Hi! I've finally bought a SONY TC-D5M in excellent aesthetics conditions at a resealable price. I've changed its belts and everything is working great except the recording. When I record, the left channel is exactly where I've adjusted while setting the rec level on the VU meter, while the right channel is way lower, exactly as you can see on the picture (I've recorded on a type I tape a 333hz tone from a pc, I've set the record level at 0db using the VU meters of the TC-D5M. The difference in balance between the channels can also be heard through headphones or measured using a multimeter). - I've already sprayed a lot of deoxy on the rec/play switch on the motherboard and moved it up and down a lot without any major difference. - I've also tried to spray the deoxy on the rec potentiometers and move them around but I couldn't increase the rec of the right channel. - Playing a test tape at 400hz, the 2 channels are perfectly balanced. - in some rare occasions, the right channel is also quieter than the imposted rec level. it's very rare and it looks to happen when I record with the cassette recorder upside down but I'm not 100% certain. What can I do?
Fact that R channel sometimes also goes quiet does suggest a connection problem. You would need an oscilloscope or at least a multimeter than can measure AC voltage in audio range to see where exactly the signal is attenuated. Regarding the cleaning of rec level pots, you are reffering to the external ones or the internal calibration trimpots ? You say you couldn't increase the levels of the R channel. You mean no matter how much you rotate the pot, the recorded level doesn't get higher than -10dB on the VU meter ?
I have a multimeter TRMS, but honestly I don't know where to start looking on the circuit. I've cleaned the internal calibration trimpots (RV502 and RV402). The right one (RV502) is maxed out, the left one I cannot remember (it could also be almost at maximum). if I increase the rec level (using the external knobs) I can increase the level of the right channel higher than -10dB.
Here some photos, maybe they can help. (The switch have been sprayed again with deoxy after I took the photo)
Trimpot shouldn't need to be maxed out to obtain recorded levels at least close to the source. The important thing to determine is if this problem is regarding the audio level itself or bias/head. With a sinewave fed at the input, adjust the levels on the VU-meter at a fixed value and check the level at different points (pin 11, 7, 14, 6 of IC401/501). Also check the bias levels getting to the head are actually the same after the bias trap circuit (L401/C430) on both channels. If the levels of both audio and bias are equal, problem can be a worn head or incorrect head height.
Tomorrow I'll try to check the levels as you suggested. In the meantime I'll add some info: this morning I've opened and cleaned the PB/REC switch, it was kinda dirty, I used Svitol Electric and IPA to clean it. Unfortunately, it did not make any difference, but I've discovered that by recording with the recorder upside-down the R channel gets actually as loud or even louder than the L channel (both the REC trimpots are maxed out). Furthermore I've done a test recording at 400hz and 10.000hz to see if the bias was off (recording at -20db on a type I blank tape), I'm attaching a video of the result. There is a small trop between 400 and 10.000hz.-
