Service manual

36
µPD 2824 – Ex a mpl e
The uPD2824 is a popular PLL in America but is internally programmed for only forty
channels. The internal "N" codes are 91 to 135 with the usual "hops". Notice that these are
exactly the same "N" codes which were used in the uPD858 rigs but they are accessed,
here , by a channel switch which provides a BCD output of 00 to 39. This is one of the
"impossible" chips and must be replaced if we are to use the rig on the 10 meter band. The
obvious choice is the MC145106P because, not only does it give us the required "N"
codes, but also the essential 5.12 MHz output pin, without which the rig will not work.
Unfortunately it does not have the internal amplifier for PD filtering, consequently we must
add a VMOS Field Effect Transistor to complete the conversion.
The MC145106P can be used to provide the standard FCC channels and the table shows
the codes in their entirety so that you can compare them with the new codes required for the
"Novice" band. The rig MUST NOT be made capable of working on both bands ,
otherwise you are likely to be in breach of the law in most countries.
A provisional PCB layout is given but it must be pointed out that this has not been tested.
You can see from the column marked " Eprom Location" that the Address code is taken
directly from the channel switch which, as mentioned, gives Binary Coded Decimal from
00 to 39. Only six Eprom inputs are required and, for the "Novice" band, only six outputs
are required, although we have used all eight in the actual layout. The three Most
Significant Bits remain the same for all forty channels and will change only if you need to
add more channels in the 10 meter band. If that is the case, you will probably need to alter
our layout to accommodate a transistor inverter and allow access to at least one other Eprom
input pin in order to switch between bands.
Notice how much simpler and cheaper the Eprom method is when compared with the
alternative of changing THREE crystals for every band which you want to add! Even then,
without an Eprom board, you would still be left with the FCC "hops".