LINE6 SpyderII-Fireworks-HELP

[retrorod]

I am attempting to fix a Line 6 spyder II Head. Everything lights up...No sound. Initial inspection showed that both TDA7293 amps were burnt and 3 traces broken. I cleaned up the board and repaired traces and installed two new audio amps. Upon powering up, a small pop and a small wisp of smoke. The amp had sound from the left channel but not from the right. I removed the board to check for visible signs of scorching. I saw none so reinstalled to check the voltages. I got as far as seeing 45V and -45v on the end pins of the TDA's and my probe slipped and contacted another leg on the right channel amp and it went off like a pack of firecrackers..Whoaaa! By the time I got the power off, the light show had traveled to the left side amp. Jeeesh! Stunk up the shop as well as fried both amps...again.
Any suggestions?
My plan is to clean up the board again and CAREFULLY re-install another pair of amps. I am afraid by now that there are other components that are compromised? Any Help, suggestions?...Please!

[booj]

I've been asked to perform the same work on that amp. I feel your pain. But, sorry, I don't have any suggestions other than finding something to gnash your teeth on while redoing the entire job. I find that the .055 width braid and a small chisel or screwdriver tip with a VERY gentle touch helps. I cut the old chip body away and leave the leads in. Then I carefully de-solder the hole with the lead in the hole until the lead just falls out. I've been able to get those chips out without any damage to the board. Good luck!

[retrorod]

Thanks Booj, Somehow, its always comforting when someone else "feels your pain" It seems that just as euphoria results in a repair that is good....the dissapointment in a botched repair lasts twice as long..Ha!
I noticed on this amp that there seemed to be no thermal grease between the TDA's and the mica/heatsink contact. Is that correct? I applied some of the thermal white goop anyway. I figured it couldn't hurt!?
Did you succesfully fix the Line6 that you have(had)?

[booj]

Not yet. Getting ready to. Hey where do you get the mica insulators? I can't find those puppies anywhere.
I'll take some pictures of my "technique" and send those out when I do the job.

[Alex R]

Those chips are sensitive little devils aren't they? After you install the new ones and if you have a variac I would bring it up very slow watching both an ammeter on the supply and a DC voltmeter across the output. If that voltmeter so much as twitches there's still a fault. Often these will blow at very low supply voltages and currents, but not usually without showing a wee bit of DC on the outputs.

You will gather that I, too, share your pain. But would add that once you get the hang of these they're not such a hard fix, and since the fault is so spectacular, customers are usually grateful.

Oh check the cooling fans if they have them.

[Alex R]

As to mica, I think you'll be ok with some of that grey clothlike stuff they sell (tent canvas...no...) that transfers heat but insulates, someone will know the name. You cut it to shape.

[retrorod]

Yes, Alex R, They are very sensitive. That chip went off like a pack of chinese sparklers I do have a variac as well as the bulb current limiter.But didn't use them! I will next time. The actual destruction of the chips was initiated by me when I accidently bridged the pins with my DMM probe. No fans on this particular amp. I feel like the mica pads are still OK on the heat sink.... or WERE.... on the initial replacement? How about the 'thermal grease'? Recommended as well?
I am not sure of the material that you refer to....canvas? nylon? kevlar?

[Steve Conner]

One trade name for it is "Sil-Pad" made by Bergquist.

[retrorod]

Thanks again Steve. I checked out the site. Looks like the STUFF! I see where they will send samples. I wonder if a sample is enough to pad two IC's a little over an inch square? That also answered my question about the thermal goop. Apparently, not needed when using Sil-Pad.
I remember reading in an old thread from Enzo maybe, that they always used new Sil-Pad when replacing burnt Ic's. I guess, not trusting the integrity of the old pads.