UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post

Mark1960 · 28th Jun 2021, 11:26 pm

I think parasitic diodes in the output of U1 would still pull the chip select down when 5v is turned off.

R1, R2 and R3 are also probably going to be draining the battery when 5v is off.

I think R1 and R3 could pull up to 5v instead of the battery supply.

You could power U1 from the battery supply and remove R2, but then you probably don’t want to use the spare gate as an inverter for the address buffer enable.

The 74hc02 might not work with address input levels from the SCMP, and might be better to use 74hct02. I wasn’t sure if you deliberately picked the hc or if that was just a package that was available. Then the 74hct02 probably shouldn’t be powered from the battery as it might not behave itself at battery supply voltages.

If you have 74hct4070 instead of the 4070, or 74hct86, you could use the spare gate as an inverter. I don’t think a cd4070 would be fast enough for the address buffer circuit. But this would mean the prbs generator is not completely separate from the rest of the board.

28th Jun 2021, 11:26 pm	#13
Mark1960 Octode Join Date: Mar 2020 Location: Kitchener, Ontario, Canada Posts: 1,294	Re: Ortonview PCB I think parasitic diodes in the output of U1 would still pull the chip select down when 5v is turned off. R1, R2 and R3 are also probably going to be draining the battery when 5v is off. I think R1 and R3 could pull up to 5v instead of the battery supply. You could power U1 from the battery supply and remove R2, but then you probably don’t want to use the spare gate as an inverter for the address buffer enable. The 74hc02 might not work with address input levels from the SCMP, and might be better to use 74hct02. I wasn’t sure if you deliberately picked the hc or if that was just a package that was available. Then the 74hct02 probably shouldn’t be powered from the battery as it might not behave itself at battery supply voltages. If you have 74hct4070 instead of the 4070, or 74hct86, you could use the spare gate as an inverter. I don’t think a cd4070 would be fast enough for the address buffer circuit. But this would mean the prbs generator is not completely separate from the rest of the board.