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MC3459P -- What makes a good substitute?

Some repair services suggest using 74LS37's or even 74LS00's to replace the Motorola MC3459 located at U15 on Bally & Stern CPU boards. This is not a good idea as this violates loading of the IC per manufacturer specifications. Overloading can result in intermittent errors and/or shortened component lifespan. Below is a table listing loading for each output pin of U15 plus a comparison of various IC's that people have used to replace the hard to find MC3459. Green values are areas of valid operating load conditions. Yellow values are areas of concern. Pay particular attention to output of gate 4 (shown in red) which is required to sink a minimum of 37.6mA. Only four IC's show themselves as being capable of sinking this 37.6mA: MC3459, 7437, 74S37 and 74F37.

Required Bally High level current loading

Required Bally low level current loading

U15, Gate 1

< 0.080mA

7.4mA

U15, Gate 2

< 0.040mA

5.8mA

U15, Gate 3

0.150mA

7.2mA

U15, Gate 4

< 2.52mA **

37.6mA ***

 

 

 

 

Available High level current per pin

Available Low level current per pin

MC3459

18mA maximum

122mA maximum

7400

0.4mA maximum

16mA maximum

74LS00

0.4mA maximum

8mA maximum

74S00 / 74F00

1mA maximum

20mA maximum

74HCT00

4mA maximum

4mA maximum

7437

1.2mA maximum

48mA maximum

74LS37

1.2mA maximum

24mA maximum

74S37

3mA maximum

60mA maximum

74F37

15mA maximum

64mA maximum


Notes:
Current values supplied by actual manufacturer datasheets.
Operating voltages based on manufacturer specified values.
Low level voltage based on (VSS + 0.8) or 0.8 volts (maximum).
High level voltage based on VSS + 2.0) or 2.0 volts (minimum).
** Most IOH of gate 4 is provided by R137 (provides upto 20mA source current).
*** Most IOL of gate 4 is created by R137 (adds 28mA load current).

Conclusion:
Although some repair technicians suggest using a 74LS37 or one of the other 'red' components listed above are valid, this may result in intermittent operation or shortened lifespan. For best results - use only these parts as valid replacements: MC3459, 7437, 74S37 and 74F37.
And remember - "it always works for me" is not justification for a part that is an invalid substitute!