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kengolightly · 26th Feb 2020, 2:03 pm

Have brought my Tandberg td20a out of warm dry storage and after quite a few problems with power supply to the logic board I am now at a standstill. Only record, stop and wind operate and have their led's lit. There are no movements on the meters when in record with a microphone source so unsure if it actually recording. Was recommended to check all the ic's in the logic board and I replaced them all, checked each one as I changed them but did not find any faults. I also obtained a new U3 SN74S471N which I tried and as soon as I powered up the deck it went into fast wind and nothing else. I put the original U3 back in and it reverted to the original condition. After reading the service manual it seems the U3 is the prom which controls all logic operations and may well control signals to the audio board. I am no expert and have a little knowledge of circuits. I have seen that there is a programme for the prom and would like any information as to how I can get this deck up and running. Seems a shame when it is such a good deck, Any help or pointers would be greatly appreciated.

26th Feb 2020, 2:03 pm	#1
kengolightly Diode Join Date: Feb 2020 Location: Leeds, West Yorkshire, UK. Posts: 6	Tandberg TD20A logic problem Have brought my Tandberg td20a out of warm dry storage and after quite a few problems with power supply to the logic board I am now at a standstill. Only record, stop and wind operate and have their led's lit. There are no movements on the meters when in record with a microphone source so unsure if it actually recording. Was recommended to check all the ic's in the logic board and I replaced them all, checked each one as I changed them but did not find any faults. I also obtained a new U3 SN74S471N which I tried and as soon as I powered up the deck it went into fast wind and nothing else. I put the original U3 back in and it reverted to the original condition. After reading the service manual it seems the U3 is the prom which controls all logic operations and may well control signals to the audio board. I am no expert and have a little knowledge of circuits. I have seen that there is a programme for the prom and would like any information as to how I can get this deck up and running. Seems a shame when it is such a good deck, Any help or pointers would be greatly appreciated.