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Protecting the IC chip for the tuner with 6 diodes

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My tuner on my AX2 has gone wonky- apparently this is a common failure for these amps- mine was an AXSYS that I upgraded.
I came across the discussion below where mentioned replacing the IC chip, and I can handle that.
I've seen a mention of a way to protect the IC chip for the tuner with 6 diodes. Can anyone tell me how I would do this mod?
It looked like ken@rhythmdawgs.com had the mod, so I tried emailing him last month with no response.
Richard Troutman
Huntsville AL
AX2 floorboard interface
by zzdoc on 2007-07-22 22:38:56.7170
The unit is an AxSYS purchased 10/97 and upgraded to AX2 in 10/99. It is in mint physical condition, has never been played professionally,nor has it been out of the house other than to be evaluated/serviced as described. 
Tuner button was replaced in 2000. Several years later the floorboard ceased to interface in channel select mode. The floor board is not the issue. It was mated to another AX2 in the process of doping out the problem, and operated the unit properly. 
The interface has to be re-established in order for me to sell/trade this equipment. Dealers will not accept the equipment "as is". A the time I was greatly disappointed in the failure of the device, and not of the mind to make the recommended repars. The unit has pretty much lain fallow since. 
I had been advised back then, by Sound Repairs in Deer Park, N.Y., that the entire "mother board" had to be replaced..This, ostensibly,on the advice of your technical support staff at the time. If so, what is the cost in parts if available? If not the 'mother board', what other issues might be preventing this system from operating, and what might the parts cost out to?
Re: AX2 floorboard interface
by LemmieTX on 2007-07-23 06:38:30.7500
The original AxSys (and early AX2's) had a known weakness with the communications port for the floor board. The interface IC was susceptable to being damaged by ESD (static) coming in through the floorboard cable. Later models incorporated clamping diodes to protect the IC. 
The comm chip is reference designator U7. The problem usually manifests itself with the amp being stuck in the tuner mode, but the problem you describe would still be consistant with this failure. 
The part itself is only a few dollars. If you don't have any experience soldering surface mount components, then any electronics shop should be able to change out the part for around $30 labor. Replace the entire board? I think I'd try this first. 
Email me offline and I'll get you the specifics of the chip, as well as the modification to prevent this from happening again. 


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Below is the discussion about the diode mod- I just need the specifics for where to put the diodes.


Richard Troutman

Huntsville AL


Reverts to tune mode
by music50511 on 2009-02-06 18:11:19.7120
AX2-212 When I turn the unit on it goes into the tune mode and wont come off.
Re: Reverts to tune mode
by LemmieTX on 2009-02-07 08:58:11.0520
You have a damaged IC. The chip that does the analog to digital conversion for the remote is very susceptable to static. AxSys and very early AX2's had this problem. ESD suppression was added to the circuit later. 
The device is U7, and is a TLC542 8-bit A/D converter. 
You can get them from Digikey, using p/n 296-1333-1-ND. They're $3.42 each. 
If you've never desoldered or soldered surface mount components, find someone who has, or you'll need more than that to fix your amp! 
It's located on the circuit board on the rear of the amp. 
It's an exact replacement of the existing part, so it's still vunerable to ESD. There's a modification that Line 6 added later, and it involves soldering 6 diodes (1N4001) to the floorboard connector on the amp to shut any spikes away from that chip. 
If you email me at ken@RhythmDawgs.com, I'll send you the specifics on that mod. 

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