Amiga 500 Rev 5 with broken power led signal

riri

Member
AmiBayer
Joined
Oct 19, 2011
Posts
452
Country
Belgium
Region
Oost Vlanderen
Hi

Im having a strange problem with this Rev 5 motherboard , no voltage to the power led , i've already checked connector and no luck
Tried another keyboard and same thing...

Anyone that had this problem?

Thanks:unsure:
 
The signal for the led comes from u7 pin3 and feeds a transistor to drive the led . just follow the status pin back from the keyboard connector to find the transistor after checking the output of u7.
 
a500 led.jpg
Hi , this is the result of the measurements, a little strange, I think...:unsure:
 
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VERY strange! If you ground the base of the transistor does the led come on? Make sure it is the base so you dont short u7 pin 3 to ground.
What reading did you get at u7?

- - - Updated - - -

Did it work before? is the 500 in working order? is it the original keyboard as some 500 variants drive it high and some drive it low!!
A500-CIA-Serial-Parallel-Keyboard.jpg
 
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Hi , and thanks for your time :)

Suddenly the led came on, but not at all brightness and the drive led lit steadily, as in the photo... without the drive same behavior

U7 = 7,4v

This 500 work perfect , its one of the early mobos Rev5. with hitech keyboard.
I bought it some time ago, but I haven't tested it completely.

I have reseat all custom chips , no signs of damage , really in good condition mobo.

P1090999 (FILEminimizer).JPGP1100001 (FILEminimizer).JPGP1100004 (FILEminimizer).JPGP1100002 (FILEminimizer).JPGP1100003 (FILEminimizer).JPG
 
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That is a good grounding point. What do you have on the floppy power? (+12 and +5).
 
Don't understand where the 7.4v is coming from?? On later boards the _led line is used through the 1488 rs232 serial driver chip to control audio output . any connection on yours?
 
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The pin 3 of u7 is now 4,2v (since the disk drive led turned on and the power led give a little bright ) .
I see no connection points to U38.

Can it be , something in the sound filter that dimmed the power led on this early models?
 
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