Debugging a Line6 DL4. Help needed!

[ataro]

Hi!

I hope you can help me fix a dead Line6 DL4 that won't power up and it's giving me headaches.

First, the schematic:

https://www.docdroid.net/JYZyjup/tmp...48780.pdf.html

I disassembled it and made a visual inspection first. Nothing wrong. I did check voltages, all correct till U14. Touched U14 (MAX887) and was very Hot and giving wrong voltages. Pin 7 was giving 0V instead of 3.3v.



A bunch of components are fed by the 3.3v line, with U2 (DSP56364) being one of them.



After a lot of tracking, I found out that if I cut the 3.3v trace near pin31 of DSP56364, the voltage of the whole line is restored and MAX887 operates correctly.



I thought that the DSP56364 was shorted, so I replaced it with a new one (super expensive, BTW) and didn't made an improvement. MAX887 is still very Hot and 3.3v drops to zero as soon as the pin31 of the DSP56364 is connected.

Here's the DSP56364 Datasheet :

http://www.nxp.com/files/dsp/doc/dat...t/DSP56364.pdf

Any ideas on this? What could cause the short?

Many thanks guys

[MarkusBass]

Aren't the memory ICs supplied with the same 3V3 voltage? In such a case I would check blocking capacitors like C26, C33 and others.

The link to the schematic does not work (at least for me).

[Enzo]

So U14 is hot, either it is bad or its output is loaded. You isolated U2, but was it getting hot? You showed yourself it wasn't the problem.

Are any of the other 3v chips getting hot? And those little bypass caps, any of those get hot? Try just lifting those caps off anyway, they are more likely than the ICs to fail.

[Jazz P Bass]

The link to the schematic does not work (at least for me).

Here is the downloaded file.

[ataro]

Many thanks guys!!!

So U14 is hot, either it is bad or its output is loaded. You isolated U2, but was it getting hot? You showed yourself it wasn't the problem.

Are any of the other 3v chips getting hot? And those little bypass caps, any of those get hot? Try just lifting those caps off anyway, they are more likely than the ICs to fail.

Never thought of that! U2 was never getting Hot, but when I lifted it, U14 came back to life and 3v3 rail was showing voltage back, so I suspected U2 was the problem. But it can be U14 not dealing with load, that's true! No other component got hot. Bypass caps seemed fine. I have ordered one MAX887, will replace it and see what happens.
You helped me a lot. Thanks!

[ataro]

Solved: replaced MAX887, the pedal came back to life. Many thanks to all for the help!

[drewl]

Got one of these that has all the proper power supplies, nothing getting hot but it won't engage the relay and doesn't do anything.

The 3.6v zener was shorted, but I'm using DC voltage for now until I order the diode.
I pulled it for now.

Clock oscillator is working.

I will check the switch pulses to the dsp.

Anything else to look for?

[drewl]

Actually all clocks are correct except nothing at DAC test pad which is a clock coming from U7 I believe....