D9 Missing capacitors

[procharger]

Hi guys I have done a lot of reading but have rarely posted. I would have to say I know enough to be dangerous and am the original owner of this great amp. About a year ago i recapped my AU-D9 and the knowledge in this forum helped me to make my D9 sound better than new. It was working great and after many hours the protection light started flickering simultaneously with very slight static in the left channel. I ignored that for a while then it started going into protection mode. I could cycle the power and it would come out of protection and i would be good to go until the next time. Of course initially the 0v adj at speakers was set along with the bias adjustments. So i suspected maybe a problem with F3259 protection board. Possibly bad contacts in one of the relays because of the scratchy static. While inspecting things i noticed both c13 caps were missing on the main amp board. Funny those are the ones that aren't published in the repair manual. I must have left them to do later and forgot to put them in. I have searched and searched and can not find the value published anywhere. Does anyone know the value for c13 and what damage may have been done if any?

 

[slimecity]

Go here:

https://www.hifiengine.com/manual_library/sansui/au-d9.shtml

Register and download the service manual - the values will be in there.

Are you sure that these caps are supposed to be in there - was there ever something soldered in? It could be a blank space on the PCB used for more than one amp model, that didnt have these caps fitted for this amp. Check the solder side to see if there was originally something soldered in there.

 

[procharger]

I have the manual they are not listed in there. No im not 100% sure but the pads are silver!

 

[pete_mac]

I have the manual they are not listed in there. No im not 100% sure but the pads are silver!

The pads will be silver due to the wave soldering process, but if no components have been installed in these locations, the solder on these pads should be uniformly flat. You'd definitely know if you removed a component from these locations by looking at the solder pads.

 

[Hyperion]

Does anyone know the value for c13 and what damage may have been done if any?

I don't see a C13 on the F-3258 Power Amp Board for the AU-D9, on the board layout OR on the schematic. If it was needed it should be the same as C14 which, as far as I can see also isn't present on this board.

The AU-D11 does have both of the above components present but despite being a similar overall design, has a significantly different Power Amp Board F-3265.

In any case it is unlikely to be a missing component causing the 'scratchy static', but much more likely to be an oxidised switch contact somewhere, or a dry joint, or as you have mentioned, possibly faulty relay contacts which may be oxidised(dirty). If so, the only cure for this is new relays. The flickering protection light, along with the static suggests the static might be caused by a spikey output waveform from the amplifier due to one of the above OR a faulty component - maybe a transistor. So, check your work (dry joint?), and if you haven't done so already, some carefully directed short squirts of DeOxit on the switch contacts and then working the switches a few times might help. (only do this with the unit switched OFF). Also try to see if you can detect if the static is coming from one channel only. No easy answers here, just a potentially long process of elimination.