TD-603 channels for blue tooth

[Jungle_Jim]

Hi Ady

OK - that all looks reasonable - though I can't see from the photo if any of the caps are bulging. But the big cap looks ok - not leaking like mine was.

If one side is quieter - you mean front and rear are both quieter in a similar way as compared to their opposites? Um. The volume knob is push for balance? Maybe give that a bit of attention - move it back and forth, spray some contact cleaner in it?

Apologies I still haven't done what I said I'd do and post pictures etc - I currently have a dose of Covid which isn't helping.

John

[Jungle_Jim]

Here's some images...
(Is it possible to make it so these images are displayed, rather than just the links?)

https://drive.google.com/file/d/1B0s...ew?usp=sharing

This is nearly finished before cable-tying cables etc.


https://drive.google.com/file/d/1am5...ew?usp=sharing

https://drive.google.com/file/d/1G4s...ew?usp=sharing

https://drive.google.com/file/d/1BoG...ew?usp=sharing

This shows you where to splice the BT audio signals into the TA7764P chip.

https://drive.google.com/file/d/1tBl...ew?usp=sharing

With the cassette mechanism gone, the left hole was filled with a push-on - push-off button that switches between radio and BT, and the right side now has a 1/8 stereo jack in, which goes to the BT unit. In the middle, I re-used some buttons from something, which connect to the BT unit for play/ff/rw.

The BT unit I used (though there are many to choose from) - was one that's near-identical to this. Try to get one that's APTX (or better) and Bluetooth 5.0 or at least Bluetooth 4.2.
https://www.aliexpress.com/item/3279...d=gZjtaYJFeNXt

The other two circuits I added, which you can see mounted on this top panel (replacing the cassette) are: one was a small circuit board I made which had a DC-DC isolating transformer (to limit unwanted noise and isolate the BT unit), plus the other board was an ebay purchase voltage regulator board. These two boards may be over-doing it, but I wanted the BT to have clean, well regulated power, protected from peaks, troughs, spikes and noise that goes with automotive electrics. So far it's lasted 18 months without issues so perhaps this has helped.

I didn't set this BT unit up so it could do hands-off phone calls - so I can't offer any advice about this (I think this BT unit could do this, but it needed a mike connected).

I would suggest getting hold of a Bluetooth unit, and splicing it into the right spot (on the 2.2uF caps at pins 2 and 19 of the TA7764P), and make sure it sounds ok, then after that, consider replacing electrolytic capacitors (with same-spec but good quality) on the main board to improve the audio quality and give the stereo another lease of life. If you are working with the stereo unit out of the car, and powered by a bench power supply (or car battery), you will be able to get the BT unit working before you need to start putting in the power regulation/protection boards - which only become important when the stereo is back in the car. And once it is all working, you can tackle how you will present the front of the stereo with new buttons etc.

There's a fair bit of detail to go into with this, but this is something.

John

[AdyH]

Many thanks for this - I’m struggling with the quiet left hand side channel so will have to come up with a solution to that now before anything else.

[Jungle_Jim]

Originally Posted by AdyH

Many thanks for this - I’m struggling with the quiet left hand side channel so will have to come up with a solution to that now before anything else.

Ady
This doesn't necessarily have to stop you doing the Bluetooth conversion... if you go ahead with this, then this balance problem may reveal itself once you're working on the unit and checking connections and swapping components etc.
There are several tests you could do:
* Is it quieter on one side no matter the input - eg - radio or cassette? If you bought a BT unit and plumbed it in at the right point, this would give you an input to test the volume of each side.
* If the stereo is out of the car and on the workbench, could you connect the outputs straight from the back of the car stereo, (which are 'pre-amp' level) - into another amp to test output levels - eg I used a small cheap phone/ipod type speakers with a bat powered amp. This was useful anyway when working on the stereo on the bench. You can see markings on the circuit board next to the 6-pin round connector to say what the 4 audio out signals are - eg - Front Left (FL), Front Right (FR), Rear Left, Rear Right etc - you can solder wires at these points to bypass the 6-pin connecter.
This would tell you whether the outputs are the same coming from the stereo, which would indicate problems with the amp or speakers in the car.
* I have in the past had hi-fi amps where one channel was quiet or not working, and it was from the balance knob potentiometer being dirty/knackered, or the volume knob pot might be bad, or even the fader. You could use a contact cleaner spray, and give the pots back-and-forth movement because they may not have been used for a long time.
* Without seeing it I can't say, but bad electrolytic caps in the signal path might be causing one channel to be quiet or dull. Unfortunately testing caps can be laborious because you really need to unsolder them individually and test them off-board with an ESR meter. But 're-capping' is a thing with vintage hi-fi repairers, who will order replacement caps for practically every elec cap in a unit - using good-brand caps, and this rejuvenates the circuit. I did this with my TD-603 - and many of the caps - particularly the smaller elecs - still 'worked' but after 30 years were drifting well out of spec, including the ESR being too high. When I replaced these caps (it cost around £20-25 for parts from bitsbox and took 8-10 hours ish) the stereo just worked well, sounding as good as it would when new, plus, the new caps will last another 20-30 years. Your problem may be gone if you did this.

John

[adammerve]

Originally Posted by Mrbrown

Hello everyone.

I am adding a blue tooth receiver to my head unit and was hoping someone whom has done this before can chime in.

I have been trying to find the left and right preamp channels to tap into for the receiver outputs. I also need to find out whether or not I need to remove and other items online before the preamp.

Again, if anyone has any experience or can provide some help, I will be greatly appreciative.

Thank you!

you could find out which manufacturer made the TD-603 for Volvo, I thought Becker but possibly not.

