Friend of mine comes over today with this old school stereo receiver with a blown right channel. Barely any output at full volume, mostly all severe distortion, crackling, etc. Left channel is fine.
I normally wouldn't mess with but he says it was his Dad's, used it in the garage for years and years while they both worked on cars, etc.etc.etc. Ok. Fine. Friend of mine. I'll take a look-see.
-Thou shalt check all voltages.
--And thy voltages checked well.
-Thou shalt look for rotten solder joints.
--And said solder joints AND wire wrap joints look well and fine. Or at least as fine as a 20+ year old piece of dusty stereo can be.
So, the output amp is an ECG1331. Can't find any real decent data on it, but it crosses over to a NTE1331, and a suitable sub's are STK461, STK463, STK465. Same type of thing with different wattage and voltage ratings I assume.
Found a couple datasheets for the STK463 with some internal diagrams, and a generic power amp schematic for it...
http://pdf.datasheetcatalog.com/datasheets/1150/499377_DS.pdfand
http://pdf.datasheetcatalog.com/datasheets/37/499379_DS.pdfHere's my voltage readings with it on, warmed up, operating, balance centered, low volume, music out the left side, nothing out the right side: (Interesting differences highlighted)
Left Channel - OK
1- Left Ch In -.07VDC
2- Left Ch Fdbk -.075VDC
3-GND
4-Left Channel BIAS -1.3VDC (.3VAC component)5- -30VDC
6- Left Ch Fdbk 2 - 0VDC (.3VAC component)7- Left Ch Output - .25VAC8- +28VDC
Right Channel - Nothing (pinout mirrored image of left channel)
16- Right Ch In -0VDC
15- Right Ch Fdbk -.55VDC
14- GND
13- Right Channel BIAS +14.9VDC12- -29.75VDC
11- Right Ch Fdbk2 +.68VDC10- Rt Ch Output +.68VDC9- +29.25VDC
From looking at the internals of the amp (
http://pdf.datasheetcatalog.com/datasheets/1150/499377_DS.pdf),
I shouldn't have +14.9VDC on pin13, as it's tied to the base of what looks like a Darlington pair, but that section doesn't look like it's the actual driver. Nonetheless, I think that voltage on pin 13 (right channel) should be ~1.3V like pin 4 (left channel) since it runs up to the base of that transistor pair.
Replacement part off of ebay will run me about $17. Cheap enough.
Judging from the condition of the speaker wire the receiver was attached to, it's entirely possible that the right channel wires shorted together and took out the amp...but I'm not going to jump to conclusions just yet.
Any thoughts from the masses...