MCS 3840 Integrated Amplifier - repair and testing

[@zulumax1]

Saw VH live in 1981 at the Cow Palace in Daly City CA. Back when David Lee Roth was lead singer.

[@500jsnider]

My late wife and I never missed a tour...VanHalen was our band. =\//-/=

[@N747PA]

Love these MCS videos. You never know what’s inside until you open it up. So surprised not to see STK’s in there.

[@luvradios]

For real man, STK's were Technics jam forever.

[@500jsnider]

What are STK's?

[@luvradios]

@@500jsnider , STK packs are basically both amplifier channels output transistors and some of the supporting circuitry condensed in to one package, Technics (and others) used them a lot in smaller amplifiers.

[@davedrezTV]

Thanks! Another great and fun video from you. I have learned so much watching you work. Your descriptions are clear an understandable for everyone! BTW - I saw Van Halen so many times in concert during those great years... "me and my buddies" listened to Diver Down over and over....

[@luvradios]

Dave, thanks for checking out the video man!

[@zulumax1]

I have quite a few of those capacitors pee down the negative leg on my Panasonic RX-5250 boom box. Very dark green, but the esr checked very low on all of them, not open. Could still be leaky, shorted, or off value. Found them all by visual inspection for a non related catastrophic failure where there was smoke. One of the smaller regulator transistors shorted while I was on battery power. That would have fried my transformer or diode bridge had I been powering it from mains power. The TO-92 device was shorted E-C, cracked, and burnt to ash! What else could be shorted? 2SD592 NPN device, and nearest current production replacement I found is a KSD471A CYBU by On Semi/Fairchild. The transition frequency is different. Not sure how important that is in a regulator. Stock ft 200 MHz, the replacement is 130 MHz Hardest thing about this hobby is finding replacement semiconductors.

[@luvradios]

Man I should have kept my 5150, legendary boombox! and your last statement is the reason I have harvested OEM parts from junk board for years, I 100% prefer a good used OEM over a substitute any day.

[@zulumax1]

@@luvradios I have an original service manual for it. I bought it brand new in 1982 for $350. Just checked it for wow and flutter was very low with needle bouncing between 0.03 and 0.04% RMS and still has original belts.

[@zulumax1]

@@luvradios Believe me, I have a bone pile of old boards to pick parts from. Always need those low ohm fusible resistors, or a diode.

[@luvradios]

@@zulumax1 That's awesome man, such a cool radio!