Denon Logic troubleshooting experiance?

[Zero Cool]

anyone have any experience troubleshooting the logic systems of Denon Receivers?? I have 3 units all the same model that all have similar problems. and a forth unit that appears to have a dead CPU.

The 3 semi working units will power on and will play whatever input is selected. So for example, lets say the tuner was the last selected source. if you power the unit(s) up, that last selected source will play just fine. but if you change inputs, no signal. if you switch back to the tuner (2 of 3 units) no sound either. you have to power the unit off and back on and it will work again.

I have traced the signal coming through the input board right up to the volume controller IC('s). the unit does switch inputs but the volume controller ic has no output after a source selection change. yes those IC's work just fine when powered off and back on.

Without going into ALL of the troubleshooting i have done. I have figured out that it has to be a logic problem. the volume controller IC's use a form of serial communications to control 8 channels of volume, pan, balance adjustments plus other functions like source level matching etc. when a source is selected, the MCU sends a serial type command to the VC IC and the levels and outputs etc are told what to do.

next step is to break out the logic analyzer and see if i can spot whats going on. I am beginning to this this is a form of Alzheimer's for these MCU's and is early evidence of pending failure.

So im curious if anyone has in depth knowledge of these Denon units enough to know what the fix is? simply replacing the CPU board?


Zc

[Enzo]

A schematic?

[Zero Cool]

the pdf if is over a hundred pages. let me see if i can distill it enough to be able to put here.


Zc

[Zero Cool]

IC 203 and 204 are switching IC's that switch between stereo inputs and Multi channel inputs.

Ic's 201 & 202 are the volume controller IC's. these are Toshiba TC94A27BUG 4 channel digital controller IC's. these are Serially controlled from the Microprocessor as is everything else. These IC's are configured to control the 7.1 channels for volume, pan, fader, level adjustment functions etc.

When powered up from cold boot. the units will play just fine with whatever input was selected before power off. the volume control functions work fine. I have not tried to get into the advanced menus and try changing other settings that may effect this. but the volume control function works fine and I have signal into and out of these IC's.

When the input is changed. and this is controlled by IC's elsewhere not shown. I have signal going INTO the VC ic's but not out of it. for example. If i inject a sine wave into the CD input and i switch between the tuner and cd input. I can see at pins 13 & 43 that it is switching between the tuner audio and the sine wave coming in. but no audio.

I can see that there are commands being sent to the IC's. but no audio comes out. I can adjust the volume etc and see activity on the data line (using my scope) when i adjust the volume and switch inputs etc.

I will have to get the logic analyzer out and snoop the buss. I have a nice PC based Logic an that I can capture long strings of data and examine it. even has a bit of decoding software which is nice. But i still need to figure out the command structure etc.


Zc

[Enzo]

Just thinking out loud... well just thinking with my fingers...

Does this unit have memory of any kind? it is programmable in any way? COUld it need re-initialization if so? I just have this mental image of a system with some bogus little number inadvertantly stored in its memory, so instead of inputs 1,2,3,4, when you select one it sees 11,12,13,14, which of course do not exist in its lookup memory so it cannot respond.

I have reinitted enough Ensoniq keyboards and other things that did exactly that. On some units you could look up a memory parameter and find something like 19 where the range was to be 1 through 4.

Reinitialize or "restore factory settings." Just a thought.

[Zero Cool]

there is a way to reset it to factory settings and that's the first thing i do. doesn't change after. it is definitely a failure of some kind. corruption of the program on the CPU or something.