Using 5 NAND Gates to prove that there is a hardware problem was very useful, but for a production run using a single chip to replace these is the next step.
...
| Part No | Chip | Manufacture | Speed nS | Package | Price | |||
|---|---|---|---|---|---|---|---|---|
| Min | Typ | Max | ||||||
| 1741279 | SN74LVC1G139DCTR | Ti | <2.5 | SM8 | $ 0.69 | |||
| SN74LVC1G139DCUT | Ti / Farnell | <2.5 | VSSOP | £0.404 | ||||
...
Signals not the same abbreviations as the circuit
The names of the signals on the scope are not all the same as shown in the circuit.
| A19 | A19 | A19 |
| /CE1 | _CE1 | /CE1 |
| /CE0 | _CE | /CE0 |
Printed Circuit Board
2-to-4 Line Decoder
Main points
- Small holes 0.47 mm are drilled in the centre of the pads of H1,so that wire links may be used to connect the signals from the 512K/512K card to the PCB.
- The pads of the footprint of the SOT-23-5 have been made longer, to enable easier soldering of the small parts.
- The bottom Left Hand corner of the PCB matches the shape of the 512K/512K Card for easy alignment.
Provisional Layout
...
Final Layout?
Layout with SO 16 overlaid showing that the holes line up with pads
Layout over the original PCB
The 7 layers
Here are the layers printed on A4 sheets. The board is small, zooming in is generally helpful.
| View file | ||
|---|---|---|
|
|