H All. I have the 5500 Mk2 tuner that works perfectly and sounds good, but every "locked" station shows a frequency of +0.05MHz. QUESTION, is this just a case of the frequency counter of the display needing a fine adjustment or does more complex adjustment need to be done? I realise it would benefit from a total accurate realignment, but cannot find anyone in the UK that can do it. If it is just the frequency counter how do I adjust this please? .....Thanks for reading.
There is no adjustment in the service manual for this. These tuners actually lock and measure the local oscillator and assume a 10.7 MHz IF. The IF frequency is fixed by the ceramic filters.
I suspect the 4.5 MHz crystal X501, used by the PLL MCU IC501 has drifted off a little with age (1984 model!). Fixing this is quite involved - buying crystals as specials is not easy these days, so if possible just live with it.
I suspect the 4.5 MHz crystal X501, used by the PLL MCU IC501 has drifted off a little with age (1984 model!). Fixing this is quite involved - buying crystals as specials is not easy these days, so if possible just live with it.
Usually it's just the discriminator alignment that needs a tweak in this situation. Very common. Adjust L204 and L202 as described in the service manual on a real station while tuned to its nominal frequency, that should work just about as well as a signal generator. If in doubt, grab another PLL-synthesized FM receiver of conventional, no-frills construction and tune in its LO signal at tuned frequency + 10.7 MHz for a cross-check.
I have tried a number of PLL-synthesized shortwave portables in my possession, and none have disagreed by more than a few hundred Hz on FM, so actual reference oscillator inaccuracy wouldn't be high on my list of possible causes.
I have tried a number of PLL-synthesized shortwave portables in my possession, and none have disagreed by more than a few hundred Hz on FM, so actual reference oscillator inaccuracy wouldn't be high on my list of possible causes.
