Whats wrong with my SX-1050?

[MarkSmit]

Hi Everybody

My beloved SX-1050 began yesterday to cut out, every time I turn up the volume.

I've got a bit of knowledge of electronics and the inner workings of an amp, so my question is: where should I start looking for the fault?

Any help would be greatly appreciated.

reg. Mark from Danmark.

 

[embrown057]

Pop the bonnet off and start looking at your voltages first. Main rail supply, BIAS... Most all of the 1050's I've seen had more than one problem. They are one of the easiest receivers to work on. Down load the manual from HiFI engine.

 

[zebulon1]

And/or voltages from the Protection board Pins with the set on and volume at min, balance at center. Speakers disconnected.
Note: Pin 3 is in AC.

 

[markthefixer]

ALL good advice.

When turning up the volume causes protects, the protect board (AWM-090)'s C1 and C2 0.22uf 25v CSSA R22 M25 are usually at fault.
mouser [URL='https://www.mouser.com/ProductDetail/WIMA/MKS2C032201B00KI00?qs=sGAEpiMZZMv1cc3ydrPrF7l45uRd9dVhuow1viMb4j4%3d']505-MKS2C032201BKI00 [/URL]$0.42 ea

The CSSA capacitor type is a "solid aluminum" cap, and these eventually fail from an electronic current leak to a dead short.

You COULD futz around with the balance control to figure out which channel. But they both go bad.

edited in Mattsd's capacitor recommendation and my quick grab part number OUT.

 

[mattsd]

Just to add on, the 2SC869 transistors (Q1 and Q2) on the protection board for the overcurrent/overload detection generally cause a lot of issues as well, including tripping the protection too early when the volume is turned up. Most of the protection problems I have encountered are either caused by those or the caps, sometimes both. Replacement is a 512-KSC1845FTA. Just FYI @markthefixer, that cap you suggested has 2.5mm lead spacing and short leads, which will make it slightly tricky to fit as the lead spacing for the .22uF caps is 5mm on this board. 505-MKS2C032201BKI00 has 5mm lead spacing and the tape packaging, which gives much longer leads.

 

[cuda440]

I was troubleshooting what turned out to be a false alarm on my SX-1050 protection board and it got me to look at the BOM again after several months since I had updated it. I noticed that only some of the transistors (Q1, Q2, Q6, and Q7) are recommended to be replaced (KSC1845, KSC1845, KSD1616, and KSC2690 respectively). Q6 is a 2SC945, but there are two more of those on the board (Q3 and Q4) that don't get called out for replacing.

Why is that?

 

[rcs16]

Someone guessing (lacking analysis or facts) at what could fail more often than another. If you are going to change one 2sc945 (suspicious of imminent failure), logically I do not see why you would not change them all, use ksc945c or the others recommended.