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SArc air one lane "shorting"

I'm in the us.

Testing now.

Posted another picture, waiting...

@Dr_C

OK, I suggest the following next steps...

 

1/ please visually inspect the area where you removed the flek... is there any chance the copper track is visibly bridging between pin 3 and pin 4? Another photo would help ifpossible please?

 

2/ with the 15V power supply completed disconnected, and with the four pin track power plug also removed please take five measurements with the meter set to the lowest resistance measurement setting. Please measure resistance between pins 1 and 2 - then again with the probes reversed. The please measure resistance between pins 4 and 3 - then again with the probe pins reversed. Finally measure the resistance of the probe leads by touching the two probe tips together directly.

 

This data should help with final pin-pointing ofthe problem...

 

I still suspect the site of the flek of debris I am sure together we can get this powerbase back into full working order... which continent do you live in?

 

C

Ok, on the bad side. That the side closest to Q3, where I think I might see some heat distortion on the back side (pic coming)

I get a slow drop from 1 ohm to .6 regardless of which lead is on either pin.

On the good side, I get no resistance from pin to pin in either direction of lead placement.

 

Lead to lead I get .4 ohms. My meter (I'm using a cheap one because my good one is in my car, but it is functional) is set at the lowest setting of 200ohms.

Dr_C

296 posts

So we are looking at the possibility of a short somewhere between the pcb copper tracks or a failed Q3. This is the transistor which applies the brake function to one of the lanes when activated, i.e. when its gate electrode is driven positive by a signal from the main microcontroller. The transistor should normally be open circuit. This is a surface mount transistor so a little bit of a challenge to remove. Lets look at the photographs before considering next steps. How are your soldering skills and/or dremel skills?

 

C

@Dr_C

So we are looking at the possibility of a short somewhere between the pcb copper tracks or a failed Q3. This is the transistor which applies the brake function to one of the lanes when activated, i.e. when its gate electrode is driven positive by a signal from the main microcontroller. The transistor should normally be open circuit. This is a surface mount transistor so a little bit of a challenge to remove. Lets look at the photographs before considering next steps. How are your soldering skills and/or dremel skills?

 

C

Were it soldering wiring, I'd be good, but never done anything on a board. I think that might be beyond me. But I may know someone.

@Dr_C

Just to add clarity... the flek of debris is located precisely where, if the solder mask was missing... an electrical short would result between ground and the PWM track output.  This would lead to a current overload whenever the corresponding throttle controller is pressed... sound familar?

 

C

If you look to the right of the pointer I think I see some discoloration that might be overheating? It's like a faint white corner like originating at a solder point that is Q3. It is on the side of the connector that's the problem, but I do not know if it is directly connected.

Dr_C

296 posts

Hi MichaelDrago,

What you have found may be significant... perhaps along the lines of a defect during manufacturing whereby the copper material has not been fully etched away between the tracks on the circuit board. Given these narrow tracks connect with the gate drive of the power MOSFETs... might be the problem... please leave as is for the present and I will get back to you with a test procedure to establish if these are indeed short circuits between the copper tracks... looks promising progress...

 

C

 

Dr_C

296 posts

Hi MichaelDrago,

I am sorry to report it does seem likely that the brake transistor Q1 or Q3 is damaged and giving a short circuit... which has the effect of holding the brake in the on condition. There is a small chance there is a short circuit elsewhere on the copper tracks but we cant see anything in a position that would cause this type of short circuit. The earlier identified curved marking,.. if it was a short between tracks would have the effect of presenting the brake from turning on... so cant be the problem.

The challenge in replacing Q1or Q3 is that they are surface mount conponents so quite difficult to handle. I could take a look at it for you... but the postage costs times 2 between uk and usa would I think exceed the value of the powerbase. I wonder if Scalextric customer service might be able to help with a replacement?

 

C

Thank you fur all if your help.

I took it to someone I knew that works repairing circuit boards and he came to the she conclusion.

I'm using it with another power base.

 

Its the best it's good for.

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