Don't know how many folks out there will still tackle rehabilitating a 23-channel Tram D201, but here's a common fault that causes the receiver to have "almost" the proper receiver sensitivity. This radio needed about 4 microVolts to hear what should normally require one or less. If the customer had a routinely-high noise level he might never have known the difference. But I do.
Oops. First clue is that T300, the first tuned circuit fed from the antenna socket showed a peak with the slug dead center inside the winding. This is the maximum-inductance position of the tuning slug. Tends to indicate that the winding in question has lost some of its inductance.
This is a fairly-common sort of fault to encounter. The radio was left connected to the antenna during a storm. A nearby lightning stroke didn't hit the antenna, but still generated a surge voltage. Kinda like if someone with a 100,000 Watt linear keys up in your driveway. A strike to a tree three houses down the street can do this. The equivalent RF wattage in a lightning stroke is more than you might think.
A closer view of the surge damage to the input winding.
This is the same part that serves as the input to the noise blanker circuit. Odds are that a radio that needs one of these to restore receiver sensitivity will also need one to fix the noise blanker. And the MC1350 blanker chip usually doesn't survive this, either. Learned to keep that one on hand decades ago.
A new A101-16 coil restored the receiver sensitivity. And the blanker needed both one of these and the MC1350 chip.
Someone ahead of me had already replaced the RF Gain control. It's wired as an attenuator between the antenna socket and the receiver input. Took the same hit as the other parts.
All's well that ends well. Just another reason to unplug or unswitch the antenna from the radio when it's not in use. You never know when a pop-up thundershower will just randomly appear.
73
Oops. First clue is that T300, the first tuned circuit fed from the antenna socket showed a peak with the slug dead center inside the winding. This is the maximum-inductance position of the tuning slug. Tends to indicate that the winding in question has lost some of its inductance.
This is a fairly-common sort of fault to encounter. The radio was left connected to the antenna during a storm. A nearby lightning stroke didn't hit the antenna, but still generated a surge voltage. Kinda like if someone with a 100,000 Watt linear keys up in your driveway. A strike to a tree three houses down the street can do this. The equivalent RF wattage in a lightning stroke is more than you might think.
A closer view of the surge damage to the input winding.
This is the same part that serves as the input to the noise blanker circuit. Odds are that a radio that needs one of these to restore receiver sensitivity will also need one to fix the noise blanker. And the MC1350 blanker chip usually doesn't survive this, either. Learned to keep that one on hand decades ago.
A new A101-16 coil restored the receiver sensitivity. And the blanker needed both one of these and the MC1350 chip.
Someone ahead of me had already replaced the RF Gain control. It's wired as an attenuator between the antenna socket and the receiver input. Took the same hit as the other parts.
All's well that ends well. Just another reason to unplug or unswitch the antenna from the radio when it's not in use. You never know when a pop-up thundershower will just randomly appear.
73
