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A small box arrived on my doorstep ..... it was from some of my regulars, all the way from Trinidad & Tobago ..... which is one of the more exotic slot car countries of the World ...
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19 chips of all shapes and sizes .... a mixture SP12s, SP15s and 15Bs a good sprinkling of C7005s ...

This little lot should keep me busy and out of mischief for a while ....
 

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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.
Hi Steve,

just out of curiosity, did the car/s crash due to driver error or run away?

What is the Vin max of the reg you used?
 

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Well that was a fun evening ...... almost into the night ....
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No joy with this one running so I went through the usual checks and replaced the usual bits ......... unusually, it was no better ..... dead as a dodo.

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Out came the multi meter and I checked all of the voltages around TR1, TR2, TR3 & TR4 ...... all seemed OK ...

Next, I checked the voltage level across the motor wires, the red and black ones .......bingo - no reading; it should have read ~12.5V DC.The -ve line check out OK but there was no continuity on the +ve line. Continuity was there all the way back to FB1 but no further .....
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Then I spotted the problem ....... the copper track was damaged ....
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Not just damaged but severed ..... these tracks are minute and easy to miss any damage on them ....

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The track was exposed back to copper and a short piece of wire bridged the gap ....

The chip now works just as it should but it was very frustrating as the damaged track was originally hidden by the stretchy glue that is used to anchor the wires to the PCB. There are now two more happy bananas in the world .....
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I love a happy banana! This is probably my favourite thread on this Forum, thanks for sharing it with us Greg
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The batch of chips from Trinidad & Tobago have been completed with only 3x SP15n chips too fire damaged to repair.

Next up ..... a mixed bag of types and versions thereof ....

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The pair of C8515 - Rev Hs in the top left where a curious fix in that both p-Channel MOSFETs had blown. When I tested the chips on my mini-chassis test-bed, the motor ran when the throttle was pressed but hitting the brakes revealed them to be non-functioning.

The usual problem is the n-Channel MOSFETs, in which case the p-Channel gets replaced as a matter of course.

My total for repairs is now at 995 ........... 1000 is beckoning .....
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Hi Greg, question for you, have you ever had a C8515 chip fail in such a way that it only slows the car and not completely fail?

We race Scalex Nascars on a regular basis, but for some reason I couldn't get the #48 car competitive against the other identical cars. I decided to try and get it up to speed as a friend is coming over for Xmas and I need at least four equal cars…so while racing last Sunday we did a bit of experimenting, to bring it into line with the others you had to decease the power to the other cars buy approx. 10%~15%...not ideal because then the other cars could be driven flat out round most of the track!

So, yesterday I checked and swapped the magnets over, no different, I replaced the motor, no different. If you keyed two cars to the same throttle colour and ran the #48 behind any of the others (in the same lane) they would just walk away at half throttle and by the end of lap be 10ft or more clear.

So I changed the chip to a new one…and suddenly it was on pace with the others???

This is the offending chip

Circuit component Passive circuit component Electronic engineering Computer hardware Composite material

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Can it be 'fixed' or is it bin time?
 

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Hi Neil,

I take it that this chip was not always this poorly performing. That being the case then it is likely that something in the drive-train components is failing.

Pop it in the post as this sounds like an intriguing one to fix .........
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Hi Neil,

I take it that this chip was not always this poorly performing. That being the case then it is likely that something in the drive-train components is failing.

Pop it in the post as this sounds like an intriguing one to fix .........
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Hi Greg, I have a feeling it's always been like this, it's only recently that I got the others performing really well and it became noticeable that #48 was lagging behind, and that it wasn't just down to a slow driver.

Since I found this out yesterday I'm having doubts about one of my Audi R8's...I'm sure that should be a lot faster than it is...I'll investigate and get back to you on that.

At the moment I only have one other chip that just plain expired...it didn't even let any smoke out
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...it just ground to a halt halfway down the pit straight
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...once I get a few up together (or someone is heading back to UK) I'll send you them
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Cheers

Neil
 

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Hi Neil,

I take it that this chip was not always this poorly performing. That being the case then it is likely that something in the drive-train components is failing.

