TDA7269

[BradC]

G'day all,

Have a little bookshelf stereo I dug out for the lad. It's probably just over 20 years old, so while I can't find a user manual on line I have found the factory service manual. Yay for schematics and PCB layouts!

It's a pretty basic system with a TDA7269 power amp. The left channel cuts out after a while. Disconnect the speaker for a bit, hook it back up and it comes back to life. The right channel keeps on trucking. This happens at any volume, so I'd be surprised if it's thermal.

I'll pop the covers on the weekend and thankfully the power amp PCB is on the outside, track side out, so should be easy enough to get to with the CRO.

There's not a lot of info on its built in protection mechanisms in the data sheet other than short circuit and thermal. Given this is a pretty ubiquitous chip, I thought I'd ask if anyone knew any more about it. Can't be a mute problem because that'd affect both channels, and if it were upstream of the amp then disconnecting the speaker wouldn't reset it.

This is a 7269, not a 7269a (although I can't find much difference between them other than increased power handling).

Like I said, I'll dig out the CRO and sig gen on the weekend, but thought I'd chuck this out first to see if anyone was intimately familiar with the chip.

[David_AVD]

What brand and model stereo?

[BradC]

It's a Sanyo DC-DA3300m. Service manual here:

https://elektrotanya.com/sanyo_dc-da3300m.pdf/download.html

Amp schematic is at the back.

[coromonadalix]

i would check with a meter if dc appears on the defective channel


its a pretty simple amplifier,  swap the speakers to see if the problems persists or change side, if so, the speaker may have problems,  like the coil could partially short on the speaker frame / short by itself

check if all parts between pins 7 8 9 10 11 are ok, good solders etc ... if so,  put the chip in mono  put a small wire between c4740 and c4840  if the problems still stay on the same side


the chip may have internal problems

[David_AVD]

Apart from a chip failure (not common), the usual suspects on units like this are:

• Cracked solder joints on the single sided (non PTH) boards, especially on the speaker terminals and hot / mechanical parts.
• Intermittent contacts on the headphone socket switch portion.
• Speaker relay contacts going intermittently high resistance (no relay in this model).
• Fusible resistors next to the amp chip gone high in value (not applicable this model).