SlotRacer Forum
C7042 dead port repair? - Printable Version

+- SlotRacer Forum (https://slotracer.online/community)
+-- Forum: Digital (https://slotracer.online/community/forumdisplay.php?fid=12)
+--- Forum: Scalextric (https://slotracer.online/community/forumdisplay.php?fid=13)
+--- Thread: C7042 dead port repair? (/showthread.php?tid=4782)

Pages: 1 2

C7042 dead port repair? - Dr_C2 - 12th-Mar-25

A friend sent me a APB C7042 powerbase which had a couple of dead throttle ports to see if these could be fixed.

I believe this fault occasionally happens during plugging-in of wired controllers, and is likely due to static charge effects from the throttle ports onto the microcontroller input pins.

So can the microcontroller be replaced?

The short answer is yes - but it needs considerable care.

The longer answer involved learning how to replace the microcontroller without allowing any solder bridges to occur between any of the 64 solder points. Once a bridge occurs it is extremely difficult to correct.

After three re-fitment attempts on the same APB - success!

And, next time around it should be a bit easier :)

After re-fitment, a continuity check of each of the 64 solder points was carried to ensure all APB functions were restored. This is quite time intensive!

The final step was to flash the v1.009 firmware onto the new microcontroller. The result is a fully functioning APB with all throttle ports operating correctly.

At present, while brand new APBs are still available the best solution for an APB with a a failed microcontroller is replacement of the entire APB. However, with time, and as the stock of new APBs is exhausted the option of replacing the microcontroller may become more attractive.

At least we now know that the microcontroller swap-out is possible using simple lab-bench soldering techniques.

c

RE: C7042 dead port repair? - flat4 - 12th-Mar-25

Hello!

yes, it is very good to know that this is possible. 

I happen to have a dead entry, but I believe it is more "double inductor coil" related than PIC.

Thanks for exploring Dr_C

RE: C7042 dead port repair? - Dr_C2 - 13th-Mar-25

Procedure in outline:

1/ preparation for 64 pin IC removal
- open APB
- disconnect ribbon cable to LED/button PCB by un-soldering. (take care not to damage tracks.

2/ Microcontroller removal
- avoid using a heat gun as this might dislodge nearby SMD components.
- instead flood all four sides of the microcontroller with fresh solder and sequentially add heat to each side using a soldering iron using a sequential circular motion. As the heat builds up the microcontroller becomes free and can be lifted by tweezers.
- check that no excess solder has splashed onto any nearby components.

3/ Fitment of a replacement microcontroller.
- clean the 64 landing pads and add fresh solder. This should create a ‘domed’ solder surface over each pad.
- very carefully position the replacement microcontroller and then spot solder a couple of diametrically opposite pins.
- check for ‘perfect’ alignment of pins over their corresponding pads.
- then using a point tipped soldering iron heat each pin in turn to create a perfect solder bond between the pin and the underlying solder dome.
- repeat until all 64 pins have been resoldered.
- visually check there are no solder bridges 

4/ continuity check
- make sure there is electrical continuity between each pin of the microcontroller and a nearby component which is know to track back to that pin.

5/ re-attach the ribbon cable (in my case I replaced with an FFC cable).

6/ program the microcontroller with firmware using a PICkit on the ICSP 4 pin interface.

7/ if necessary re-program the APB to firmware v1.009 using a correctly wired USB-to-RS485 cable.

Overall conclusion:

The microcontroller inside an APB can be replaced to bring back full functionality when the microcontroller has failed in some way. However, the repair procedure is quite challenging with lots of opportunities for things, potentially, to go wrong. When taking extreme care at each of the above steps it can be done successfully :)

Not for the faint hearted!

c

RE: C7042 dead port repair? - MrFlippant - 13th-Mar-25

Just think! If you offered this as a service in the future, you could make TENS OF DOLLARS! :)

RE: C7042 dead port repair? - Dr_C2 - 13th-Mar-25

Yes - hopefully I have shared enough information that anyone with the necessary electronics skills could carry out this repair. The time consuming part is tracking back to pick-up points for the 64 continuity checks.

Also, the re-connection/replacement of the ribbon cable which links the button/LED board to the main board is quite a challenge.

I would put the repair time at somewhere in the range 2-4 hours.

As you say Mr F, options for the future as and when brand new APBs become scarce and when the second hand market has more APBs with dodgy ports than without.

c

RE: C7042 dead port repair? - woodcote - 13th-Mar-25

Nice one Dr_C  Thumbup

The blue (ID6) port blew on our original WHO Digital APB some years ago. Having said that, we do have at least four APBs in working order - so it'll hopefully be a couple of decades before we need this repair. I shall copy your notes and keep them somewhere safe.

RE: C7042 dead port repair? - Dr_C2 - 13th-Mar-25

Thanks Woodcote… yes let’s return to this around 2045!

Meanwhile, it was a few hours of tech fun :)

c

RE: C7042 dead port repair? - Dr_C2 - 14th-Mar-25

For completeness, here is a zoom-in of the microcontroller pads on the APB main board once the microcontroller has been removed. 

The pad pitch is 0.5mm i.e. very fine.

[attachment=39982]

RE: C7042 dead port repair? - MrFlippant - 14th-Mar-25

Whenever I see one of those tiktok/reel/short/whatever clips of someone replacing a chip on something (usually a phone), they make it look so easy. Just slather some kind of paste on, heat it all up, remove the chip, wick off the old solder, more paste of some other kind, heat it up, put a new chip on, nudge it until it's sitting straight, and then clean it all off.

Methinks it's really not so straightforward.

RE: C7042 dead port repair? - Dr_C2 - 14th-Mar-25

Yes - one option is to use solder paste, position the microchip and then heat with hot air - the microchip should self-align as the solder flows. The correct method is to apply the solder through a stencil using a tiny squeegee. The amateur alternative is to  drizzle the solder paste across all the landing pads and hope for the best as the paste is heated.

With the APB the issue is around access to the area of the PCB where the microchip is located - lots of tall components nearby. Also, lots of smaller smd components nearby that could become dislodged.

Yes - not so easy in this case as those you-tube videos might suggest IMO.

Hence my proposed (and tested) alternative method using the trusty old soldering iron.

c