TDA7294 (which 'version' to order for Logitech Z-5500)

[petarp]

Hello everyone!

I'm new here and I apologize if I'm creating a post in the wrong section.

I'm kindly asking if someone can help me with the information about TDA7294.

I own an (old) Logitech Z-5500 5.1 Surround PC speaker system, and I'm trying to fix it.

There are 7x TDA7294 amplifiers used on that system (1 per every channel and 2 for the woofer) . The system was manufactured back in 2008.

I was just about to order it from german branch of Mouser (mouser.de) but then I saw that TDA7294 is not being manufactured anymore. Instead there are few other 'variations'.

https://www.mouser.de/c/?q=TDA7294

TDA7294V
TDA7294HS

Some people said that 'V' version is 'vertical' while 'HS' version is 'horizontal'. But looking at specifications (and the look of the amplifier itself) a 'V' version is closer to the original TDA7294.

I'm just not sure which one should I pick. I would need 7 pcs, and since they are not cheap, I would like to pick the correct one.

Can you tell me which one I should pick to put in the place of an old TDA7294's ?

Another question, if you allow me to ask... 'tabs' of all 7 TDA7294's are 'touching' the big heatsink. They do not 'literally' touching the heatsink. There are mica sheets between tab and the heatsink. But those mica sheets are damaged (broken). Could you tell me, should I order spare mica sheets or I could use some other 'material' to insulate TDA7294 tabs from the heatsink? For instance, can I use thermal pads in place of mica sheets (mica pads)? Will that produce some malfunction?

Thanks in advance for your answer.

Kind regards

[Peter BENSCH]

Welcome @petarp, to the community!

Please check whether pins 5, 11 and 12 (pin 1 = left with tab at top, view on the marking side) of the defective TDA7294 are open or whether there is a track connected to them:

• If they are open, you can replace it directly with the TDA7294V
• If there are tracks connected to them, it was the TDA7294S, which had additional bootstrap and clip detector functions and for which there is no replacement

The mica sheet is actually used to isolate the tab, which is internally connected to -VS, from the heatsink. You can replace it with another thin insulating sheet, e.g. thermal pads as used for M.2 SSD or similar. After installation, please check that there is no electrical connection between the tab and the heatsink.

Hope that helps?

Good luck!
/Peter

[petarp]

Thanks for your reply.

I had some free time, so I dissasembled the woofer of Logitech Z-5500, since that is where the amp board is.

I took a picture of the IC. It sais TDA7294. Please take a look:

Also, to be honest, I'm not sure how exactly to check if there are no traces for pins 5, 11 and 12.

What I did is to put my multimeter to resistance mode, and (while TDA7294) was still (soldered) on the board, I did this:

I put one probe on pin 5, and then started touching all the other pins with 2nd probe. It all said 'OL'.

I repeated the same thing with pin 11, and it was the same result (OL) between pin 11 and any other pin.

BUT...

When I put the probe on pin 12, and started touching other pins with 2nd probe, the measurement was different.

Between pin 12 and pins 5 and 11, it was 'OL'.
Between the pin 12 and 14, it was only 0.3ohm (which means they are connected).
According to datasheet, if this was TDA7294 ('V') version, pin 14 is 'OUT'.

Between pin 12 and pin 2, most of the time (with 5 other TDA7294) there was resistance around 20K-ohms, except with 2 other TDA7294 where it was around 8-9K-Ohms. The other pins, while measured the resistance between them and pin 12, gave most of the time 3-4 MOhms.

I also checked resistance between pins 5,11,12 and 'tab' of the TDA IC and it was 'OL'.

So, I don't know if that is how the 'non connected' should be checked but those are the measurements that I got.

If I did the measurements in a wrong way, could you please tell me how to do it properly.

Thanks!

btw.
Here is the picture of the IC (TDA7294) at the 'bottom' side of the board: