A7000+ repair tips - Fixed!

[Bwana]

Hi,

I'm trying to fix a A7000+ with a dead (and leaked battery). I spend many hours under my microscope to fix broken traces arround RTC chip.
Here is a summary of what i've done so far:
1. Fix tracks close to RTC chip and replace the chip by a brand new one
2. Fix tracks close to FDC37C665 and replace the chip by a new one
3. Changed all electrolytic capacitors (also recapped the PSU).
4. Verify the I2c line between the SoC and the RTC. All seems good (pull-ups are ok, data/clock is going to pins 181/182 of the ARM chip)

I've now tried to start the board nothing on screen. I tried to keep the DEL key pressed...

I checked all voltages and seems to be fine.
I used my oscilloscope to see some signals :
1. I2c lines are always a ~5V, there is no activity
2. When I try to keep the reset button pressed, I can see different frequencies on LA (Latch address) lines.
BUT the line LA2 doesn't show any frequency on it (I expect to have 16Mhz as the LA3 is at 8Mhz).
When I don't hold the reset button, the LA2 change state indicating connections are good (checked continuity between ROMS and SoC, all is good).

Does anyone have an idea of where to look? Is the SoC dead?

Many thanks!

[Gary C]

The residue from the leaky battery can very easily short out pins on the FDC chip (and others) which causes all sorts of problems

You need to get around the pins and give it a scrub. A toothbrush should be ideal BUT the nylon bristles are a major source of static so its essential to soak the brush in water to discharge any static before it builds.

With luck, thats your problem

[Gary C]

But... I see you have replaced the FDC.

Ah well.

[Bwana]

Hi Gary,

Thanks for the response.

Yes, I replaced the FDC and checked all lines between the SoC and the FDC.
Now, I replaced the SoC (by a 64Mhz speed grade, who knows...) but I still have a dead motherboard.
I also replaced RAM chips, same issue.
I checked ROM with my EPROM burner (read) and compared to what I found online (RiscOS 3.71).

One signal is preventing the CPU to start, but I don't know which one (Checked resets, power supplies, clocks...).

If someone has an idea. I don't know where to look now...

Cheers.

[Bwana]

I finally managed to fix the motherboard!
I found a broken track (D2 going to ROM) close to the SIMM socket.

I'll double check the IDE part because HDD behaves strangely.