Beetle1303

Seems to have plenty of CM-1090, CM-1065 and CM-1040 here in Asia.

Yes, the block diagram on page 7 is much simpler to understand to trace. Unfortunately, no luck and couldn't find anything that seems to be shorted. Perhaps indeed something shorted within that 12-pin switch... Too much pain to get it off the board...

It seems quite impossible to de-solder and remove just one such switch, but need to de-solder all 5 switches off the board. Then remove the metal faceplate with 4 claws clamped onto each switch... But, before attempting to de-solder all of them, I checked all the switch on contact/continuity with DMM. All tested OK, except for this CD Direct 12-pin switch. The bottom left 3 pins all "shorted" - looks unlikely to be the switch internally shorted, and more likely somewhere shorted in the circuit path. But I am completely lost in trying to trace with a "blurry" schematics... Anyone with better experience with schematics (and eyesight) can see where is the potential short(s)?

Thank you all for the warm welcome! I have some update on left speaker voltage swinging: 1) Replaced TVR701 - no effect, still relay clicking off/on at higher volume. 2) Replaced C706 - seems to be working fine. Measured voltage across R718 - no longer swinging positively and negatively, but still fluctuating between 0 to 2mV range. Turning the volume higher does not exceed 50mA limit I believe that causes relay clicking. I discovered new issue while doing more tests: 1) Holography, Tone Defeat and CD Direct buttons - at volume zero, pressed/depressed will cause a very loud pop on left speaker! DMM shows around 60-180mA range, speaker pumped positively up and returned to normal immediately. Audio continue to play normally too. 2) Tape Monitor and Loudness buttons are OK. I have cleaned all these buttons with contact cleaner few times, but still same outcome. I plan to swap the Holography and Loudness switches around to see if it is due to hardware contact arching when button is pressed/depressed. Will report back later.

Hi, My name is Leon Wong, from Singapore. I am semi-retired, and recently developed hobby and interest in repairing vintage sound systems. I have particular interest in Sansui Receivers and Carver Amplifiers. My main purpose is to learn, and to revive simpler lower entry models for own use for short while, then sell it at costs to fund my next repair projects. I have done a repair on CM-1090 with the help of members in FB Carver Audio Forum. I was advised to come here for more interactive discussion. Here's the status of my CM-1065 that I have done some research after downloaded the SM here: 1) The unit powered up, clicked, green led on, but no light on VUs and volume led. After tracing the schematic in SM - it turns out the VUs bulbs are wired in series and one of them blown. Bypassed it, and the other VU lighted up. Volume led is dead but the wires measured 19vdc 2) Quick visual check - all the power transistors are of different part numbers, so likely all being replaced. 3) Playing CD input seems OK at lower volume, but started clicking off and on when turning up volume slight higher 4) Visual display on Voltage and Current seems to swing quite widely positively and negatively 5) Check speaker output - right side OK, left side swing quite rapidly 6) Check Idle Bias according to SM - right side stable at 1.5mV (later adjusted to 4.0mV); left side unstable swinging widely. My google research shows one of the symptoms: 6. "Motorboating" (Low-Frequency Oscillation) The Issue: If a decoupling capacitor in the driver stage fails, the amplifier may start oscillating at a very low frequency (1–5 Hz). The Symptom: This appears on a multimeter as a rapidly fluctuating DC voltage (e.g., oscillating between positive and negative) rather than a fixed high voltage. I suspect this could be the reason for the behavior observed, and here is my questions: 1) SM schematic is too low resolution and I am having hard time reading. 2) Anyone can help pointing where do I start tracing the potential faulty components? Thank you.