UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Philips T-Vette

TNC · 3rd May 2007, 12:43 pm

I must say, as someone who is more familiar with valve technology, the world of transistors seems much more difficult - esp. wrt diagnosis.
The TV-ette is also suffering with a power fault. After approx. 5 mins. running, the HT1 volts fall away - first to around 9.5v and thereafter to about 3-4v. The entire process takes about 30 seconds.
I have checked voltages in to T1513 from the rectifier - around 12.5v, and out from T1513 via R4049 to its connection with T4012 where it is 14.75v (on UHF setting) - about .25v too low.
When the voltage starts to fall, the input to T1513 varies between 13v and 12v - but settles to a fluctuating 13v (+/- .5v)(by that time the screen is completely dead) and the voltage going into T4012 similarly varies but again settles at about 13v.
I have looked at the input voltage to the zenner X4006 and that is very steady at 1.77 until the problem begins - it then falls away to .5v.
I have noticed that the problem is initiated ("announced") with a very slight very high-pitched oscillation - something like linebase but hardly audible...but clearly something is suffering!
Turning off for 2/3 minutes seems to reset the circuit but its probably quicker to the collapse - say 2/3 minutes...so heat may be an issue? Is it safe to cold-spray some components in that area?
My logic (probably flawed) tells me that if the voltages around T1513 and T4012 stay above 11ish then presumably the problem lies further in-perhaps with T4014 or X4006. It seems difficult to pin it down exactly and I so I am daunted at the thought of changing a stack of components, all but one of which will be fine!!
Grateful for any thoughts on how I might diagnose more exactly?

Trevor.

3rd May 2007, 12:43 pm	#28
TNC Hexode Join Date: Apr 2003 Location: Westcliff-on-Sea, Essex, UK. Posts: 386	Re: Philips T-Vette I must say, as someone who is more familiar with valve technology, the world of transistors seems much more difficult - esp. wrt diagnosis. The TV-ette is also suffering with a power fault. After approx. 5 mins. running, the HT1 volts fall away - first to around 9.5v and thereafter to about 3-4v. The entire process takes about 30 seconds. I have checked voltages in to T1513 from the rectifier - around 12.5v, and out from T1513 via R4049 to its connection with T4012 where it is 14.75v (on UHF setting) - about .25v too low. When the voltage starts to fall, the input to T1513 varies between 13v and 12v - but settles to a fluctuating 13v (+/- .5v)(by that time the screen is completely dead) and the voltage going into T4012 similarly varies but again settles at about 13v. I have looked at the input voltage to the zenner X4006 and that is very steady at 1.77 until the problem begins - it then falls away to .5v. I have noticed that the problem is initiated ("announced") with a very slight very high-pitched oscillation - something like linebase but hardly audible...but clearly something is suffering! Turning off for 2/3 minutes seems to reset the circuit but its probably quicker to the collapse - say 2/3 minutes...so heat may be an issue? Is it safe to cold-spray some components in that area? My logic (probably flawed) tells me that if the voltages around T1513 and T4012 stay above 11ish then presumably the problem lies further in-perhaps with T4014 or X4006. It seems difficult to pin it down exactly and I so I am daunted at the thought of changing a stack of components, all but one of which will be fine!! Grateful for any thoughts on how I might diagnose more exactly? Trevor.