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Old 7th Sep 2021, 2:37 pm   #1
xereeto
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Question First repair project - PYE 450 (Philips G11). Weird beam distortion.

Hi folks,

I'm very new to the hobby of vintage electronics repair, coming from a background of simple digital electronics.

I recently acquired a PYE 450 television from circa 1978 (pictured below), which was completely dead when I got it. After reflowing the solder joints on the power supply board, I was able to bring it to life and after a little coaxing I had it producing a decent picture from a VHS input. I thought I was pretty much home free at this point. However, after being turned on and displaying for roughly five minutes, the image started to bow in at the sides. This distortion is now permanent, and I'm not sure how to approach troubleshooting it. The degree of bowing seems to respond to the brightness of the image, with brighter scenes appearing less distorted.

Attached are images of the television, its internals, and what the fault looks like. Here is a video as well, showing the distortion changing with the picture being displayed.

Any advice is greatly appreciated! Thank you.

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Old 7th Sep 2021, 4:56 pm   #2
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Default Re: First repair project - PYE 450 (Philips G11). Weird beam distortion.

In the trade this chassis is known as the Philips G11

I am trying to see if the hum is mains asynchronous, I don't think it is, but your TikTok style video is too short to tell

If you run the set with a stationary picture displayed, does the kink in the sides slowly move up or down or does it remain stationary?
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Old 7th Sep 2021, 5:10 pm   #3
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Default Re: First repair project - PYE 450 (Philips G11). Weird beam distortion.

D4021, a 27V zener diode type BZX79C27 on the PSU panel can cause this problem on the G11 particularly if it is 100Hz ripple (are there 2 moving kinks on each side of the screen?) this is part of the active smoothing circuitry.

If it was fixed distortion (ie. not moving) then the EW circuit has a problem.
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Old 7th Sep 2021, 5:35 pm   #4
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Default Re: First repair project - PYE 450 (Philips G11). Weird beam distortion.

Thanks for the reply! Apologies if this is a double post, but my previous response to this did not appear after I pressed 'Post Quick Reply' and there was no indication that it was waiting for mod approval.

I used a Commodore 64 to provide a stationary image, and this was the result. It appears that the kink remains stationary but there is some ripple along the sides. The distortion has actually gotten a bit worse since I last turned the set on two days ago, with the middle of the image now being rather out of focus. Please let me know if this video is still too short - I'm scared to run the TV for any length of time lest something go pop!

Cheers
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Old 7th Sep 2021, 5:40 pm   #5
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Default Re: First repair project - PYE 450 (Philips G11). Weird beam distortion.

Swing open the right hand part of the chassis and look at the lower panel. This is the power supply. look at the large main smoothing capacitor if it is blue you are fine. If it red do not power the set up until you have replaced it. the Red smoothers were notorious for failing the rivets would arc and cause the HT supply to go through the roof. this caused all sorts of failures including the EHT going sky high and cracking the tube neck.
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Old 7th Sep 2021, 5:45 pm   #6
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Default Re: First repair project - PYE 450 (Philips G11). Weird beam distortion.

Quote:
Originally Posted by slidertogrid View Post
look at the large main smoothing capacitor if it is blue you are fine.
Rich
Fortunately someone already gave me this advice before I turned it on for the first time! The giant capacitor is indeed blue. Attached is a picture of the power board, in case it's of any use!

Regards

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Old 7th Sep 2021, 7:19 pm   #7
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Default Re: First repair project - PYE 450 (Philips G11). Weird beam distortion.

That is 100Hz ripple as has 2 kinks per side, do check the Zener diode I mentioned earlier (preferably by substitution) and the components around it, do you have a circuit diagram btw ?

This set uses active filtering in the PSU where a relatively small value capacitor via transistor action smooths the 100Hz dual Thyristor output, the larger Cap (which is the correct welded light blue type btw) doesn't smooth the main HT line as such rather counterintuitively, and the earlier non-welded types did cause other more serious problems alluded to earlier.

Edit: you are right not to run it for any length of time in that condition as if the active smoothing circuit isn't operating the BU208 Line Output Transistor will fail in a short time.
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Old 7th Sep 2021, 7:52 pm   #8
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Default Re: First repair project - PYE 450 (Philips G11). Weird beam distortion.

Thanks, I'll look into that. I think this is the circuit diagram for my TV?

I guess I'll need to order some parts for this before I can get any further, which is unfortunate. There also must be some other big fault because one thing I forgot to mention is that I had to replace a blown fuse right at the start. Something must be broken to have caused the fuse to blow...

Other than a zener diode, what components would be a good idea to buy so that they are on hand for whatever may crop up in the rest of this repair project? Capacitors, resistors, certain types of transistor?
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Old 7th Sep 2021, 8:25 pm   #9
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Default Re: First repair project - PYE 450 (Philips G11). Weird beam distortion.

Not necessarily, the fuse could have blown on its own on these, or dry joints could have been responsible in any event.

Before you buy anything first prove that the items are actually faulty by testing and voltage measurements.

The Zener diode I mentioned became a stock fault late in the day for these sets and has also caught many an unwary engineer out at least once before.

The first time I had it, it did take some tracing! with many other parts replaced before I realised (finally!) what was wrong.

Obviously make sure the large cap is discharged first! the Thyristors are not easy to check cold (best by substitution) unless S/C of course but rule everything else out first. Check the 4 bridge diodes cold (ie.dead /not powered up) The main HT line on this set is 156 Volts so check that too.
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Old 8th Sep 2021, 9:40 am   #10
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Default Re: First repair project - PYE 450 (Philips G11). Weird beam distortion.

