Technical, Techniques, Hints, and Tips > Radio Equipment
Digifleet FM Tx service manual
scimitarjohn:
--- Quote from: HMS Invisible on November 11, 2024, 02:15:41 pm ---I have never seen a Fleet AM set and I can't remember if the NE5044 is a fixed frame time.
There is no rule stating frame length. It can be ~15msec or less for old sets with few channels. Old sets could centre the channel pulses on 1.3ms then +/- whatever.
If you had your old Tx to hand you can pick up its timing in a second by wrapping a few turns round the aerial and crank up the scope gain.
--- End quote ---
Great idea thanks, the bad news, the PCB was so heavily corroded I've had to use a brass brush to follow tracks (death or glory) and seems the coin fell on death, no pulse train from the encoder. The pulse output was iffy anyway, I think a lost cause.
HMS Invisible:
I think a short between tracks on 10 and 11 would make the output a sawtooth.
If it was me, I'd take the chip out it's socket, home in on 10,11 tracks @ experiment on test boards with super crack ultra and Rust-Go. This aerosol from euro car parts opens rusted nuts where WD40 is a penetrative lubricant only.
Rust-Go is a chelating agent dip like USA's Evaporust. It eats oxide in minutes where white wine vinegar converts red rust to magnetite over a day or more. Unfiltered, possibly useless, info from an internet search suggests bicarb & toothbrush.
The cost of either product I mentioned is not justified by long-shot attempt unless you service 2nd hand bikes too.
.
scimitarjohn:
I've checked at the encoder leg and the board, the encoder appears dead. Come to the conclusion that as the pcb is so badly corroded I'd never want to trust in the TX anyway so decided to bale out. I have an alternative route in mind to save the old Fleet mechanicals, if I can make it work I'll let you know. Many thanks for your help, been most interesting and informative. Regards John
HMS Invisible:
If you go back to it one day , serial out is open collector. A pull up resistor connecting to pin 16 (Vcc) takes it high.
It is possible to damage one i/o of a chip but I think, on probability, a fault is elsewhere unless it's been subjected to reverse polarity, in which case, other outputs like pin 15 (Vreg) and Vc mux would not reflect the datasheet traces.
NE5044 is programmable in that it limits number of channels to <7 if an input channel's voltage is set below that of pin 12(range.) So if a pot is turned, or moisture on the board, takes pin 12 high the output pulses stop.
scimitarjohn:
Thought this might be of interest to you, it's from the service manual that came with the AM set.
Regards John
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