Sony STR-DE635 receiver no sound, what's blown?

[Netlist]

So, there is no IC1207 on the digital board (contrary to what the schematic says). I did, however find a 5v BA05T (IC1204) and after checking it's three pins none of them are shorted together.

Why not assemble the amp and check if you have 5V at the terminal of IC1204.

/Hugo

 

[anatech]

Hi jamil5454
Hugo has a good suggestion there.

-Chris

 

[jamil5454]

Uh oh.

I just reassembled the amp and now when I plug it in I hear a clicking noise (I think it's the power switch relay) that gets louder and louder until both 8A fuses blow on the AC board. It takes about 3 seconds. Hmmm, what could I have broken? Sigh...

 

[Bigred]

What is broken? Prolly more and more as you continue to replace fuses and power up the amp

 

[Netlist]

Maybe a mica insulator is missing on one of the power transistors.

/Hugo

 

[jamil5454]

Oops, those were required? crap let me find them.

 

[Bigred]

LOL.... sorry to laugh but believe me, manufacturers nowadays skimp out on everything possible and they wouldn't have parts just for the heck of it. YES those were required. A thin film of heatsink grease prolly wouldn't hurt either. Also if there were insulating washers present with the mounting screws. NO SPARE PARTS

 

[Netlist]

If some or more were missing, make sure next time you power up to use a fuse of about half the required rating.

/Hugo

 

[anatech]

Hi jamil5454,

Oops, those were required? **** let me find them.

You're either having fun with us, or ..... oops!

Don't worry. I see technicians forget to install them all the time, or my favorite, the use two (results in overheated outputs).

You must clean the transistors, heatsink and the mica insulators. You must also use fresh grease. If an insulator is cracked or damaged in some way, it must be replaced. Those steps are not optional, sorry.

If this means you must put everything aside for right now, do it.

Can you just install everything for a quick test? Yes. Just clean all the old grease off everything and remount it dry. Don't run speakers for any length of time and keep the volume down.

-Chris

 

[jamil5454]

Alright, I got those insulators out of the trash and applied some Arctic Silver to them and the transistors and still have the same problem. Obviously I thought it would be similar to a CPU heatsink but apparently not.

I will clean the transistors and heatsink off thoroughly and try it dry. I replaced the 8A fuses with 5A instant-blow ones so I should be ok there.

Thanks everyone for your help. I'm learning so much.

 

[anatech]

Hi jamil5454,
Is Arctic Silver conductive?

-Chris

 

[jamil5454]

I think that might be the culprit. So I can fire her up without the transistors screwed in ("dry") for brief, low-volume periods of time right?

 

[anatech]

Yes

 

[jamil5454]

Well, I think my amp is long-gone now. With the transistors totally separated from the heatsink it still makes the clicking sound when I plug it in. I have to immediately remove the cord otherwise the fuses will blow.

I'll try the front and center transistors dry and see if that helps. I didn't mess with those apart from taking out the screw and putting it back in, but that might have an effect.

I'll post back later when I get some time to work on this.

 

[anatech]

Hi jamil5454,
No, those should be fine. First, measure across the leads of all the output transistors. I'm fairly certain you will find some shorted ones.

-Chris

 

[jaycee]

You could also try powering up without the output transistors installed at all. That should work. If your fuses still blow, theres some serious damage besides the outputs...

 

[anatech]

Hi jaycee,

If your fuses still blow, theres some serious damage besides the outputs...

Could always be simple like a rectifier or filter cap shorted.

Either way.

 

[jamil5454]

Well I checked and rechecked all output transistors and none are shorted, either between the pins or between the pins and heatsink.

I noticed I don't get clicking (aka fuses blown) if I disconnect CNS1303, the ribbon connector from the digital board to the front panel/switch assembly, before I plug in the power cord. Of course, the unit doesn't work, but that may be a clue. Or maybe that connector is just the only path to ground the whole unit has.

EDIT:
Wait a second... are the two middle pins on D801 (looks like a rectifier on the DC Board) supposed to be shorted? They are.

 

[jaycee]

They are probably the AC inputs in which case what you are reading is the winding of the transformer. It shouldnt read dead short, but will only be a few ohms

Might be worth you pulling this bridge rectifier and diode testing all the pins.

 

[anatech]

Hi jamil5454,
It might be easier to test if you could remove the transformer connections. Whichever is easier for you.

-Chris