back to the F1320D

[guitardad]

OK, so I found signal to the IC TDA8950TH input and had no output. Rails are there. Ordered new IC. Replaced the IC and same problem!

ughhhhh

Closest print to the Behringer F1320D is the Mackie TH12A. I also had a diagram from NXP (IC mfg) provided by jazzbass here.

http://www.nxp.com/documents/data_sheet/TDA8950.pdf


I just am not sure how long I can run this board and the IC without it's heatsink. Also on the board is another IC for the HF out (TDA7294).
On this board there is also a 074c IC. Not sure what it is used for unless a buffer of some kind between signal in and the OP IC's. HF works, just teh LF driver IC is not working.

Mute FET's check good.

[Jazz P Bass]

Do you have +5 Vdc on the mode pin of the TDA8950TH ic? (pin 6)

[guitardad]

Do you have +5 Vdc on the mode pin of the TDA8950TH ic? (pin 6)

good call ! Must have been what destroyed the new chip too. I had an open circuit from the volt reg zener and fet circuit and the +v line. I was getting full 26v at that pin (6 mode) via a 10k res from pos rail. Found an open feed thru that connected the res to the zener to restore the 5.6v mode v.

That fixed it! Drove me nuts a bit not having a print to see connections so after removing the replacement IC I figured I would trace those lines back to the components and the associated feed thru's on the pcb. Wasn't easy though. I just knew there wasn't much to this thing so I had to not let it beat me up too badly. LOL

Thanks

[Jazz P Bass]

Dumb as*es.
The Max on pin 6 is stated as 6 volts.
Hooking it up to +26 volts was not very clever.
I guess it always helps when designing circuits to consider possible failure modes.

Glad that you got it working.

[guitardad]

Dumb as*es.
The Max on pin 6 is stated as 6 volts.
Hooking it up to +26 volts was not very clever.
I guess it always helps when designing circuits to consider possible failure modes.

Glad that you got it working.

Yeah well the feed thru connected the ZD regulator and fet circuit to the Vdd supply via that series resistor. If that line opened, it's a full Vdd to the mode pin. I wish I would have verified that prior to putting a new chip in. Save me $11, but yeah I also ordered a spare knowing the unknowns can bite ya!

Factory chip was a bear to get out. They love that glue! Test points would also be nice. Not easy to get measurements with those multiple grounds and not much room to access anything. I had to flip the board over to get those measurements. With no heatsinks, I just fired it up for each measurement then right back off.

I bought some nice insulated probes for these kind of smd units.

Though I've never used these for wedges they seem pretty well designed and sound decent enough when working.

For those wondering, the closest schematic for these are Mackie/Tapco Th12A (minus the DSP)