I picked up this set (and several others 
) on a recent visit to fellow forum member neil29. It's a Pye model 170 single-standard hybrid mono TV dating from the early 1970s using the Pye 173 chassis. I was originally just going to strip it for parts but it was complete apart from possibly the wrong back cover. It seemed a shame to break it up and I thought it might be worth trying to get working.
Luckily, the VRAT Technical Library had an article about this very set, in the Les Lawry-Johns "Servicing Television Receivers" series, June 1976. I downloaded the article and powered up the set. All the valves lit up except the EHT rectifier DY802 which runs off the line output transformer. I could hear the sound and the frame timebase working, but there was no EHT and no sparks could be drawn off the PL504 and PY800 top caps. Voltage checks showed the HT1 to HT4 rails, the 19v and 11v were all present. Following the article's advice, I unplugged the DY802. Still no sparks could be drawn from the PL504. I tried another tested PL504 and PY800, and an untested PCF802 valve just in case. I noticed the 'new' PL504 was getting a bit hot - still no EHT though.
Voltages on the bases of PCF802, PL504 and PY800 seemed about right, only the PCF802 pentode anode was a bit low at 93v instead of 110v. Screen grid resistor R84 was intact. Still following the LLJ guide, I unplugged the scan coils and linked R84 to pin 2 of the PL504. Again, no joy. Then I had another idea. My digital multimeter can measure frequency. I connected it between pin 2 of line output valve PL504 and ground. When the set warmed up, the meter showed 15.6KHz on the valve's grid, this presumably means the line drive is working.
The only thing left now seems to be the line output transformer itself. If that really is the case, it sadly looks like it's spare parts only unless someone's got a spare LOPT. Is there anything else I can do to prove it's the LOPT that is definitely faulty? The LLJ article comes to that conclusion after the valves and scan couils have been checked.
Any overheating of the pl/py?
have you checked the boost cap?
rob t
have you checked the boost cap?
rob t
+1 ...!
You may be unfortunate enough to have a duff LOPT but there are lots of other components (= fault possibilities) to check out first ...
When all else fails, read the instructions
...and don't forget that when LLJ wrote that article, the set's were not 40 odd years old......! I'd say replace the boost cap at least. If it is the LOPT, it might just be the overwind in which case a solid-state EHT reccy might be a solution.
Rich
When this model was first released we had a few of them go on fire within the few weeks and the black plastic back cover at the top right hand corner above the line output stage melted and fell inside the set. The pcb around the line output valves was completely charred so it was difficult to know what was going off and the sets were a write off.
I soon had one in for repair where the TBA 550Q video chip had failed and after I repaired this I was operating the brightness control up and down when I heard a feint sizzling that varied with my operating the control. Suddenly I could see a small plume of smoke and then flames!
So really I was in the right place at the right time, it was a very strange breakdown of one of the capacitors in the line output stage I don't remember exactly which one now but it was in the pf range.
I replaced it with a red pulse ceramic type and that solved the problem, sorry I can't remember the value but I did get a £25 award from Philips though - I remember that. 
Eddie
I did get a £25 award from Philips though - I remember that.
Eddie
Those were the days! There was a poster in the Philips workshop but I can't remember the wording now. Everyone was encouraged to report any major problems encountered during servicing direct to the factory or to our Trade Support department who would then investigate. If you were really lucky, it would get printed in 'Service Tips' the trade magazine that went out to authorised dealers. That was another £25!
Rich.
Ah when £25 was $50 and not 240 Chinese Yuan. 50 tank fulls of petrol on the scooter (in 10s notes) 
Disconnect the Overwind and remove the DY802. Get a Thorn 1500 triper and connect it in place of the overwind and the tube final anode.
If you get life on the screen, it's the overwind.
Cheers,
Steve P
Thanks for your help so far.I didn't have much time to look at the TV this weekend, but I've checked / substituted capacitors C71A, C72, C72A, C73 (boost cap), C74.
Another thing I noticed: the HT1 voltage (and other voltages derived from it) is lower than it should be (HT1 reads 195v instead of 237v). When I unplugged the scan coils, this disconnects the screen grid resistor to the PL504 and the HT1 voltage goes up much higher, so it seems the line output stage is overloading HT1. After a few minutes with the scan coils plugged back in, the fusible resistor R59 in series with HT1 sprang open.
I disconnected the EHT overwind from the LOPT but didn't add a 1500 tripler, however there was no spark possible from either of the valve top caps so I'm not sure if a tripler would help. There still seems to be an overload somewhere. It's not looking good. Any other ideas?
P.S. service data is in VRAT technical library https://www.radios-tv.co.uk/dmanager for those who have access. (LLJ TV servicing 1976)
Check for any line drive with a scope.
There is another old trick that you can try. Disconnect the DY802 top cap connection and run the set from cold for about 15-20 minutes. Switch off and feel the EHT overwind, if it is warm then you have shorted turns on the EHT overwind, if it is cold then the problem lies elsewhere maybe shorted turns on the main LOPTY windings.
I disconnected the EHT overwind from the LOPT but didn't add a 1500 tripler, however there was no spark possible from either of the valve top caps so I'm not sure if a tripler would help. There still seems to be an overload somewhere. It's not looking good. Any other ideas? )
I think you have to remove the overwind to clear the loading if it is short.
shorted turns will have the same effect as a overloaded secondary winding.
When these sets were still in daily use transformer failure was fairly common ISTR.
hope this helps, cheers, Rich.
