Denon AVR-3808ci no video, no digital anything

Symptoms

• No video out
• No OSD
• No surround sound

Diagnosis

• Try to determine what all these have in common
• Self-test confirms suspicions
• Check voltages
• Determine area of failure
• Test suspect components
• Pull components that seem suspect for out-of-circuit testing
• Dig for a suitable relacement and test

Link to the service manual here (free, but you need an account. I find this site very useful, but the manual is available elsewhere if you care to look.)

Link to a replacement KSA1281 transistor from Mouser here.

Hello! Long time, no see!

Today's post is about Denon's AVR-3808ci home theater receiver. I picked this really nice unit up off of Craigslist maybe 5 years ago for $100. It was in pristine condition and has served me well. However...

I made the classic error we are all warned about. I was making connection changes with the receiver turned on, and as I was plugging in (or maybe unplugging) an HDMI cable, I saw a tiny *spark* and the reciever's digital functions ceased to exist.

No HDMI, no surround sound, no composite, component or s-video signal, no OSD. Ugh. Jim, she was dead.

I could listen to AM and FM in 2-channel stereo, but that was about it.

So began my quest.

At first, I thought it was the TV's mainboard, as I had read of a similar failure (no picture) many times. I Ebayed a replacement and installed it. D'oh! Lesson (luckily not a very expensive one) learned about jumping the gun before a proper diagnosis.

Time to pull the receiver, find a schematic, and get it on the bench.

Two-hundred and six pages. 11"x17". This is the biggest service manual I've ever encountered. I will give Denon credit- it's very well organized and well labeled. The schematics run 37 pages. About $16 to have them printed 11x17 at Kinko's FedEx Office.

To trace a connecction, there are several pages to navigate. I'm going to cut to the chase, pretend that it didn't take me 3 months on and off messing around with the PDF version getting nowhere, and tell you how I fixed it after finally getting printouts of the schematics.

1. Look at page 7 of the service manual under the heading CHECK WITH TEST MODE. Error information returned  □ ＳＵＢ □□ ＥＲＲＯＲ □０１□ 
2. Pull the top cover and check for a voltage of 3.3v on the TOP CONNECT UNIT (5-6 on page 159 of the service manual).
   
   
   The schmatic we are concerned about is on page 206. On the far left side, connector CW118, pins 4-7 labeled D GND and D3.3V 
   
   
   
   
   
   
   
   
   
   
3. If your problem matches mine, than there will be 0 volts at this point.
4. This points to a problem on the DIGITAL POWER UNIT, board 1U-3817-1 (conveniently still on page 206.) We have to pull this board out. This board is the one underneath the TOP CONNECT UNIT on the side with the transformer. The 2 blue wires in the above photo are plugged into the DPU board.
5. To disconnect the TOP CONNECT UNIT, little locking tabs on the 4 connectors have to be released. I have an old set of dental picks that helped me. It was not easy the first time. The connections are very tight.
   
   
   
6. After you get the TOP CONNECT UNIT unplugged, remove the board that has the optical and coax digital inputs mounted on it on the back panel. The ribbon cable simply unplugs when you pull straight out. 
7. Now, on the DIGITAL POWER BOARD there are 2 plastic standoffs near the top edge and 3 more locking connectors (aargh!) at the bottom of the DIGITAL POWER UNIT. Work gently and carefully, rocking the board and working with the pick.
8. Once the board is out, the component we are interested in is TR815, a KTA1281 PNP transistor.
   
   
   
9. Component selection isn't critical, however, the transistor does need to be fairly hefty, as it is rated at 2 amps and 1 watt. I found a reasonable replacement in my stash and I honestly don't remember the numbers. I do remember it was only rated at 850mA. I would usually upsize, but I am concerned that if this happens again (not me. Someone else forgetting to turn the receiver off. Yeah, someone else!), another component will sacrifice its life to protect the fuses and it may be one of the many ICs that I can't replace. In all liklyhood, the 5-pin voltage regulator IC802 will shutdown (it has short-circuit protection built-in), but that also kills the 5v rail and may damage something more critical as well. In this case, undersizing ensures that the transistor will go first. And I will have this post to remind me what to do to fix it.
10. Okay- where is this transistor. I don't have a great picture of the board out of the receiver, because I didn't think about posting about this in time. But here are some after-repair shots to show where on the board we are looking. 
    
    
    
    
    
    
    
    
    
    
11. Again, your's will look different, as this was after I replaced the faulty transistor.

Congratulations! If all went well, then all is well. Enjoy many more years of your theater, and remember to turn components off before plugging and unplugging!