| Electronics > Repair |
| Amiga 600 ... maybe Gayle problem ... |
| (1/3) > >> |
| saronno:
Hi, I am trying to repair and amiga 600 and I noticed (with thermal cam) that gayle is cold. Then I checked the gayle's vcc line (is present) and check also kb_reset. Now ... --- End quote --- The pullup resistor is good. The impedance to ground from _kb_reset is 1kohm ( Too low?). R514 is ok. The voltage at the base of the transistor is slighty short of 0.5v (when a600 is powered up). Even when amiga is not powered, impedance to ground is just 1kohm .... to me it makes no sense you have just 1kohm to ground because if so, the pullup resistor can only rise the voltage to 2.5v if the transisto r is not in a conductive state. I put 3v on the kb_reset line to see what is getting hot .... it is the gayle chip. Is it dead? Is it kb_reset active low? If so, why is gayle cold? TIA |
| m k:
Underline first indicates it's active low. First R514 activates Q511 and later U14 pulls R514 down. 0.5V is 10% of Vcc, so R514-R515 divider is as it should. How much is from _KB_RESET to GND? |
| saronno:
I actually solve the problem changing the 555, but now, I have another problem: Amiga start, it shows light green, followed by two lighter tone of green .... then white screen. I check cpu, ram and rom .... there is dialogue going on ... maybe a crc error in the rom? |
| Andy Watson:
Do you have facility to check the power supplies? Not just voltage, but ripple too? |
| saronno:
--- Quote from: Andy Watson on May 10, 2024, 06:57:41 pm ---Do you have facility to check the power supplies? Not just voltage, but ripple too? --- End quote --- Yes, I have a scope. There is a about 300 mV peak-to-peak on 5v. Anyway, I try to add a big cap on 5v rail but nothing change. |
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