As stated it probably is a power supply fault. It would be worth just checking the outer graphite coating on the CRT is connected. I can't remember how it is done on the G11 sometimes there is a long spring stretched over the coating the clip holding it can break or the wire connecting the spring can become disconnected, the EHT lead is also clipped to the LOPT with a small spring clip this connects to the outer braid of the EHT cable, it is worth checking that is secure as well.
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Old 8th Sep 2021, 8:39 pm   #11
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Default Re: First repair project - PYE 450 (Philips G11). Weird beam distortion.

I always liked the G11 and sold many of them, possibly because I was able to undercut the national dealers.

I did have at least one blue capacitor fail so until you are sure of the fault I would change it. The BANG when the mains rectifiers fail is very loud and as for the tube..............................

After 4 Philips supplied rectifiers failed I used 1N5408 diodes, 1000 v @ 3 A the PCB holes had to be enlarged to fit them. Workshop mains voltage was usually 255 volts.

The E-W coil on one of the top boards could overheat and droop downwards giving very odd pin cushion faults.

They were lighter than a Thorn 3500 or a 2000.

Best wishes,

Geoffrey.
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Old 9th Sep 2021, 10:13 am   #12
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Default Re: First repair project - PYE 450 (Philips G11). Weird beam distortion.

That's an LCR replacement, so do check it has the word 'welded' written on the body since, as Geoffrey says, the early non-welded ones can fail.
Otherwise I've had the transistor on a heatsink on the top left of the power board (BD203?) give this fault, also the zener as R2B suggests. Whatever it is, the fault will be in the active smoothing circuit.
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Old 14th Sep 2021, 1:50 am   #13
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Default Re: First repair project - PYE 450 (Philips G11). Weird beam distortion.

Hi, back again after taking a break for a few days.

I must admit I'm a complete rank amateur here, so this may be a silly question, but where will I find this D4021 diode? On the power board I see nothing labelled '021', and while it is mentioned by name in the text description underneath the schematic I linked here, it doesn't seem to be depicted in the schematic itself.

Thanks
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Old 14th Sep 2021, 1:40 pm   #14
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Default Re: First repair project - PYE 450 (Philips G11). Weird beam distortion.

Aha! Your manual is a pre-production one or at least very early so differs from the production series.
Looking at your board with the infamous capacitor at the top you will see an odd neon-like thing to its left. This is a glow switch. Drop down a little and there should be D21, just to the right of the heatsink, unless you have a very early board - this is for the BY01/02 version.
My notes say to also check R51 (120R), T33 (BCX32), T32 (BD201 on heatsink) and R25 (10R).
Good luck!
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Old 14th Sep 2021, 1:47 pm   #15
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Default Re: First repair project - PYE 450 (Philips G11). Weird beam distortion.

Found it! On the board pictured in your manual, R19 and D21 are soldered in series across the large resistor R30 at the top left of the board. I'd expect your board to be like the one in my manual, however. Looks like a bit of an afterthought, but oddly D21's function is described in your manual's circuit description.
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Old 14th Sep 2021, 1:57 pm   #16
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Default Re: First repair project - PYE 450 (Philips G11). Weird beam distortion.

Here you go
Attached Files
File Type: pdf G11 psu CD.pdf (304.7 KB, 27 views)
File Type: pdf G11 PSU board.pdf (270.6 KB, 24 views)
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Old 15th Sep 2021, 1:01 am   #17
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Default Re: First repair project - PYE 450 (Philips G11). Weird beam distortion.

Thanks, I was able to find and replace the diode... unfortunately, the issue persisted.

I tested the bridge diodes, and they're all fine. I tried to test the high voltage line from the point circled in the attached image to the chassis (I was told this was the way to do it by someone else), but strangely I got no reading so I guess they must have been wrong.

And now I have a much larger problem, it seems - after turning it on again a few times in my tests, the CRT now no longer displays any image at all. I still hear the high pitched 15.6kHz whine when I turn it on, and the light on the channel selector illuminates, but the CRT heater doesn't glow.

Obviously either something I've done has broken the TV further, or repeated power cycling in its faulty state has caused something down the line to give out, but either way I'm now at square -1 and thinking of giving up entirely. This may be beyond my capabilities I fear.

Wish I had better news, but ah well.
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Old 15th Sep 2021, 9:31 am   #18
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Default Re: First repair project - PYE 450 (Philips G11). Weird beam distortion.

Have a prod around the LOPT board -these boards can often benefit from a complete solder removal and re-do, in extreme cases they can develop a hairline crack so have your best glasses on LOL.
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Old 15th Sep 2021, 10:08 am   #19
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Default Re: First repair project - PYE 450 (Philips G11). Weird beam distortion.

There is a CRT heater fuse on the Line output panel I have had it fail for no apparent reason.
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Old 15th Sep 2021, 10:09 am   #20
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Default Re: First repair project - PYE 450 (Philips G11). Weird beam distortion.

If the OP can hear the line whistle I doubt he'll need glasses either!
I'd replace all the components I suggested in post #14 as any of them can cause the bowing. If a bridge rectifier diode is short you'd get a bang.
Regarding your new fault, the fuse FS155 has probably failed (1A,top one) or these's a disconnection on socked 3C (second one down. Also check the earth lead from the CRT base hasn't come adrift.
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