Joe's Broken Golden Arrow

[JosephS]

I bought a broken golden arrow a while ago because it came with all of the original packing, manuals including the ni-cds and original charger.

I put some batteries in it.
It takes 6x AA batteries for the transmitter
4x AA for the car and 1 Tamiya plug 6 cell nicd

The controller is on channel 6 27.255Mhz

As advertised the car does not work, but in an interesting way, The controller powers on. The car will only power on with the 6 cell nicd attached.

I but batteries in it but used my 5 cell Nicd battery that I use for vintage and testing .
The steering works left and right full proportional.
The throttle only works full forward or full reverse and does so in response to the controller. There is no stop. Adjusting the throttle trim gets to where I can make it flip from forward to reverse, I can't coax it to a stop.

Importantly when I turn off the power to the car, the motor continues running in the last direction selected.

Does anyone know if this is an easy fix? Since the servo and radio appear working.

How do I test if a relay is working properly? Is there anything to check before I de-solder them?


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There is a wall of notes below.

I am going to guess that it is the motor driving circuit.

I found this excellent Spanish language website
https://reparar-cochesrc.blogspot.com/p/averias-y-preguntas-frecuentes.html

This page is devoted to older toy grade RC and how each component works. I found this schematic on the page

I was going to guess that the relay was bad, they seems to be working, switching between forward and reverse. So maybe the circuit that drives the relay in having this issue?

The circuit was also shown this way( or this may be from a different board)


the relay is described as

On the electronic plate of the Dictator, the two relays are type H500S03-2-C or MR301-3HS with 3 volt coil and resistance of 25 ohms. The coils are in parallel, so if we measure on the plate it would be about 12.5 ohms. There is a transient suppression diode in parallel with the coils.

I found an image online of a golder arrow receiver board

showing the NEC MR301-3HS relay.

[JosephS]

Tutorial on how to test a relay with a multimeter
https://www.etechnophiles.com/test-relay-with-multimeter/

[Dadio]

I don't know much of these but I fixed one of these type boards for a friend by going over all the solder points on the board with a reflow gun but you could just touch then up with a soldering iron , these old boards were usually pretty robust in the components but suffered from dry solder joints .