To get my 14 year old son interested in electronics I purchased one of these modules ready built and with my help he put it into a case and added a 2 x 12v transformer. I measured the AC output and 13 vac between the centre tap and each terminal (26 vac across the outer terminals) before connecting the wires to the PCB.
How when we turned on the supply smoke appeared within seconds so we pulled the plug and set about diagnosing what could be the possible cause. Having checked the voltages again we powered on and again smoke appeared. We then went back to the shop and purchased another amp, but in kit form and I set about building the kit (having lots of experience of building electronic projects). We also purchased a new transformer just in case the original was at fault.
A gew hours later we powered on and to our disapointment the IC began to billow smoke again
I therefore looked up the spec in the datasheet for this device, and as far as I can see the max voltage to the device is 21v. On checking the DC voltage between pins 5 and 7 it’s over 34vdc ! Thinking about it, 26vac between the +v and -v rectified will give in excess of 30v dc which is way above the specs.
Fortunatetly these amps are just a few pounds from RS so I’m going to order some replacements and use a 9-0-9 vac transformer which should provide around 22v dc, however I just wanted to warn potential purchasers of a potential dissapointment, and advise them to either regulate the 12v lines (requires modifying the PCB) or start with a lower ac rated transformer, it could save you a lot of money in the long run.
Just to confirm the transformer is providing 12.96v ac to each of the inputs (va and vb) with centre tap to gnd
DC measured on pin 5 is -17.34 vdc and +17.34 dc on pin 7 therefore supplying a 34.68 dv across the supply rail !
OK now I’m confused. The datashete states
[quote]
Note to the limiting values
For asymmetrical power supplies (with the load short-circuited), the maximum unloaded supply voltage is limited to
VP = 28 V and with an internal supply resistance of RS ³ 4 W, the maximum unloaded supply voltage is limited to 32 V
(with the load short-circuited). For symmetrical power supplies the circuit is short-circuit-proof up to VP = ±21 V.[/quote]
so does this mean that the max limit for a symetrical supply is -21v on pin 5 and +21v on pin 7, or am I right in thinking that its -11 and +11 respectivly ?
I went down to Maplin and purchased the last kit they had (so this is now makes 3 and has cost me £45 !!) - I assembled this kit taking time to make sure each joint was sound. I made one small modification to this board, I soldered a 9-SIL female header where the chip fits so that I could test the supply voltages without risk of frying the chip !
Testing:
Transformer output 2 x 12v @ 2 amp. Actual output 13.2 vac unloaded x 2
Voltage pin 5 = minus 18.64 volts
Voltage pin 7 = plus 18.64 volts
Checked for shorts between pins and heatsink - none found
Checked for shorts on inputs - none found
Powered on with chip removed and no sign of any issues. removed power and inserted the chip bolted to the heatsing with washer fitted and turned on. Instantly smoke came from the same place as all the others - around pin 5-7.
Conclusion:
that the TDA2616 devices in these kits are faulty
or that the design of the new kits somehow exceed the tollorance of these devices (although checking the data sheet the +/- voltages would appear in limits
Hopefully its just the holidays that are causing any non-responce to my postings and some advice will be forthcoming soon
I guessed as much, and you’re right, Maplin don’t carry the TDA2616 which IMO is bad business practice considering they stock so may Velleman kits.
The thing is I’ve built computers (Acorn Atom and ZX81’s back in the '80s) and in recent years developed my own electronics projects including some PIC based items, so I’m quite capable of soldering a handfull of diodes and a couple of capacitors… so it must be poor batch of IC’s, especially as the + and - voltages are within spec according to the datasheet. - Still at least I’ve got a nice collection of heatsinks if the replacement IC’s from RS fail too !
It will be interesting to see how the thing works when I get the replacements from RS components on tuesday - If those don’t smoke then it proves the TDA2616 supplied in the kits were duff !
With a symmetrical supply, the IC can handle up to -21/+21V, so this is not the issue. If the problem is not caused by a short between the IC and the heatsink (assuming that the heatsink was tied to the GND), then we must assume that a bad batch of TDA2616 has been supplied (e.g. wrong printing: the IC is OK, but it is not a TDA2616). We do not have the means to test each individual IC, we must rely on the supplier. We have not received similar complaints about this kit recently, but just in case, please supply an address, so we can send you 3 spare IC’s.
Hi, many thanks for the kind offer to replace the three IC’s. I tried to send you a PM but that function has been disabled on this forum. Please advise of an e-mail address where I can provide the address to send them to.
In terms of the heatsink, I used the supplied insulator between the heatsink and back of the IC’s in all cases. I ran a DVM set to resistance between the bolts and all pins to check for shorts - none were found. If the insulator was used, how is the heatsink tied to GND ? If it was, then this was grounded and there was no insulation then this would cause problems as according to the datasheet the backplane is at the same potential of pin 5 which would be -18v
Many thanks for your confirmation on the voltages, at least it clears that up and removes it from the equation
Well the replacement TDA2616 chips arrived from RS Components. First of all I thought I would test one without heatsink so I pluged it into the board I had modified by fitting female headers to. Connected the input and speakers and powered on - NO SMOKE
Played a song and it played fine with excellent clarity. Powered off and fitted one of the heatsinks using the bolts supplied in the kit. I also fitted one of the mica insulators just as before, and then performed the same test with the DVM to check for shorts between pins and heatsink - None were found, so I re-fitted the chip to the board, re-connected and powered on - NO SMOKE
Refitted the case and left the amp in my son’s room fully working.
My conclusion is that the TDA2616 ICs supplied in all three kits were faulty.
Whilst you have offered to replace the chips, I really have no need for them as I ordered 3 from RS. However I would apreciate a refund for the cost I have incurred as summerised below:
