Technika 206 DAB radio NO AUDIO

[notallbad]

Before Dab is crap rants, I quite agree but would like to try and repair if possible.

The radio all worked fine however DAB function was never really used due to lack of reception.

The radio was left in standby (running on Mains supply) over night out in the workshop, couple of days later and the audio has stopped working.

It all appears to be working, i.e tunes into stations (signal strength bars indicate this), vol +/- control, menu functions etc...

When switching betwen DAB and FM there is a pop/crackle (not really sure how to explain it) come through the speakers and the LED display dies and comes back to life.

I have checked the headphone jack hoping the connections had shorted with corrosion but no such luck! No audio through the headphone jack either.
Also powered it up from a DC power supply with no change.

Unfortunately there is no Aux in jack to try.

I am somewhat suspecting the fault to lie with the Radioscape RS220 (RF tuner and DSP plug-in module).

Photos to follow with component identification.

[notallbad]

Re: Technika 206 DAB radio NO AUDIO

Also set the Alarm function to Beep but no sound when the alarm was supposed to go off! It can be set to Fm / DAB or Beep on Alarm, no sound from any function.

Attempted a factory reset, power up from mains whilst holding in the 'Select' button and still no change.

[notallbad]

Re: Technika 206 DAB radio NO AUDIO

Receives the Date / Time stamp signal too!

[notallbad]

Re: Technika 206 DAB radio NO AUDIO

Re-capped the KSC caps, the 4 bigger main ones on the power distribution/amp board.

[notallbad]

Re: Technika 206 DAB radio NO AUDIO

Casing shell

[notallbad]

Re: Technika 206 DAB radio NO AUDIO

Headphone pcb

[notallbad]

Re: Technika 206 DAB radio NO AUDIO

Tuner / DSP board - Radioscape RS220

[notallbad]

Re: Technika 206 DAB radio NO AUDIO

Power / Amp board

[notallbad]

Re: Technika 206 DAB radio NO AUDIO

Key pcb

[notallbad]

Re: Technika 206 DAB radio NO AUDIO

Mains supply in / transformer / speakers

[notallbad]

Re: Technika 206 DAB radio NO AUDIO

Power / Amp board

component side :

TA8227PG - low freq power amp

HEF4013BP - Dual D-type flip flop

solder side :

LM324 - low power quad op amp

PCM1742KE - 24-bit 192khz audio digital to analog converter

HEF4093BT - Quad 2 input NAND schmitt trigger

[momaka]

Re: Technika 206 DAB radio NO AUDIO

So you did a full recap on the amp board and the issue persists?

If so, I'd start at the TA8227PG amp chip and work backwards. That is, first determine if the amp IC is getting power on its Vcc pin (pins 1 and 12, looks like).

If that checks out, disconnect the two inputs on the amp IC, which most likely will be wired through some input coupling caps. Then feed an audio signal (again through some series coupling caps) into pins 6 and 7. If there is no audio, the amp IC is probably bad. If you do get audio, the issue is somewhere before that then - in which case, start tracing backwards from the signal input pins to see what chip they go to.

[notallbad]

Re: Technika 206 DAB radio NO AUDIO

OK thanks.

Voltages on the TA8227PG
pin 1 vcc2 = STBY 0.5v - ON 12v

pin 12 vcc1 = STBY 13v - ON 13v

[notallbad]

Re: Technika 206 DAB radio NO AUDIO

Where would I inject the audio output from this mp3 player via the headphone left, right and gnd wires?

Do I need to connect the headphone gnd wire to the gnd pin 4 Pre gnd on the TA8227?

Traced back TA8226 pins 6 & 7 to pins 1 & 7 of LM324 Quad amp.

TA8227 pin 6 traces back to R25 33k res, then a 2.2uF 50v elec cap, across a jumper link where it T's off to R107 1K res and Lm324 Pin 1.

Would breaking this jumper wire after LM324 Pin 1 and the R107 res be ok for either the left or right headphone wire?

[notallbad]

Re: Technika 206 DAB radio NO AUDIO

Typo above on Post #14, should read 'Traced back TA8227', NOT TA8226!

Yep, that done it!

Audio coming through the TA8227 on both channels/outputs ok.

[notallbad]

Re: Technika 206 DAB radio NO AUDIO

The TA8227 inputs are fed from LM324 quad op amp which is powered by a KA7805 Volt Reg.

KA7805 volt reg :
Input - 13v
Output - 4.95v

[notallbad]

Re: Technika 206 DAB radio NO AUDIO

PCM1742KE - Audio digital to analog converter

Pin 5 - digital vss - 3.2v
Pin 6 - analog vss - 4.95v

[notallbad]

Re: Technika 206 DAB radio NO AUDIO

How do I inject audio through the LM324?

Same as before with the mp3 player headphone 'fly' lead via the traces on the PCM1742KE, pin 9 AGnd, pin 7 VoutL and pin 8 VoutR??? Of course isolating pins 7 & 8 of the PCM1742KE first!

[momaka]

Re: Technika 206 DAB radio NO AUDIO

How do I inject audio through the LM324?

Same as before with the mp3 player headphone 'fly' lead via the traces on the PCM1742KE, pin 9 AGnd, pin 7 VoutL and pin 8 VoutR??? Of course isolating pins 7 & 8 of the PCM1742KE first!

You got it.
Isolate the audio outputs of the PCM1742KE and connect your input to the LM324.

That said, I wonder why they have the LM324 for and not connect the PCM1742 chip directly to the amp IC. Buffering, I suppose? Perhaps we can get a closeup shot of the LM324 circuit to see how it is connected. I suspect there may also be some kind of "tone equalizing" done with it too.

[notallbad]

Re: Technika 206 DAB radio NO AUDIO

Hope this close up photo shows enough detail.