Jason Covert
New Member
I have a runaway speed issue on a SL-Q303: when the start/stop button is first depressed the table will speed up and never look back. Nothing changes when you change the speed selection (33/45). When you press stop, the tone arm will whip back into resting position (likely being powered by the platter, so too much physical force being applied) and the platter will eventually slow and stop.
I've dug into the forum and found that there are any number of issues why this could be happening, but I have a culprit in mind, and would like the hive mind's input.
I checked the early suspects (Q201 and Q203) but they were putting out the proper voltage. I reflowed them anyway and the issue persisted.
Using a multimeter I was able to determine that three pins on the IC201 chip are reading at 0V (pins 22, 23, 24), when they should all be at or near ~3V. They all lead (in a serpentine fashion, through Q203) to the FG Coil, which I believe is built right into the PCB on this model thus making its replacement impractical, so I'm leaning towards replacing the IC201 (AN6680) chip.
There was, however, also an issue with a very low reading on one of the pins on IC101 (pin 11). It should be reading at 5.1V stop or start, but I'm getting 1.35V in both states. This pin connects to the Operational Control Circuit within IC101 and is paired to pin 17 on IC201, which gives the same reading.
My questions...
Is the IC101 issue related to the IC201 issue, or vice versa? Is one causing the other?
Do I need to replace both chips? Or just IC201?
Is it possible that the FG Coil pattern has been compromised?
Any input that one can add to the conversation would be deeply appreciated.
I've dug into the forum and found that there are any number of issues why this could be happening, but I have a culprit in mind, and would like the hive mind's input.
I checked the early suspects (Q201 and Q203) but they were putting out the proper voltage. I reflowed them anyway and the issue persisted.
Using a multimeter I was able to determine that three pins on the IC201 chip are reading at 0V (pins 22, 23, 24), when they should all be at or near ~3V. They all lead (in a serpentine fashion, through Q203) to the FG Coil, which I believe is built right into the PCB on this model thus making its replacement impractical, so I'm leaning towards replacing the IC201 (AN6680) chip.
There was, however, also an issue with a very low reading on one of the pins on IC101 (pin 11). It should be reading at 5.1V stop or start, but I'm getting 1.35V in both states. This pin connects to the Operational Control Circuit within IC101 and is paired to pin 17 on IC201, which gives the same reading.
My questions...
Is the IC101 issue related to the IC201 issue, or vice versa? Is one causing the other?
Do I need to replace both chips? Or just IC201?
Is it possible that the FG Coil pattern has been compromised?
Any input that one can add to the conversation would be deeply appreciated.