1987 Gaugemaster 2 track controller - track 2 stuck full-on

I suspsect you have a duff output transistor on the output stage or somewhere earlier. The main transistor is the black thing screwed to a largish peice of aluminium. If you look at the number on the transistor then you may be able to fuind a replacement in the Maplin catalogue or online at

It may also the pot on the front panel with the knob on it.

Sorry to sound as though i'm teaching a granny to suck eggs but I don't know how much you know, if you know what I mean...

Cheers,

Rob

James B wrote:

"James B" wrote

Gaugemaster controllers allegedly have a life-time guarantee, so if you're at all dubious about opening the box and trying to fix it yourself then send it back to the manufacturer for free repair.

If you want to query with the manufacturer email them direct at snipped-for-privacy@nospamatgaugemaster.co.uk (removing 'nospamat') for their advice.

John.

I had the exact same problem with an American-made MRC dual controller. I tracked it to the transistor with a voltmeter. Replacing it for ~£2 solved the problem.

I don't know the precise circuit of this controller but assuming you don't mean the speed control knob is mechanically jammed at full, you have a 99% chance that the output transistor has failed. The 1% chance is that some component driving the output transistor has failed. A new transistor will cost you under 5 pounds.

Regards, Greg.P. NZ

Thanks for all your suggestions - I really appreciate your help. I will investigate a factory return, if the lifetime warranty is correct, but I drilled a pop rivet on one bottom case corner years ago to get it open, so they may not like me for that. It's not the potentiometer stuck full-on, and the variable resistance of it is still fine (linear 2k). I am inclined to go for the output transistor (99% chance as Greg said), but I initially hesitated to rip it apart further as they are under the PCB using the bottom of the steel case as a heatsink. I will give it a once-over with a voltmeter before I start. Maplin here I come!

James B

I'm no electronics expert, but I think there might be a clue in your message when you said that the LED display showed full when you switched on the mains power. I was advised to make sure that all output settings were set to zero before powering up to avoid a surge current damaging the output trannies (which aren't so rugged as they're claimed to be.) If you had a short somewhere on your layout at the time, the likelihood of damage would be increased. If you are still getting an output from the suspect channel, there is a possibility that the circuit controlling the pulse width (speed) is damaged, in which case seek expert help. Regards

I think the Gaugemaster controllers output pure DC not pulse-mod (unless you are talking about something which goes on before the output stage).

Adrian