Hello, I've been working on a color classics for a few nights now. Managed to fix the logic board after a recap, several trace repairs and a new DFAC-II sound chip. However, the analog board simply refuses to work. I've already recapped the analog board and replaced 2x TDA4605, 2xCNY17-3 and 2xIRFBC40.
Before recap: No 5v stand-by, crt part is working if logic board isn't installed (high voltage sound and static on crt) but no 5v/12v on hdd connector
After recap and replacement parts: Same symptom. 60V, 24V and 8V generated by crt power supply are all present, but logic board power supply is completely dead.
Took out the analog board again tonight for more measurements, turns out there's no voltage at all on TDA4605's pin 6, which should be charged by RP23 on power up:
Checked RP23 and it's showing correct resistance matching color rings. CP34 and TDA4605 has already been replaced. On the other end of the trace it goes to a transistor connected to the optocoupler on crt's power supply section. Checked the transistor and it's not shorted, the optocoupler is new and crt section is working fine, so I guess I can rule this part out.
Next I tried to bridge power supply's TDA4605 pin 6 to CRT's TDA4605 pin 6 to jump start it. However this pulled down crt's TDA4605's pin 6 to around 2v and it stopped working as well..
Next I tried to cut the trace that goes to the transistor. This sorta worked, voltage on pin 6 jumped to 10V on power up and power supply tried to start, then it started to make ticking sound at around 3Hz:
Checked pin 1 on TDA4605 which is voltage regulating pin according to datasheet, it jumped to around 4V for a brief second, which I think triggered the power ic's overload/short circuit protection:
Checked resistance reading on all secondary voltage pins and they all look fine, no shorts. Also desoldered 2 schottky diodes and they're not shorted. Actually I get 12V/5V on HDD power plug before power supply enters protection mode. Also tried to connect a hard drive to the plug, same issue. Maybe the voltage feedback part isn't working? Checked all smd components and didn't find anything. Also tried to adjust the potentiometer but power supply keeps ticking through the whole range. Also cleaned up the whole section with alcohol just to make sure there's no leaked electrolyte on them, still no dice. Even swapped mosfet, driver ic and optocoupler between the crt part and power supply part, crt part still works so they're not the issue.
I even desoldered the transformer and measured inductance of each winding, no shorts:
Well at this point I'm out of ideas. Anyone had similar issue with CC analog boards? What to check next?
I'll try to figure out the deal with the trace i cut that connects pin 6 of power supply's TDA4605 to the transistor on crt's part, see why pin 6 is pulled to ground with this trace intact. I'm still leaning towards some voltage feedback issue, but I've already check all smd components... I'd really appreciate your input on this.
Before recap: No 5v stand-by, crt part is working if logic board isn't installed (high voltage sound and static on crt) but no 5v/12v on hdd connector
After recap and replacement parts: Same symptom. 60V, 24V and 8V generated by crt power supply are all present, but logic board power supply is completely dead.
Took out the analog board again tonight for more measurements, turns out there's no voltage at all on TDA4605's pin 6, which should be charged by RP23 on power up:
Checked RP23 and it's showing correct resistance matching color rings. CP34 and TDA4605 has already been replaced. On the other end of the trace it goes to a transistor connected to the optocoupler on crt's power supply section. Checked the transistor and it's not shorted, the optocoupler is new and crt section is working fine, so I guess I can rule this part out.
Next I tried to bridge power supply's TDA4605 pin 6 to CRT's TDA4605 pin 6 to jump start it. However this pulled down crt's TDA4605's pin 6 to around 2v and it stopped working as well..
Next I tried to cut the trace that goes to the transistor. This sorta worked, voltage on pin 6 jumped to 10V on power up and power supply tried to start, then it started to make ticking sound at around 3Hz:
Checked pin 1 on TDA4605 which is voltage regulating pin according to datasheet, it jumped to around 4V for a brief second, which I think triggered the power ic's overload/short circuit protection:
Checked resistance reading on all secondary voltage pins and they all look fine, no shorts. Also desoldered 2 schottky diodes and they're not shorted. Actually I get 12V/5V on HDD power plug before power supply enters protection mode. Also tried to connect a hard drive to the plug, same issue. Maybe the voltage feedback part isn't working? Checked all smd components and didn't find anything. Also tried to adjust the potentiometer but power supply keeps ticking through the whole range. Also cleaned up the whole section with alcohol just to make sure there's no leaked electrolyte on them, still no dice. Even swapped mosfet, driver ic and optocoupler between the crt part and power supply part, crt part still works so they're not the issue.
I even desoldered the transformer and measured inductance of each winding, no shorts:
Well at this point I'm out of ideas. Anyone had similar issue with CC analog boards? What to check next?
I'll try to figure out the deal with the trace i cut that connects pin 6 of power supply's TDA4605 to the transistor on crt's part, see why pin 6 is pulled to ground with this trace intact. I'm still leaning towards some voltage feedback issue, but I've already check all smd components... I'd really appreciate your input on this.