Hello
I am asking for your advice on the following issue. I have a Beogram CD7000 with a damaged mechanism and I would like to connect it as a separate DAC using the original CD7000 power supply and analog stage. If it succeeds, I will probably change the analog stage to a tube one. The problem is that the CD7000 has strange controls - the TDA1541 power supply voltages appear on its pins only after pressing the Play button and if the system does not detect activity, they disappear after about 3 seconds. So the question is - how to lock the microcontroller so that the supply voltages remain active after turning on the CD7000? Looking at the attached block diagram, it seems natural to have a permanent short to ground on pin 19 of IC4. Is this a good idea or should something else be done? Thanks for your help.
I am asking for your advice on the following issue. I have a Beogram CD7000 with a damaged mechanism and I would like to connect it as a separate DAC using the original CD7000 power supply and analog stage. If it succeeds, I will probably change the analog stage to a tube one. The problem is that the CD7000 has strange controls - the TDA1541 power supply voltages appear on its pins only after pressing the Play button and if the system does not detect activity, they disappear after about 3 seconds. So the question is - how to lock the microcontroller so that the supply voltages remain active after turning on the CD7000? Looking at the attached block diagram, it seems natural to have a permanent short to ground on pin 19 of IC4. Is this a good idea or should something else be done? Thanks for your help.
I think that on 19, it is not a ground but an interrupted connection.
We need the diagram of the control part
We need the diagram of the control part
The way I understand it is that pressing the "Play" button short-circuits pin 19 to ground for a moment, which is enough for the IC4 microcontroller to send a "Power On/Off" signal from pin 22 to the power supply circuit. Interestingly, the CD7000 does not have its own Power button.
You're going to laugh, I have a CD5500 and I never noticed this detail 🤣
Since the "On" function is inverted.......
Cutting off the trace from pin 22, and shorting the point between R35 and R29 (or before R35) to ground, should keep the PSU always active.
Or do it whith a small single toggle switch, thus making your own On/Off 😉
Thank you @Boydk and @huggygood for your interest in the topic and valuable tips. I will try and report how it went 😉
I still have a question about the correctness of any mods on this CD (NOS mode with applying the I2S signal directly to the TDA1541 pins). Looking at the diagram below, will it be sufficient to remove the color-marked mutating transistors and FET transistors from de-emphasis? I will try to "immobilize" the SAA7220 itself, either by desoldering it or disconnecting its clock from pins 10 and 11. And maybe, just in case, I will remove the servo plate in case the drive itself goes crazy and starts flying away 
Thank you again @Boydk for your help, your advice turned out to be effective, the supply voltages do not disappear. I managed to run this CD as a DAC working in simultaneous mode. The game is very interesting and provides a basis for further modifications of the output stage and power supply.
