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Replacing a vintage +8vcc shift register
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gkmaia:
I got a bit of a problem. Got two 74 logic 164 shift registers that are faulty.

The issue is. These registers run on a +8V rail and on the market today I can only find shift registers that will take 5V or 6V VCC.

Has anyone had the same issue replacing these old shifters? Any tip?!





oPossum:
CD4094 / HEF4094 / MC14094
tggzzz:
I assume this is a one-off replacement. You have several options, but none are trivial...

Find a secondhand supplier. There are several such dedicated companies on the web, but they will be expensive.

See if there are 4000 series devices that have suitable timings and pinouts. Pinout could be dealt with using a carrier board.

Use a modern small outline device on carrier board, together with a voltage regulator and level shifters. Be careful of the risetime of a 5V->8V shifter; some can be good up to 5V, and anaemic from 5V to 8V

Timing: most people will verify the tPD and tS timing in their circuit, but tH is equally important and can be less tractable.
gkmaia:

--- Quote from: tggzzz on July 14, 2019, 09:27:46 am ---I assume this is a one-off replacement. You have several options, but none are trivial...

Find a secondhand supplier. There are several such dedicated companies on the web, but they will be expensive.

See if there are 4000 series devices that have suitable timings and pinouts. Pinout could be dealt with using a carrier board.

Use a modern small outline device on carrier board, together with a voltage regulator and level shifters. Be careful of the risetime of a 5V->8V shifter; some can be good up to 5V, and anaemic from 5V to 8V

Timing: most people will verify the tPD and tS timing in their circuit, but tH is equally important and can be less tractable.

--- End quote ---

Yes, I was afraid that was the case. I will get some NOS ones instead of tweaking another one as it is a precision device.

But interesting. Half of the circuit uses 5v logic and other half uses 8v logic. Was that a common thing back in the past? What are the benefits of 8v logic?
tggzzz:

--- Quote from: gkmaia on July 14, 2019, 11:12:45 pm --- What are the benefits of 8v logic?

--- End quote ---

Nothing per se.

There may be advantages in the surrounding circuit, of course.
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