Hi. C-100ff does not record. You can hear something there but very quietly. It plays tapes recorded on other equipment very well. The heads look good optically. Rec/Play and function switches cleaned. Vu indicators indicate correctly during recording. The headphone connector cleaned but behaves strangely when listening through headphones. When the balance is set in the middle, you can hear both channels but somehow quietly. After setting to the left or right channel, you can still hear both but louder. What to check?
So it records and when played back on the same or another machine it sounds muffled? I don't do a lot of deep dive repairs but the simple ones for me are to clean all the knobs and switches, over here we have DeOxit and FaderLube, you probably have similar EU Products. The FUNCTION switch causes the most issues with sonics. If it's open I'd also clean the Record Bar Switch https://stereo2go.com/forums/threads/sharp-gf-7850-hiss-problems.2803/ I usually get the hiss when mines dirty. I'd also do a good cleaning around the MIC level knob and check the inside wiring around it since your having issues with headphones. Headphone jacks took a beating when used and they get corroded, wires break or metal bends. I usually get an idea on new to me boxes by just playing with the FUNCTION, BALANCE or BAND by turning them really fast to see if sounds comes in for a second.
Also check your tape, the little foam pad under the tape that pushes it against the head can fall apart over time.
Thanks for the answer. As for your first question, that's exactly how it is. As for the switches you're talking about, they were cleaned as thoroughly as I could get to them without taking them apart with a product like Deoxit, which is popular in my country. As far as I can tell, they behave correctly. But I'm wondering about the recording/playback bar. I cleaned it with a spray and moved it many times. Or maybe there's some cold solder there..? The Monitor connector seems to behave correctly. But you can't set the balance there.. right? You can hear both channels clearly. The headphone connector still behaves strangely as I wrote. As for the Mic mixing connector, I'm not entirely sure because I have a crappy microphone. But it seems to work. I also cleaned these 3 connectors as much as I could. It's hard to explain exactly because I have to use an interpreter. online. So... both decks play well. Aux works well. Radio too but it lacks stereo (I checked that VR001 does not respond to position changes). Currently I use it as is. Before I take it apart again I would like to prepare because it is tiring. I tried to check the wiring carefully according to the available diagrams. It looks ok. In fact you have to be careful because old wiring can unsolder. When this C-100 came to me it had traces of interference inside by a possibly incompetent person. For example there is no core from the MSSI system solenoid. Many capacitors on the AMP board were replaced with new ones with the right parameters because I checked. I do not know the history of this C-100. As for the cassettes I checked on a few. They are new.
