuit that fails with the same effect.

[RT 1006]

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.

[RT 1006]

An update on progress on this set so far, or more accurately, lack of it!

I took the PSU board out of the set a few weeks ago and ran it up on the bench with a 60w dummy load. The output pulsed on and off commensurate with what was seen when it was fitted in the set. Not sure why my initial stand alone dummy load check gave no output. Anyway, there's obviously something within the power supply breaking down under load so next stage is to get the scope out and monitor some wave forms in accordance with the service manual.
Hopefully get some time within the next couple of weeks to get back onto this and will post up a progress report in due course.
Kevin.

[Philips210]

Kevin, it might be worth checking R4059 (15k 9W) on the power supply board. It can often become dry jointed resulting in HT fluctuations. There have been cases of it going o/c as well. There were several references to problems with R4059 in Television magazine.

Regards,
Symon

[RT 1006]

Another update on this set.

Managed to spend a bit of time on it over the weekend. Thank you Philips210 for your suggestion above regarding R4059. I replaced this resistor but unfortunately the symptoms remained the same so I did some waveform checks in accordance with the service manual. These checks highlighted a potential faulty transistor on the PSU board. I've ordered a replacement and just waiting for it to arrive. Once I've fitted it and hopefully fault cleared I'll post up a more detailed report.

The 470uF smoothing cap is a blue one dated 28/84 so obviously fitted early on in the set's life. I've read in a couple of places that even some of the early blue caps can still be troublesome. Can anyone confirm if this is the case or not? I've added a couple of pics of the capacitor below.

Will update again soon.

[Nickthedentist]

I think the word "welded" is relevant, and means it's one of the revised ones without riveted connections to go intermittent and arcy.

Presumably fitted when the set was still newish as a preventative measure (riveted connections led to spikes in the HT and EHT which blew a pinhole in the CRT's neck, allowing its vacuum to be lost and sometimes writing-off an otherwise-ok set).

It's still 40 years old though, so it wouldn't harm to tack something similar in its place, just to prove it's not responsible for your fault.

[greg_simons]

Originally Posted by Nickthedentist

I think the word "welded" is relevant, and means it's one of the revised ones without riveted connections to go intermittent and arcy.

Presumably fitted when the set was still newish as a preventative measure (riveted connections led to spikes in the HT and EHT which blew a pinhole in the CRT's neck, allowing its vacuum to be lost and sometimes writing-off an otherwise-ok set).

It's still 40 years old though, so it wouldn't harm to tack something similar in its place, just to prove it's not responsible for your fault.

Correct, that's a modified capacitor and should be ok provided it's not deteriorated in other ways, the resulting eht spike from an intermittent component used to neatly decapitate the electron gun from the rest of the crt, done more than a few of them!.
Greg.

[RT 1006]

I know I haven't posted anything on this set for a while, unfortunately with various other summer activities going on the telly has been pushed to the side for the time being. I will return to it later in the year and get it up and running as I know how annoying it is when people start a restoration thread but never see it through to a conclusion.

[George Cooper]

I have a new unused TDA2591 in my box of bits if you want it.