The set has worked quite well since I acquired it August last year. This week it broke down, no sound and vision although the motorised tuner continued to work. An easy fault to find, R159 (1720hms) in the heater chain had gone open circuit. When the set is converted to 625 lines by fitting the new IF amplifier unit and valve UHF tuner R159 is shorted out by connecting a link between tags A1 and A5. In use as a 405 line only receiver the resistor dissipates 15.5 watts! I'm surprised the manufacturer has opted to use a wire ended resistor. Watts = current squared X resistance. To fix the set I found two high wattage resistors, one is 400ohms and the other is 350ohms. Connected in parallel the measured resistance is 178 ohms, that's near enough. In use the resistors sure do get hot.
The 705T Senator is working again but it really needs the alignment attending to. Need a Neosid hexagonal trimming tool to do that. Otherwise it'll be crunched tuning slugs.
Till Eulenspiegel.
If the IF transformer formers are like the ones used in the later 850 series they could have warped locking the cores in place.
Even if you have the correct Neosid trimming tool you could break the cores. I don’t have first hand experience of them, I saw the lads from Granada every week at Tech and we used to chat (moan) about the shortcomings of some sets.
If you don’t have the trimming tool I have these, found at the bottom of my tool box. The plastic holder is s bit grubby but the tools are ok. Different sizes so the may fit the cores in the 705T.
If you want them PM your address and I will post them sometime this week.
Frank
Looking at the back of the tuner and the pegs that went into the channel selector holes. It may be a false memory but did those pegs go brittle and break off. The tuner motor then kept on going round due to the micro switch not being tripped?
Frank
Hi Frank, I can't remember having any problems with the tuning pegs, back in the day as the expression goes. According to the service information channel changing is facilitated by screwing the pegs into the required channel position. The pegs also function as the fine tuning for each preset channel.
In 1960 BRC introduced a 23" HMV consolette model which used as similar motorised tuner mechanism as the 705T. The HMV set also had the extra refinement of having an ultrasonic remote control for channel changing and switching the set to standby. A spare position on the tuner was allocated for the latter function.
I'll send you a PM about the tuning tools.
Till Eulenspiegel.
Not a false memory Frank, that tuner in a slightly different guise and using the PCF805/PC97 valve line up made it into the 900 and 950 series, As you correctly recall when the pegs broke there was nothing to tell the motor to stop turning.
John.
A close up picture of one of the tuning pegs. It can be clearly seen that it is slightly misshapen.
Till Eulenspiegel.
