gbolton2008
New Member
Hi All, first time poster long time lurker here...
I've got a Pioneer SA-606 which had, until a couple of weeks ago, been giving great service through a pair of Wharfedale Laser 80s. I went out and forgot to switch off the amp (nothing playing) and I returned to a crackling right speaker and jumping VU meter. I didn't realise at the time, but the bass and mid drivers had clearly been catastrophically blown, as on inspection the cones don't even move any more.
I left it off for a week or two as I had other things to be doing and returned to it this week and found that the fault had apparently spontaneously fixed itself. I had been switching it on for a few seconds periodically to see if this might resolve over the two weeks leading up to this point, and the fault had been present from switch on (so probably not heat related). As I had been meaning to deoxit the pots (bit of a crackle on the balance control) I took the lid and front panel off and gave it a bit of a clean (very dusty) and hooked it up to a pair of Wharfedale E20s (What can I say, I like Wharfedales and I don't have a big budget!). All was well until this morning when all of a sudden the right starts crackling. I turned it off immediately (no sign of any damage to the right speaker thankfully) and started investigating.
According to the multimeter it was intermittently putting out between +3 and -40v to the right output. This evening I tried using some freeze spray on the output transistors to see if that made a difference, and it doesn't appear to change anything. Furthermore, I swapped the 2SB618A and 2SD588A output transistors from the left to the right channel, thinking that would at least indicate if they were the issue, expecting the problem to move to the left channel but no difference.
After finding a post where a resistor in the output stage had gone open circuit and put dc voltage to the output I checked the resistance of the big 5w 0.5ΩK and 0.47ΩK resistors that sit between the output transistor pair's emitters (though the circuit diagram appears to suggest these should both be 0.5Ω?) and these appear fine.
Can anyone suggest a sensible approach to diagnosis on this? I've just turned it on again for a moment now and the fault appears to have disappeared again... :/
Thanks!
Edit to add: This is occurring irrespective of input, volume level, tone control etc.
I've also now found that there is a loud thump at switch on which wasn't there before this issue arose, and it's on both channels - it actually flashes the peak LED. Previously there was a slight thump at switch on/off, the switch off thump is a bit louder now too.
I've got a Pioneer SA-606 which had, until a couple of weeks ago, been giving great service through a pair of Wharfedale Laser 80s. I went out and forgot to switch off the amp (nothing playing) and I returned to a crackling right speaker and jumping VU meter. I didn't realise at the time, but the bass and mid drivers had clearly been catastrophically blown, as on inspection the cones don't even move any more.
I left it off for a week or two as I had other things to be doing and returned to it this week and found that the fault had apparently spontaneously fixed itself. I had been switching it on for a few seconds periodically to see if this might resolve over the two weeks leading up to this point, and the fault had been present from switch on (so probably not heat related). As I had been meaning to deoxit the pots (bit of a crackle on the balance control) I took the lid and front panel off and gave it a bit of a clean (very dusty) and hooked it up to a pair of Wharfedale E20s (What can I say, I like Wharfedales and I don't have a big budget!). All was well until this morning when all of a sudden the right starts crackling. I turned it off immediately (no sign of any damage to the right speaker thankfully) and started investigating.
According to the multimeter it was intermittently putting out between +3 and -40v to the right output. This evening I tried using some freeze spray on the output transistors to see if that made a difference, and it doesn't appear to change anything. Furthermore, I swapped the 2SB618A and 2SD588A output transistors from the left to the right channel, thinking that would at least indicate if they were the issue, expecting the problem to move to the left channel but no difference.
After finding a post where a resistor in the output stage had gone open circuit and put dc voltage to the output I checked the resistance of the big 5w 0.5ΩK and 0.47ΩK resistors that sit between the output transistor pair's emitters (though the circuit diagram appears to suggest these should both be 0.5Ω?) and these appear fine.
Can anyone suggest a sensible approach to diagnosis on this? I've just turned it on again for a moment now and the fault appears to have disappeared again... :/
Thanks!
Edit to add: This is occurring irrespective of input, volume level, tone control etc.
I've also now found that there is a loud thump at switch on which wasn't there before this issue arose, and it's on both channels - it actually flashes the peak LED. Previously there was a slight thump at switch on/off, the switch off thump is a bit louder now too.
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