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ronbryan · 15th Apr 2019, 2:46 pm

A lot of the logic in the TF2171 is the obsolete, late 1960's, power hungry 74H series, so I expect that the 5.25V specified at the power supply pins was to allow a bit of volt-drop in the interconnecting wires and the pcb traces. I think that 74H was designed for 4.75V to 5.25V at the chip itself. In addition to the 74H TTL, the Plessey ECL pre-scaler chips run very hot and are powered from the 5.25V supply, so may benefit from a bit less dissipation. You could always check to see if the pre-scaler drive amplitude is adjusted correctly (R19)

Ron

15th Apr 2019, 2:46 pm	#9
ronbryan Octode Join Date: Jan 2003 Location: Guildford, Surrey, UK. Posts: 1,960	Re: Marconi TF2171 Possible Problem? A lot of the logic in the TF2171 is the obsolete, late 1960's, power hungry 74H series, so I expect that the 5.25V specified at the power supply pins was to allow a bit of volt-drop in the interconnecting wires and the pcb traces. I think that 74H was designed for 4.75V to 5.25V at the chip itself. In addition to the 74H TTL, the Plessey ECL pre-scaler chips run very hot and are powered from the 5.25V supply, so may benefit from a bit less dissipation. You could always check to see if the pre-scaler drive amplitude is adjusted correctly (R19) Ron Last edited by ronbryan; 15th Apr 2019 at 2:55 pm.