Hi - I have the usual audio problems due to leaking condensers in the audio circuit. I followed the audio repair guide of Anthony and got the following findings so far:
I downloaded the recommended audio utility and started the test... First of all, the audio output volume is fairly low but not unusual distorted as far as I can judge the 1kHz signal. But when playing a game the sound is very distorted and crackling all the times and is hardly recognizable.
I already changed allmost every part in the audio circuit with new ones: U402, U403, C430, C440, C431, C441, C432, C442, C403, C405, C406 and all electrolyte condensers on the whole motherboard (and some resistors within the audio circuit).
The I successfully measured 750 ohms between 8-9 and 13-14 on U402 (power off). But... I measured only 300 ohms between 5-8 on U402 (instead of 20 kOhm as described in the repair guide), whereas between 3-14 I measured the described 20 kOhms.
Unfortunately I don't own an oscilloscope and it would be a bit expensive to buy one only for this task. But I measured the voltages with my multimeter and got the following results (power on / no audio / both cables connected to my 1084s monitor):
U402
-----
Pin 1: +5.0V to +5.9V
Pin 2: +5.8V to +6.0V
Pin 3: +6.45V (changeless)
Pin 4: +11.8V (changeless)
Pin 5: +4.85V to +5.2V
Pin 6: +4.92v to +5.2V
Pin 7: +4.95V to +5.15V
Pin 8: +4.5V to +4.8V
Pin 9: +4.45V to +4.55V
Pin 10: +2.35V (changeless)
Pin 11: +1.59V (changeless)
Pin 12: +2.35V (changeless)
Pin 13: +6.0V to +6.2V
Pin 14: +6.48V (changeless)
U403
-----
Pin 1: +6.25V (changeless)
Pin 2: +6.05V (changeless)
Pin 3: +0.95V (changeless)
Pin 4: +1.6V (changeless)
Pin 5: +0.95V (changeless)
Pin 6: +4.15V (changeless)
Pin 7: +4.5V (changeless)
Pin 8: +11.85V (changeless)
I also measured VREF between GND and C403 => 2.35V.
Any ideas how to proceed ?
Yup, contact Anthony Hoffman via ahoffman(at)clear.net.nz and schedule a diagnostics session & repair!
