You most likely have your External sync set to pocket operator sync. See section 10.7 in the Op-1 manual. It uses the right channel to send sync data, therefore no audio will come thru. I did this once already and was baffled for a few days, I almost bought a new board even!

The most likely culprits are #1 the belt that controls the cassette mechanism has gone bad/loose or broken (1) 2 the switches that control the mechanism are dirty or broken Both would require removal of the unit from the car and you'd need to bring it to a electronics repair shop. Any decent tech would charge $75-125 to do it right. They'd also clean the heads and tape path, so it'll probably sound a lot better once they are done. good luck!

There are a few reasons why this could be happening. If it shuts off right away(5-10 seconds) you are most likely dealing with a bad component, probably a capacitor or transistor. In the case of shutting off after 20-30 minutes, something is overheating or a capacitor/transistor is getting "leaky" once it heats up. It is very hard to be specific as to which transistor or capacitor, but the first place I'd look would be the power amp section and the power supply. One thing you could do is open it up and see whats getting hot, but remember the risk of shock is great. Be careful what you touch. Ideally you are using an infrared camera to see whats getting hot. Any other type of trouble shooting beyond that would require a multi-meter One other thought, does this unit have a fan? If the fan is running slow or not at all? This could cause overheating.

I had the same thing happen too. You can pop open the bottom and take the board out and resolder the jack, but if that doesn't work you just gotta write to teenage engineering and ask to buy a new output board from them or better yet hopefully its under warranty. Its super easy to replace. Theres a guide right here. Teenage Engineering OP-1 Connector Board Replacement Good luck!

Have you tried taking it apart and cleaning the keyboard mat/board with a cloth or q-tip? Sometimes soda or a sugary drink gets spilled in there and in that case use a TINY amount of water and remove it with a q-tip, then make sure to let it dry for a while. Let me know if it works out, thanks!

If its shutting off at a common length of time from cold, then its probably something to do with IC's overheating or maybe power supply. Maybe try blowing a fan on it while using it and see if it lasts longer. If it does its definitely heat related. In that case it won't be the power supply cable. The problem would be related to items on the motherboard, maybe the capacitors. Its also possible that the heat sink is not attached well enough anymore and it might be a good idea to reseed that. Let me know what happens from there.

Parts like that are quite hard to find, my first recommendation would be to just find a "broken" one on ebay and part that out. You would be able to find the same/similar part here Mouser.com or digikey.com, but I must say you have to know what you are looking for. If you can take a close up picture of the switch and the pads on the board I can guide you. Also you'll need to have a soldering iron with a small tip, no cheap clunky radioshack one will help. good luck!

Have you made sure the front panel assembly near the home button has no exposed connections. You can see an example of this here https://www.youtube.com/watch?v=1_hGBxOP... Sometimes those connections can short and cause all sorts of issues.

My first guess is the battery connector is either damaged or has become slightly unsoldered. I would touch it up with some new solder first. If its not that then its probably circuitry related to whatever switches from battery power to ac power. Maybe a loose connection there, but re-soldering that is flirting with disaster if you ask me. I dunno maybe find one with a broken lens and replace the motherboard if you are feeling up to it, good luck

I mean if you are not willing to throw down $13 for the schemo then time must not be a big concern, so just start digging in. I've found it pretty easy to find the place to tap into for a line in. That place usually is the fm output buffer stage. Find the main fm chip, look up the datasheet, find its L/R stereo out and tap in after the output buffer, but before the main selector switch or preamp. Then place your own dpdt switch there, that way you then select between Fm or line in. Its pretty much the only way I've found without building extra circuits. Good luck.