HOW? Mistakenly plugged the audio in - Page 1
Forum section: electronics / repair

author: gojunnyo
author_rank: Contributor
timestamp: May 10, 2020, 03:12:58 pm
content: I have this old mediacom amplifier, I hooked up speakers unto it and stupidly plugged the audio in to the audio in of the television.The correct configuration would be the audio in of the amp should be connected to the audio out of the television. (Of course, we all humans should basically know that, unless being fooled by the two female audio jacks named as Input and Output).After turning on the tv, a familiar smoke of defeat filled the living room, an odor we all kew, the smell of burnt semiconductor.During my visual inspection, the TDA2030 is completely busted.So the question is, Why did my erroneous plugging (configuration) burnt the TDA2030? The amp was working fine before I plugged it in the TV, and I thought that this amp have protection against erroneous configuration.Any thoughts are much appreciated!

author: aqibi2000
author_rank: Regular Contributor
timestamp: May 10, 2020, 04:04:09 pm
content: Ground potential voltages between the two must have been huge between to cause this in my opinion

author: bob91343
author_rank: Super Contributor
timestamp: May 10, 2020, 05:27:41 pm
content: I agree. Plugging two inputs together shouldn't cause any problem other than not working as intended.Some connectors are so arranged as to connect ground first when plugging in. That is always a good idea.

author: TheMG
author_rank: Frequent Contributor
timestamp: May 10, 2020, 11:19:03 pm
content: Pretty good chance it was pure coincidence, and it was going to go up in smoke no matter what you connected it to.

author: Chris56000
author_rank: Frequent Contributor
timestamp: May 11, 2020, 07:02:12 am
content: Hi!Not necessarily coincidental!If your amplifier was designed for balanced push–pull drive, each side of its output connector would have been connected to an output amplifier contained in one of the TDA2030 i.c's., and tf the amplifier and TV are both connected to the mains earth conductor, then it's very likely that accidently cross–plugging your amplifier's into your TV's audio input, one side of which would have been directly earthed in the TV itself, created a direct short–circuit path from one of the TDA2030's output pins to chasis–earth in the amplifier, via the audio input return in the TV, the TV mains earth, the amp mains earth, and back to the negative supply pin of the amplifier i.c., thereby damaging or destroying it!When the correct loudspeaker is plugged in there is a circuit directly between each of the two separate TDA2030's amplifier channels, but both are isolated from earth and one always acts in opposition to the other, enabling twice the voltage and four times the power to be obtained from a given power supply voltage.Normally, the output pins of the TDA2030 are at approximately half the power supply voltage, so a short–circuit path from either of them to either the positive or negative power supply pins risks damaging the device!It is also possible, that the Amplifier may have used only a single TDA2030 operated off a single–supply, but with the earthy side of the speaker connected to a coupling capacitor rather than the live side, again an accidental short back to earth via a TV or another piece of gear risks destroying it!Chris Williams

author: CaptDon
author_rank: Super Contributor
timestamp: May 11, 2020, 02:52:43 pm
content: I thought he said he plugged the amplifier input to the T.V. input??? Thatwould not have anything to do with the output side. Could be the amplifierhad no ground, but had the line filter on the input which could put theamplifier chassis at 60vac above ground (assuming the t.v. was at grounddo to the CATV cable being connected). If this connection were via RCAphono type plugs (which I dearly hate) the hot pin would have hit priorto the ground connection and possibly put 60vac (at limited current viathe line filtering capacitor) directly on the input of the amplifier.

author: wraper
author_rank: Unknown
timestamp: May 11, 2020, 03:01:19 pm
content: Quote from: Chris56000 on May 11, 2020, 07:02:12 amRegardless of how I try to read this, it results in some nonsense. What amplifier outputs have to do with it's inputs connected to TV input, and where you can possibly see return path from amplifier output to TV? If you mean bridge amplifier, then it will have common ground for both ICs for sure. And regardless if it's TV audio input or output, connector GND is connected to TV GND, the only difference is that connecting amplifier input to the TV input, there will be no input signal.

author: Chris56000
author_rank: Frequent Contributor
timestamp: May 11, 2020, 03:12:35 pm
content: Hi!Ah – I misread the OP's description of what he'd said he'd accidentally done and wrote the wrong explanation!It's very possible a large momentary voltage pulse at the moment the OP may have connected the amplifier to his TV may have found it's way to the input line of the TDA2030 and damaged it, or, if the TV had only a two–wire mains lead, the TV chassis could have been floating at "half mains voltage", and the difference in potential between the TV chassis and the amplifier chassis could well have been enough to destroy the TDA2030.In either case, the OP should be able to replace the '2030 to get his amplifier working again!Chris Williams

author: CaptDon
author_rank: Super Contributor
timestamp: May 11, 2020, 05:37:46 pm
content: It is crazy that they often use a pair of .05uf caps from each side of line to chassis.I have seen sparks when trying to connect CATV leads to T.V. sets and indeed yousee about 60vac differential between the tv and the cable. Current limited by the Xcof the capacitors. Sometimes you can even 'feel' the difference between cable andtv while trying to make the connection. Then there is the not so great days of the'HOT' chassis, like NAP 'K' or 'L' series!!! I loved those chassis and they had a greatpicture, but don't drop the cable on the chassis, and don't try to scope it withoutan isolation transformer!!!! That magic smoke is the color of money lost!!!

author: wraper
author_rank: Unknown
timestamp: May 11, 2020, 05:51:49 pm
content: Quote from: CaptDon on May 11, 2020, 05:37:46 pmIt's at least 10 times less.

author: CaptDon
author_rank: Super Contributor
timestamp: May 11, 2020, 08:27:08 pm
content: 10 times less than what??? You don't believe .05uf each side to chassis? I've seen it.Good God man, I've seen as much as .22uf each side to chassis on industrial equipmentas noise suppression. You can measure milliamps of ground current!! No GFI on thatstuff. Ever take a cutter to a CorCom filter..... The big ones have two caps to ground, thena pair of inductors, then two more caps to ground and often two more caps, one acrossthe line input and one across the output side of the filter, some of those are as big as.22uf but they don't effect the ground current when the device is left floating. I have seensparks between ungrounded test equipment and grounded test equipment. The worstI ever saw was a heathkit signal generator with a polarized plug weld itself fast to a B&Ktube tester also with a polarized plug!!!!! Each had the neutral side wired direct to thechassis and one had the polarized plug forced into the wall socket in reversed fashion!!!Tripped the 20A breaker on that one!!!

author: aqibi2000
author_rank: Regular Contributor
timestamp: May 11, 2020, 09:12:49 pm
content: Now you can replace the little amplifier and then repeat the test for us whilst your 2 channel Oscilloscope is connected up to measure both grounds