JBL On Stage Mirco Class D amplifier

[Ian2125]

Well here goes...
I'm trying to repair a JBL On Stage Micro for a family friend. For those of you who don't know this is a small portable iPod docking station (don't laugh). The audio amplifier has completely burnt out and the manufacturers logo and part number are not visible. As far as I can establish the amplifier is a Class D type, with output filters in a 20 pin small footprint surface mount device. The pinout does not seem to match the footprint of any part I can find. I threfore wondered if anybody knows which part JBL use on this product. I must say I have considering this is a low cost product I am impressed with the build quality of this item and will be interested to here what sort of sound quality it produces. Although an experienced electronics engineer I have had little to do with class D type amplifiers so am using this as a bit of a learning exercise. I have established that the processor on the unit is working and appears to be communicating with the ipod. The analogue pre stages also appear to be functional.
I would appreciate any suggestions.
I guess if all else fails I can graft another part in its place, but would prefer to put the correct part back.
Many thanks

 

[BWRX]

Pictures of the amp in question would be helpful! It should be possible to identify what pins of the package are used for the output, power, ground, etc. Any of those clues would be helpful in determining what chip it is.

 

[Ian2125]

Hi Brian

Thanks very much for the reply. Having contacted the manufacturer (JBL) they very kindly told me that the part in question is a TMPA2155DS manufactured by a company called Taimec. I have not heard of this manufacturer but did manage to find a data sheet on the part. I had already done your suggestion of working out inputs, outputs etc and despite an extensive comparison with all the readily available parts couldn't find one with the same configuration, or indeed pin numbers. I am now left with the dilema of trying to source the part, which seems to be an obscure far eastern part or grafting an alternative part such as the National Semiconductors LM4810SQ in its place. I would welcome your suggestions.

 

[Eva]

This IC may actually have the same pinout as some old discontinued Texas Instruments TPA2xxx or TPA3xxx.

 

[Ian2125]

TPA2xxx

Thanks for the reply Eva. I have looked for obsolete Texas parts but with no success. I will keep looking, but am now starting to think in terms of 'grafting' another device onto the board. Not something I relish doing with surface mount !

 

[Eva]

Is there some space inside the case for another small PCB? You could just disable the old amplifier and use an off-the-shelf module or even an evaluation board with some chip from Texas Instruments.

 

[Ian2125]

LM48410SQ

Thanks again Eva.
I had toyed with the idea of incorporating a small evaluation board within the unit. However the beauty of this unit is that it is so small and there is very little room to fit anything above surface mount height on the board. I have settled to fixing a National LM48410 LLP device onto the board and then wiring to the existing components that can be used ! The LM48410 is a 2 Watt device requiring few external components, it has spread spectrum PWM and requires no output filters ! I assume there is no problem with leaving the existing output filters in place, so to minimise the disruption to the board. The LLP package is a challange to solder to by hand but I have successfully done it before so am willing to attempt it. What started out as a simple repair has captured my interest in Class D amplifiers, As a processor engineers I feel there existance should not have escaped my notice for so long. I read with interest your thread on your self oscillating design, very interesting, excellent PCB layout I must say. Thanks again.