05-08-2012, 07:38 AM
Unless you wish to keep the circuit original Al, rather than to simply overcome the fault, it might be much easier to use a 74HC390 decade divider IC. They're widely used, cost about 50p, and one IC could be used for n/10 and n/100. You could then abandon the transistorised decade dividers, and take the 1Mhz output and feed it into the IC, with 100kHz out, and couple that to the 'downstream' circuitry. EG:
http://books.google.co.uk/books?id=0g1Mnf5NGUcC&pg=PA168&lpg=PA168&dq=74hc390+decade+divider+circuits&s
The other alternative, given the difficulty of access to the components, would be to replicate the Marconi circuit on stripboard, test it to make sure it functions OK, then add that as a 'fix' between the 1 Mhz output and the rest of the circuit, but it would be more complicated than just using an IC.
As you've already replaced the active components, (transistors, diodes), then logically, it can only be the resistors - perhaps one or another has gone high, dry joints due to age, or open circuits. From what you say, it must be quite hard to even discover where to put a scope probe, or do voltage tests, let alone remove and replace resistors, transistors etc.
It isn't so much that the circuit is complex, as that the mode of construction doesn't lend itself to ease of servicing.
Just a few thoughts.
http://books.google.co.uk/books?id=0g1Mnf5NGUcC&pg=PA168&lpg=PA168&dq=74hc390+decade+divider+circuits&s
The other alternative, given the difficulty of access to the components, would be to replicate the Marconi circuit on stripboard, test it to make sure it functions OK, then add that as a 'fix' between the 1 Mhz output and the rest of the circuit, but it would be more complicated than just using an IC.
As you've already replaced the active components, (transistors, diodes), then logically, it can only be the resistors - perhaps one or another has gone high, dry joints due to age, or open circuits. From what you say, it must be quite hard to even discover where to put a scope probe, or do voltage tests, let alone remove and replace resistors, transistors etc.
It isn't so much that the circuit is complex, as that the mode of construction doesn't lend itself to ease of servicing.
Just a few thoughts.
Regards, David.
BVWS Member.
G-QRP Club Member 1339.
'I'm in my own little world, but I'm happy, and they know me here'
BVWS Member.
G-QRP Club Member 1339.
'I'm in my own little world, but I'm happy, and they know me here'