Pop it in the post as this sounds like an intriguing one to fix .........
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Haven't been near the cars this afternoon...spent most of the afternoon down at the beach bar
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But these are the before and after chip change times (you're going to have to download and rotate them as I took them in portrait mode)...

Before:

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After:

Output device Tablet computer Communication Device Gadget Computer
 

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The magic 1000 mark is fast approaching ........ this little treasure is #998; it arrived on my doorstep with a sad tale.

It was purchased on eBay ...... what could possibly go wrong?

Carefully, the digitised car was unpacked and placed tentatively on the club track for testing. As it was trundling around track it to suddenly disappeared in a cloud of magical. The car was retrieved and once it had cooled down, the chip was removed and to the astonishment of the new owner,a piece of lead sheet was found to be wedged between the chip and the electronics ........
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After a bit of a clean up, FB1 was found to be missing along with some copper remnants that once completed the circuit ....
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The fix was to solder a new ferrite bead to a fragment of copper and then to scrape away some mask to reveal fresh copper so that the gap could be bridged with a slither of wire - about 20 minutes of effort.
 

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Another small parcel of chips arrived today from the USA ....... a certain Bruce Springsteen tune is running through my head ....
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These need repairing ... a full re-wire wouldn't go amiss either ....

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NO2 has the Magic Smoke Puddle ...

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and here we have ....... the 1000th chip that I have repaired
 

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Hey Greg: Those mine? Which is NO2? Congrats on #1k. Are you thinking, "Born in the USA?" I'm not a huge Springsteen fan. Glen
Not sure if it would be 🎵"Born In The USA"🎶, maybe the chip "Died In The USA"😨 and "Re-born in the UK"😎😂, is this possibly the first post Brexit international trade for the UK, looks like a chip led recovery (excuse the pun) is on the way.🇬🇧

I propose a toast to GregK 🍾🥂🍻 for his great work with chip repairs 🏆, our digital hobby owes you a great deal, thank you very much for your passion and effort, I'm glad I'm only responsible for 1.5% of the global chip repair market 🤕.
 

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continuing from the last post ...........

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These arrived from the US for sorting out .....

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There is more to fixing chips than just soldering new components onto the PCB ..... the LED wires are in a poor state.

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The LED wasn't doing any better either .....

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All re-suited with a full silicone set and booted with new Ferrite-Men ....
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Cue the Boss ........ They were Blown in the USA ... they were Fixed in the UK!
 

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Discussion Starter · #318 ·
Next up, we have another C8515 Rev-H chip ........

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Another one with blown MOSFETs ........... and not to be left out, the R6 resistor decided to join in the mayhem .... :eek:

Not the prettiest of alignments but it does work.
 

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Just a couple of DPR chips ........

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The usual suspect, NO2, has blown quite enthusiastically and tried to involve a capacitor by embellishing it with a heat craze ......

Passive circuit component Circuit component Green Hardware programmer Computer hardware

Upon first examination, this one looked just a gentle, non-dramatic failure. Closer inspection revealed that the small leg on the right had completely vapourised.

What this demonstrates is that you need to examine everything carefully when troubleshooting the cause of a failure. I love the way that these chips still manage to find many and varied ways to fail which makes repairing them all the more interesting.
 

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Discussion Starter · #320 ·
This is my favourite chip of all time ....... the C7006 Saloon chip ...

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The device marked TR4 is the cause of this chips demise. Although devices marked TR2 & TR1 appear to be OK, they will be replaced to ensure the robustness of the chip, thereby ensuring a long digital life ...... :)

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The wiring loom and plug was removed as I thought that these might be over-optimistically short ....... a new wiring loom will be created tomorrow ......

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The devices have now been removed and the PCB has been cleaned and is now ready to receive the new parts ....... also to be done tomorrow ...

One of the problems in working with these chips from the early days of Scalextric digital is that manufacturing techniques used a spot of glue under each device to hold it in place whilst it was being soldered to the PCB. So any one attempting to fix these early chips need to aware of this, otherwise it is very easy to detach the small copper pads that they are attached to whilst trying to remove them .... :eek:
 

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