I snagged a broken Linn lk85 the other day, and when I popped it open, carnage! Both chips had basically exploded. On initial inspection, I couldn't see any other damage. When I pulled the board out and looked at the back, one trace per chip (same one) from pin 8 to pin 15, were fried. I replaced the chips and used a piece of wire to replace the trace, and it is now working fine. What would have caused this failure? Overheating due to bad thermal coupling with the heatsink? Shorted outputs? Only info I got from the seller was that it was working in the basement, until one day it wasn't. Also, this particular lk85 uses tda7294, not the tda7293 as shown in schematics and other threads.
It sounds quite good, first chip amp I have experienced. Now I am intrigued as the sound is quite good, and I am interested in building my own chip amp. Anyway, thought I would post up this failure and repair for reference.
It sounds quite good, first chip amp I have experienced. Now I am intrigued as the sound is quite good, and I am interested in building my own chip amp. Anyway, thought I would post up this failure and repair for reference.
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Well done !!
Hi
the only thing i found in the datasheet is the connection is external and this load the cap at the power pin 15 . so this cap was defect too? or the cap C9?
strange because you just change the chip and everything is fine.
chris
Hi
the only thing i found in the datasheet is the connection is external and this load the cap at the power pin 15 . so this cap was defect too? or the cap C9?
strange because you just change the chip and everything is fine.
chris
Those chips have protection, which did not work.
Both went, so not a speaker....
I suspect a voltage spike, and also if the set is from 1998, a replacement of the capacitors is to be thought of.
And advice from the more experienced members as to putting a NTC for soft start, and a MOV or transient voltage suppressor to protect the circuit.
Had a computer loop in restart at friends house, after testing at my place...turned out to be loose contact in neutral in wall socket.
Both went, so not a speaker....
I suspect a voltage spike, and also if the set is from 1998, a replacement of the capacitors is to be thought of.
And advice from the more experienced members as to putting a NTC for soft start, and a MOV or transient voltage suppressor to protect the circuit.
Had a computer loop in restart at friends house, after testing at my place...turned out to be loose contact in neutral in wall socket.
7293 is good for +/- 50V (120 Volts, 100 Watts)
7294 is good for +/- 38V (100 Volts, 100 Watts)
check the voltages
And if needed put the 7293, pin outs seem identical
7294 is good for +/- 38V (100 Volts, 100 Watts)
check the voltages
And if needed put the 7293, pin outs seem identical
He was worried about the cause of the failure.
My reasoning was that a power spike or sudden load caused it.
Possibly it had been repaired earlier, or somehow the chips got mixed up.
Like the fastest lorry in Europe...'Carping critics have maintained that engines meant for the David Brown tractor division occasionally found their way into the wrong machines'
About the Aston Martin, from the Alistair MacLean novel 'The Way to Dusty Death'.
He did say that the schematics and other threads have all said 7293, he did not expect 94s....
So whoever ran it earlier might have red lined it, to use a car metaphor.
My reasoning was that a power spike or sudden load caused it.
Possibly it had been repaired earlier, or somehow the chips got mixed up.
Like the fastest lorry in Europe...'Carping critics have maintained that engines meant for the David Brown tractor division occasionally found their way into the wrong machines'
About the Aston Martin, from the Alistair MacLean novel 'The Way to Dusty Death'.
He did say that the schematics and other threads have all said 7293, he did not expect 94s....
So whoever ran it earlier might have red lined it, to use a car metaphor.
Yeah, interesting, noticed that it does not have soft start from the transformer. It is weird, that just the chip went. It really was a simple case of swapping in new chips and fixing the trace. Its been in use now since the repair in the basement, and it seems to work quite well. Kids don't have to touch it since it will auto on when signal is presented. I believe there is dc protection designed into the board. But if it was being run on 4r, and the heatsink interface had been compromised, I could see that leading to catastrophic failure. The guy I got it from knew it was broken, but didn't have much background on it than that. I can't recall if the hardware holding it together was loose or not. Sounds great. I quite like it, clean form factor, small, sounds good, and requires no touches from the chilluns.
I remember reading somewhere ... when one of the power rails gets disconnected, the chip fails. Check for firm connections.
I have fixed a number of KRK monitors which use tda7294, and detonation of these devices seems to be a common failure mode despite protections circuitry. They do sound good for what they are though.
