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An now for something completely different ...... a pile amounting to 1692* silicon diodes. All of them are still fully functional.

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These have been replaced by fast action Schottky ones on various Scalextric chips over the years ....

Tire Wheel Automotive tire Vehicle Motor vehicle


A mini shell gives an idea of the volume of this pile ....

Tire Vehicle Wheel Automotive tire Toy


Spread out, they cover quite an area.

* 1692 / 4 = 423 uprated chips ....
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What a day ....... another first for me ...
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A member recently returned a non-running chip to me for fixing, one that I had previously fixed before. So what you may ask .... well this is the first one to come back with the same problem as it had in the first place ... it was no longer working after nearly 6½ years of hard use (17th April, 2013).

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The first thing I did was to place it on my test rig.

The motor should run for a very brief moment when it is first powered up, unless the chip has been reflashed with InCar-Pro. This is a good indication because if it does run then the severity of the damage is usually not too bad. The next test is to see if the infrared LED will activate a lane changer. Failing this test indicates major problems with the µ-processor.

Testing revealed that the motor did not twitch but the LED did work.

Next up for attention was the two MOSFETs that I had replaced previously. They checked out as working as specified.

Then my suspicions were turned to the two transistors next to the MOSFETs. Bingo! ...... the one labelled as TR3 was faulty.

Passive circuit component Circuit component Hardware programmer Microcontroller Computer hardware


Both TR3 and TR4 were replaced with new transistors as a matter of course.

There we have it two - happy bananas ......
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No happy bananas with this one .......

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The Drive & Brake MOSFETs have taken a mighty hammering ....

Passive circuit component Circuit component Hardware programmer Microcontroller Electronic engineering


Once it was cleaned up, it was obvious that most of the copper tracks and pads that hold the bits down had long gone ....

Sometimes, it is still possible to repair these severely damaged chips but everything is hanging on by such a thin thread that it really isn't worth the time and effort.
 

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As they say miracles take long .... Theoretically if someone used it as a pace car with a train set where no racing and no massive power draw was used it would be OK but those are a lot of "ifs".

Still, this is the first chip I have seen since watching this thread (nearly 2 years) you haven't been able to sort (or were a bit conservative of about the ability to save..)

Them is good batting averages!
 

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These pictures show a diode upgrade. They are arranged in such a way as to ensure that the polarity of the voltage picked up from the track is always presented to the chip in a digital manner.

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This shows the square pads where the diodes are situated ....

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The new Schottky diodes are now in place sitting behind the fully refurbished silicone wiring and new infrared LED ....

The early chips in the Scalextric range used 1A silicon diodes but they wasted a lot of energy as heat. This upgrade replaces then with 3A Schottky diodes which run much cooler because they require less energy to do the same job. This is always a good thing for an electronic circuit. The other side-effect is that this extra energy is now available to drive the motor, which in turn makes the car faster as is the case with the Rev H C8515.
 

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Here's a nice one ......... I was asked to produce the flattest chip that I could but it had to be industrial strength and be re-flashed with Incar-Pro firmware ....

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The original version of the C7005 is in the background and the turbo nutter-barstud sits quietly in the foreground ....

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The differences are more easily seen when viewed from a slightly higher angle ....

The MOSFETs where uprated to handle higher amperages and the shottkey diodes, well, they are beauties and Ian Harding's ICP firmware is simply brilliant with hotter motors. Getting rid of the analogue baggage is so cool .....
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This Repair may or may not appear on terrestrial in the near future .....
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Thanks Andy, this stuff has been available for some time, it is often referred to as the "Full Monty".

it looks as though the "Full 9-yards" will have to be offered which will include silikone wiring and a capacitor mash up.
 
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Discussion Starter · #289 ·
Here is a C8516 in a Mini Cooper which was recently flashed with InCar-Pro.

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It was a bit fiddly but the old two-glasses trick saw me through ..... :)
 

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"Can I send you some chips for re-flashing to InCar-Pro?" was the question ..... and this is what arrived ...

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A sandwich bag full of chips .....

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it appears that "some" actually means 10x C8616s and 15x C8515s ....
 

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Here's one that wont see another birthday ......

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Some very stressed out components, quite crunchy to the touch ....

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There was not a lot left after some gentle cleaning. The copper tracks are vapourised and layers of the PCB are long gone .....

Oh well, you can't win them all .....
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No worries ..... the ones that I was able to repair should be tough enough now to withstand the aggression ...