[adammerve]

Originally Posted by adammerve

you could find out which manufacturer made the TD-603 for Volvo, I thought Becker but possibly not.

Nox Vidmate VLC

[dfelix]

Originally Posted by Jungle_Jim

https://drive.google.com/file/d/1BoG...ew?usp=sharing

This shows you where to splice the BT audio signals into the TA7764P chip.



The BT unit I used (though there are many to choose from) - was one that's near-identical to this. Try to get one that's APTX (or better) and Bluetooth 5.0 or at least Bluetooth 4.2.


The other two circuits I added, which you can see mounted on this top panel (replacing the cassette) are: one was a small circuit board I made which had a DC-DC isolating transformer (to limit unwanted noise and isolate the BT unit), plus the other board was an ebay purchase voltage regulator board. These two boards may be over-doing it, but I wanted the BT to have clean, well regulated power, protected from peaks, troughs, spikes and noise that goes with automotive electrics. So far it's lasted 18 months without issues so perhaps this has helped.

I didn't set this BT unit up so it could do hands-off phone calls - so I can't offer any advice about this (I think this BT unit could do this, but it needed a mike connected).

I would suggest getting hold of a Bluetooth unit, and splicing it into the right spot (on the 2.2uF caps at pins 2 and 19 of the TA7764P), and make sure it sounds ok, then after that, consider replacing electrolytic capacitors (with same-spec but good quality) on the main board to improve the audio quality and give the stereo another lease of life. If you are working with the stereo unit out of the car, and powered by a bench power supply (or car battery), you will be able to get the BT unit working before you need to start putting in the power regulation/protection boards - which only become important when the stereo is back in the car. And once it is all working, you can tackle how you will present the front of the stereo with new buttons etc.

There's a fair bit of detail to go into with this, but this is something.

John

Hi John,

You have done a very nice work there.
I'm trying to convert this radio for my Brothers 245, normally I work with Mercedes Becker radios and have done a lot of conversions.
I followed your way for the audio input at the caps, but the radio then always plays from the BT source, even if its in radio mode.
The module I use is this one:
https://de.aliexpress.com/item/10050...d=q2pVH1aDVCEq

Did you have an idea about this problem?
I replaced already all caps.

Thank you in advance

[Jungle_Jim]

Originally Posted by dfelix

Hi John,

You have done a very nice work there.
I'm trying to convert this radio for my Brothers 245, normally I work with Mercedes Becker radios and have done a lot of conversions.
I followed your way for the audio input at the caps, but the radio then always plays from the BT source, even if its in radio mode.
The module I use is this one:
https://de.aliexpress.com/item/10050...d=q2pVH1aDVCEq

Did you have an idea about this problem?
I replaced already all caps.

Thank you in advance

Hi Felix
Sorry late reply...

If you've done lots of BT conversions you probably know much more than me about this, but I'll see if I can help...

Do you mean that the BT continues playing when you're in radio mode? That's a problem I had - and the following paragraph of rambling eventually says what I did about it....

From memory - it was a couple of years ago: so there's the pressure switch on the cassette mechanism, and when a tape is in, the switch puts it in tape mode, and when out, radio mode obviously. In one of the photos I uploaded there's a pic of the relevant 3 pins on the connector (eg - pins 1-2 - tape is out, so in radio mode; pins 2-3 - tape is in, so tape mode etc) and I used a dual-throw switch to put it into one state or the other. But in fact I used a DPDT switch - because (from memory) I found that the BT unit kept working when in radio mode, so I used the other 'channel' of the switch to turn the BT unit off when in radio mode. The only down side was if you flicked between the two, you had to wait the seconds for the BT to pair again each time.

Does that help?

Also - I have a question for you if you've done lots of these BT conversions: what power regulation/filtering etc do you put before the BT unit? Maybe what I did was overkill, to protect the BT unit from transients, spikes, RF noise etc etc, as I imagined the BT unit would be easily damaged and not designed for such an environment.

Thanks
John

[dfelix]

Hi John,

Thank you for your reply,

I followed your Pictures, and also add a switch, but as long the BT-Module is connected it plays continuously, even if back in radio mode.

It seems you had the same Problem and solve it the way that the BT-Module is only powered if you Switch to BT-Mode.

I was planing to do the switching with a relay. I programmed the module that an output is triggered if the BT-Module is receiving an audio stream, so the radio switch automatically to BT-Mode if you play Music. But this was not working because the Radio was not playing anymore even if I did not play anything on the BT-Module.
So maybe I also need to add a Switch to switch off the power for the BT-Module.

As Power sources for the BT-Module I use the 5V supply of the Microcontroller, that was working fine.

For the Becker Radio I normally convert I design an additional PCB so that I could use the original buttons to control the BT-Module

Thanks
Felix

[Jungle_Jim]

Hi Felix

Thanks for your reply...

I hope you solved your issues here - tell us how you got on.

(This discussion is more typical of an audio electronics forum than a car forum but here we go...)

I have several questions about how you're doing your BT conversions (BTW for those who have just joined - that's BlueTooth not British Telecom!):

* Are you saying you don't have any voltage regulation/protection at all on the BT unit - just 12-13.5vdc from within the car stereo? Or are you using those BT units which have a DC-DC isolating transformer? And you haven't had a BT unit fail?

* Are you programming the BT unit itself, or do you use another programmable controller like an Arduino?

(FWIW the BT unit I have has stereo-pair audio lines in, to take audio from a phone or mp3 player, and is set up so if there's audio signal coming Though a BT unit that does this wouldn't solve the issue you have).

Thanks again,
John