SHERWOOD R-807 SURROUND AMP

[geobee]

Hi all, this unit has all the correct sound of the relays latching in, and the heatsinks are warming after a while, so the output amp devices are obviously working, but no sound on any of the inputs. Bit of a job to tear down, so I don't wish to just go in ''blind'' and waste too much time on it. If anyone has any ideas on it, that would be great. Cheers.

[bob91343]

I suggest:

1. Explain your setup, control settings and connections.
2. Post a schematic diagram.

[geobee]

It is just on the workbench, with two test speakers plugged into the front l/r main. It is not even giving the test tones when activated on the remote. No inputs are giving any audio output either. It could just be requiring a reset, but I have been unable to find the procedure for that. The user manual doesn't cover it to the best of my knowledge. I don't as yet have a service manual for it.

[SpecialK]

On a couple occasions, I have bought surround sound receivers off Kijiji for nearly nothing that weren't working.  All that was required was to find a factory reset procedure.  That seems to "fix" the no sound issues.

What I have noticed:
- Pioneer has a button called "signal select" on the remote that seems to allow you to listen to a different input than what you are watching.  Denon has a similar v.sel or something.
- during room setup, your receiver will turn off channels that don't have speakers attached.  Say you only have a stero pair, the other 3 or 5 channels will be turned off.  If you are the second owner, be sure to run the setup to enable the channels.

Again, start with a foctory reset in any case.  These things are overly complex, and you really need to start from a default and tweak from there.

[themadhippy]

sound of the relays latching in, and the heatsinks are warming after a while, so the output amp devices are obviously working, but no sound on any of the inputs.

could be the relays are  disconnecting the outputs to protect the speakers from something like DC offset on the output

[geobee]

Thanks to all, yes, the reset idea sounds to be on the right track, only problem being, I cannot locate the procedure to do it.

[bob91343]

You could try holding each button in turn on power up.

[SpecialK]

From an R-507 manual

To reset the AVR's processor:
1 Press the front-panel Standby/On switch toplace the unit in the Standby mode (the StandbyIndicator LED will turn red).
2 Press and hold the SURROUND down button onthe remote control as pressing and holding thefront-panel Standby/On switch simultaneously.
3 When the RESET message "RESET?" appearson the front-panel Message display, press BAND.
4 When the RESET message "OK?" appears onthe front-panel Message display, press BAND

[geobee]

Thank you, you were close, I got it to reset by holding the band button, whilst powering up from standby, and then pressing band when it asked to reset etc. But, to no avail, it still has no audio even after bringing all of the speaker output levels back up. It says in the manual that there is a section where it says ''speakers on/off'', but there is nothing of that nature in the setup list. Due to the lack of tech support here in Australia, it is going back to the customer, I am not prepared to strip it down with no tech support.

[mzacharias]

Always check power supplies first.

There could be for example +/- 12 or 15 volt supplies missing.

If both are gone, the protection circuit will not trigger, simply no sound.

Or, you could be missing power to a DSP section; have you tried a "stereo direct" function, if any?

[geobee]

Relays are latching in, tried direct also, too much of a strip down to go further with it. I am over wasting time on over engineered home receivers. I once had to do them when running a full time business, but now only working part time, I can pick and choose a bit.

[ambrosia heart]

If no sound can be easily solved by a reset button, there is no point in calling a tech for help. 
There are at least 10 reasons for no sound.   In spite of various brands of av amps, working
principles of yamaha, pioneer, onkyo, sherwood and anthem are same  except denon and marantz
due to one more chip involved in digital decoding board.

How to troubleshoot? see pm. Waveforms and their names see photos and pm. 
You must have an oscilloscope at least 40MHz. No oscilloscope no talk. 
Single channel is more than adequate. Follow the steps and read them carefully. 
Oscilloscope clip must be clamped to chassis or large heat sink mounted with 7 pairs transistors. 
Different chips may be used, locate them and searching them on web so as to probe pins concerned. 
Steps sent to you is a shortcut to distinguish which part of the digital circuit goes wrong. 
Do not ask me why and no principle involved. At least 3 pages essay needed to explain principles, otherwise. 

Digital board is the most difficult part in an av-amp. A logical thought and sturdy knowledge is required.  No only hardware
but also software make it no sound.   This explains why no one is able to or dare to troubleshoot an av-amp digital board in
Hong Kong, even authorized service department, let alone Sham Shui Po, Apliu Street. 
Steps involved are top-secret and do not take tech for granted he/she tells you how to do or even gives you a hint/hints.
In Hong Kong, authorized service department, told you to replace the digital board with $3480HKD = 447USD

BTW, direct sound can give a clue to you only if there are some speaker relay indicators on front panel such as onkyo.
Using this method to diagnose will , however, not help you. Your amp does not have debug mode to diagnose digital problem.
Don't worry. Steps I have told you suitable for onkyo, yamaha, anthem, sherwood and pioneer. 


Tell me the results if you want.