BLACK KAM RZ12A V3 BLUETOOTH USB SD LINE IN 12" ACTIVE PA SPEAKER FAULTY AMP PCB

KAM RZ12A V3 Bluetooth with wireless connection

CE ROHS MADE IN CHINA

AC INPUT 240 V / 50 Hz

FUSE : T1.6 A / 250 V

MIC IN

LINE IN

LINE OUT / LINK

Dial controls:

MIC LEVEL

LINE LEVEL

MASTER

TREBLE

BASS

LED's:

CLIP

POWER

UKKAM10194479-12A-3B060118

SD CARD & USB media inputs, also FM radio & Bluetooth, plus the various line & mic sockets, XLR, phono and 6.5 mm jack sockets, see photos.

Faulty, there is no audio output. The speaker hums a bit when turned on, and some faint noise gets through when all dials are turned to max, still not really discernible music. It seems that audio is going into the amp / psu regulator PCB but it is being blocked somewhere and not going through the circuits. The board is a double sided one with traces on both sides and SMD's on the bottom, also some of the top is obscured with black glue.

Measuring powered up with music input on the phonos and also the FM radio mode using a multimeter, and the speaker connected by clip leads:

7 pin connector on amp / power PCB, calling the bottom one nearest the transformer no 1:

1      12 Vdc

2      Earth

3      -12 Vdc

4      Earth

5      12  Vdc

6      Earth

7      Music in (small varying AC voltage detected, bit of a different level between FM and phono line in) 

Power input from transformer, 230Vac in:

Yellow   13.8 Vac

Black     Earth

Yellow   13.8 Vac

Blue      34.5 Vac

Black     Earth

Blue      34.5 Vac

While I couldn't find any circuit diagram online, these readings all seemed plausible and tallied with writing on the transformer, and the USB / SD / radio part with LCD display seemed to work and find tracks on a USB stick and so forth.

I also quickly tried some in circuit diode test range measurements on the various transistor pairs and nothing jumped out as being abnormal or shorted / open, this is very inaccurate and not testing under load but there was nothing really obvious or any sign of damaged components. I would replace the complete PCB myself if I was going to try and fix it, quite likely even if you found the fault it would be some SMD with no identification markings as they often seem to fail.

I am 99% sure that board is the faulty part, and the rest of it seems OK, although the real test always comes when you replace the component to be 100% sure! You could also potentially just keep the speaker and crossover and use it with a separate amp with some simple modifications.

Note that the heat sink compound will need replacing with a fresh application of a suitable non-conducting product if you were to replace the PCB, it has insulating plates between the output transistors and finned rear heatsink. 

While researching looking for details on this model I found someone on a forum thread about trying to fix one who was saying the rating of the output transistors shows it is incapable of producing the output power it is claimed to make, so don't believe the hype you can see in other ads, although they are no different to many other manufacturers of electronic and electrical equipment in this regard.

Lettering on faulty amp / power pcb says:

PSI15A - PCB02 - V1.7

2018 - 4 - 27

F214496

1929

Height 60 cm

Width 38 cm

Depth 31 cm

Weight 11 kg