K4003 voltage issues

Kits Audio Hi Fi Projects
1

Hi,
I’ve just purchased k4003 few days ago and have assembled it correctly according to the instructions that came with it.
The only difference being that i purchased 2x12V 35VA torroid transformator with two separate secondary coils (no central tap) instead of a 50VA one (they were out of those). I hoped the 35VA should suffice.
At first i wrongly connected the transformator by connecting the leads of a single secondary coil to VA and VB (no connection to GND).
I tried the unit out and at first it started working correctly but after few seconds it just muted. I disconnected the power and reconnected and again the unit worked for only a couple of seconds. At that point i thought that the 1.5A on the secondary coil would not suffice so i figured connecting the other secondary coil in paralel would give the full 3A with 12VAC. I did so and there was no change in behaviour. I took a second look at the manual and realized my mistake, according to the manual the unit needs both secondary lines connected so that the GND is connected to the GND wires of both coils and the VA and VB each connected to it’s own live lead.
i reassembled the unit in the suggested fashion thinking i corrected the mistake. I read 27.2V between VA and VB and 13.6V between VA and GND as well as 13.6V between VB and GND and went on to try the unit again. As soon as i connected the unit to power, the IC blew smoke. I was puzzled. I figured the unit was damaged with the original power wiring i had done and went to the shop to get a replacement IC. Got the replacement, removed the old one, placed the new one and after some soldering went to test the unit. Again as soon as i connected it, smoke came out. I rechecked all of the connections, especially regarding the power leads and found no error, everything was according to manual. I went on the forum and searched for what i had done wrong only to find this post: viewtopic.php?f=2&t=1359&hilit=k4003
And i think i’m having the same problem here.
In any case i bought a new TDA 2616 (3rd is the charm :slight_smile: ) and fitted it on the board but i also reconnected the transformator in my original (errornous) way (i.e. in paralel live leads to VA and the grounds to VB) which i figured works for at least few seconds without frying the IC and went to test the unit hoping to achieve my original results. And the results were disapointing as now only one of the channels works fine for 10sec and the other just hums. At this point i relize that i have tried all of the solutions that came in to my mind and have no idea how to make this darn thing work properly. So before i do any further work on the k4003 i want to check some things with you:

  1. Is it possible that the 35VA transformator will suffice to power this unit (as i’ve seen in the data sheet for TDA2616 , 2A is peek power not constant)
  2. What is the correct way to connect a dual secondary coil toroid transformator, i.e. if i apply VoltageMeter between VA and VB should i read 0V, 12V or 24V
  3. Is there any way to test if the TDA2616 is problematic in it self.
  4. What would be the behaviour of the unit if transformator was (2separate coiled torroid) 2x9V 50VA.
  5. can a 2x12V 35VA damage the IC if everything is connected correctly. (due to lack of Amperage) Or would the transformator be damaged instead?

Please reply and thank you for the time you’ve taken to read this.
Regards,

2
  1. transformer rating is fine
  2. please check page 8 of the manual for connecting details.
  3. Not really
  4. Less output power
  5. No, it should not result in damage
3

Thank you for the prompt reply,
However even after rechecking everything, i’m still unable to resolve the issue.
According to page 8 of the manual i should be able to read 24 V AC between VA and VB ( i read 27.2V which is ok as it’s not loaded). Furthermore i read +19.3V between Pin 5 and GND and -19.3V between Pin 7 and GND (this also seems ok as the IC should be able to go to ±21V. I have desoldered Electrolytic capacitors, resistors and diodes and checked them and they all seem to operate appropriately, i resoldered them back on and now all the elements are in place, solidly soldered and i cannot find any problems in the assembly (including the insulation between the IC and Heatsink). But as soon as i connect the IC and plug the transformator into 220V the IC cracks and smoke comes out just above pin 5.
Any suggestions.
Regards,

4

If your measurements are correct, then there is something terribly wrong with your assembly !
Pin 5 should be -19V and Pin 7 should be +19V with respect to ground.
Check the position of the diodes !

5

Yes you are correct, pin 5 is -19.3 and pin 7 +19.3, i remembered the results wrong. Anyway condensers are properly placed :slight_smile:. On the other hand i noticed that from all the soldering and desoldering the PCB got damaged around the IC pins and i corrected the connections with some additional wires to next connection points (according to lines on the PCB) and decided to give it one more go. For what ever reason, the amp works properly now, i guess i damaged the PCB during initial soldering.
In the end, tnx for your help.