A600 stuck in dark grey

[Solderbro]

After a day running with install of the CF Card, one of my A600 won't start up.

Screen stay dark grey
One caps lock blink assumes that the keyboard is okay
No sound from floppy
Green LED at high level, no dimming
No response from floppy and hdd LED.

Tried with same result
- changed the PSU
- removed the ACA020
- removed the 1Meg chipram expansion
- unplugged the CF-Adapter
- unplugged Floppy to trigger response

The machine was recapped in june. Any idea where to start searching, have DMM and logic tester ready for action.

[1NOM155]

Not much but a star to diagnose the error. check out this link http://wiki.classicamiga.com/Amiga_b...r_code_colours

[Daedalus]

So, the power LED starts dim, then goes to full brightness and stays there? Or does it just not change brightness at all when the power is turned on? If you press caps lock multiple times (10-20 times), does it stop responding?

[1NOM155]

under my recent experience could be a solder crack on cpu or bad ram.

[Solderbro]

Did some checks on the reset logic.

Pin 3 what seems to be the output to Q511 transistor base is always on low, so KB_Reset is always grounded. At pin 2 i found at startup a short high, then it falls to solid 0. Changed the 555 for testing reasons with no success.
Will go deeper into that when the oscilloscope has arrived.

[supaduper]

You can use the excellent Diagrom too if you have a eprom burner
http://eab.abime.net/showthread.php?t=89183

[Daedalus]

Originally Posted by Solderbro

Did some checks on the reset logic.

Pin 3 what seems to be the output to Q511 transistor base is always on low, so KB_Reset is always grounded. At pin 2 i found at startup a short high, then it falls to solid 0. Changed the 555 for testing reasons with no success.
Will go deeper into that when the oscilloscope has arrived.

If the reset circuit isn't coming up, then the LED will be constantly dim, not bright. That will give the symptom of being stuck at a black screen. If the base of the transistor was high, then goes low, but the collector doesn't change state, it sounds like the transistor itself is at fault, though there could be a short or a failure in another part that's holding the KB_RESET line low.

[Solderbro]

Checked that deeper with a new 555, Got the high to low change at pin 3 from my 555, so the base of Q511 follows and the collector turns inverted from short low to high. So the KB_RESET is on high now. But nothing else happens, all chips seem to wait for something, there is no activity on data and adressbus on any chip.
Checked availability of +5, +12 and -12V on many corners. What's behind the KB_RESET at cold start?

[Daedalus]

Keyboard reset is used to trigger the other reset signals, like _RST (for the CPU and custom chips) and _IORESET (for peripherals). From memory, it's Gayle that generates the other reset signals, but check the reset at the CPU specifically, see if that's coming back up on reset.

[Solderbro]

Found it, by somewhat reasons a piece of copper has shortened few Gayle pins. This has put some chips into wait state, as first diagnosis most of the system is running now.

[TjLaZer]

Wow! Glad it's working!