Have fun with them ....
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Hi Greg,

As an electronic and repair technician, I'm impressed with your skill and perserverance with these very small chips/decoders.

I wish to ask your thoughts on this... I have built a few DIY Carrera decoders, schematic here: http://redlichelectronics.de/decoder_DIY.html

I have had two failures, both after a moderately heavy crash. They both seem to have failed in the same failure mode. The PIC chip output pin for the throttle goes faulty. In normal operation the throttle output pin goes high during the active swing of the PWM throttle duty cycle (noting this circuit uses separate throttle and brake output pins from the PIC chip) and goes to base of Q3 NPN buffer transistor via internal 47kohm resistor turning Q3 on which turns on the motor drive P channel MOSFET by taking the gate low.

Since the only connection to the PIC throttle output pin is via the internal 47kohm resistor of Q3, I just don't get how that PIC output could go faulty. I have checked the output MOSFET and its fine and is still working. Q3 seems ok on a multimeter but yet to do further checks. So on the bright side all I have to replace is a 14 pin TSSOP package SMD hahahaha... Actually I did one on another control circuit just last week, not too hard really. I will also change Q3 just to be safe.

Wondering what your thoughts are. As far as I see, the output pin is relatively protected. Internal resistors measure series resistance correctly between base and emitter of Q3 so I have no explanation apart from the silicon didn't like the shock from the crash. Even if EMF was emitting from the motor, it shouldn't have affected the PIC output pin like that.

Thanks,

Steve.
 

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Discussion Starter · #295 ·
Great work on your decoder

The µ-processor gets put under a lot of strain whilst a car is being raced. Notwithstanding the constant cycling between accelerating and braking, the communications with the powerbase then there is the hostile electrical field to contend with. If you have ever run your cars in the dark, you will have seen the magnificent display of sparks due to the numerous transient short-circuits experienced during the course of a lap.

A lot depends on how hot the PIC is running at ....... heat will start to edge it towards thermal shock and if a physical shock is added to the mix, then an overall failure is highly likely. I would also look the input side of and possible injection of current during a short-circuit.

At the end of the day ....... you are always going to get the odd few that are beyond repair and only two failures is a very good batting average ..... :thumbsup:
 

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Fair conclusion I think Greg, I should add that I definately was not the author of the design mentioned, just in case that wasn't clear! Just a builder. Both failures the car had been running for a good 20 minutes (so thermal is quite possible) followed by a hit, so good possibility. I think the headlights are also stuck on now (another output pin) but flicker a bit which is a possible internal short in the micro, but interestingly the ID LED output is fine.

Thanks for your thoughts.

Steve.
 

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Discussion Starter · #297 ·
Before you do much in the way of replacing components, Steve .......... have a go at reflashing the firmware in the PIC ...
 
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Before you do much in the way of replacing components, Steve .......... have a go at reflashing the firmware in the PIC ...
Greg, I was about to start probing about... and then I thought the same... Since some functions worked (car ID) but others didn't, I wondered if something had locked up with some bad data. But... no.

Spent an hour or so probing about with CRO, checking voltages etc when I realised the chip was not receiving any data... The car ID would not change when I sent it the command. Noticed there was an acoustic noise coming from the decoder, at first, I thought it was the silicon in the MOSFET suffering from some abuse (having worked on power amplifiers I'm familiar with the sound of FETs or BJT's suffering from bad or overdriven input) but then after the mentioned ID not changing, I checked the data input to the micro. It was just noise. All the input components (voltage divider) checked out OK. By now I was getting confused so I had a look at the data on the track rails and noticed it went to noise when I put the car on the track. So checked all the bypass and power supply caps, and started pulling them out of circuit one by one and waddya know... a filter cap was acting as a short at the frequency the data was running at!

End of the story, it was all my fault! I had difficulty sourcing the specified regulator and had substituted a bigger one. Which I had to put in close proximity to one of the bypass caps. And the heat of the reg had killed the cap! It was hidden from view but once I removed the reg I could see that the ceramic SMD cap was a bit more brown than the others. I will see if I can find the cap and post a photo next to one of the natural colored ones. In retrospect, I remember thinking at the time of assembly, I hope this dosen't cause any issues... But promptly forgot all about it as the decoder had been working very well for several months. The shock of the impact when the cap was already prematurely aged and hot must have been the last straw for it.

Thanks for the interest!

Steve.
 

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Discussion Starter · #299 ·
Nice work Steve, great perseverance got you there ..... :thumbsup:
 
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