Service manual

utput Volt

The output voltage from an

Eprom can be a problem and will often be less than 3.5 volts

when the

Eprom outputs are connected to a PLL. With

PLLs such as PLL02A there is

seldom a problem since it usually runs on a supply of no more than 5.5 volts. Since 3.5

volts is more than half the supply voltage the PLL02A sees a "1". The situation with the

MC145106P is different since this PLL usually runs with a supply of 9 volts and requires a

6 volt input to guarantee a "1". Although the

Eprom manufacturers do not recommend it,

the answer has been found, by experience, to be the addition of pull-up resistors from the

Eprom output pins to the

9 volt supply. Resistors of about 10k in value should be used.

Lower values can cause excess current to flow through the silicon

substrate which will

gradually kill the

Eprom. This method has been in use in hundreds of units for several

years with no problem. If you really want to play safe you could use a couple of 4050 non-

inverting hex buffer ICs or 40109 level shifter ICs.