Audiophonics SR-1130 Stereo - Page 1
Forum section: electronics / repair

author: Cyberdragon
author_rank: Super Contributor
timestamp: September 20, 2016, 02:15:25 am
content: $7 score at auction, a bizarre specimen...Apparently this is an extremely rare unit. I cannot find one image of it or any info. I think I found a very brief mention of it on some audiophool forum but that was it. Any manuals would be helpful as all I can tell is what each board does and some of the wires, the rest I need a schematic for.I'll try to get some pics soon, but it basically looks like a SR-1150 but with buttons instead of switches.Status:Powers onRadio works (ish)Problem Symptoms-wiring tampered with, some looms missing, now spaghettified (also taped splices)-AM tuning trouble, continuously squeals like an angry pig while trying to tune (way worse then any tube radio), will pick up strong stations though (it has a built-in antenna, but maybe it needs an external too)-audio trouble, bass distorted, right channel very distorted, some pots still dirty-tinny audio emitting from the audio amplifier board itself with no speakers connectedI tried using a signal tracer but it picked up so much noise I couldn't hear any difference in distortion (the noise distorted it anyway).A strange oddity that might be the cause is that while the two amplifier channels look basically identical from the top, on the bottom the same parts seem to be connected differently for each side (it also seems to be measuring differently, for example a 680resistor measures 678on one side but one in the same place measures 465on the other). If this is the case then some dummy replaced the parts and put them back in the wrong places because they tried to make it look the same on each side.How am I going to fix this without a schematic or board layout? I mean I could assume it's supposed to be like the other side...but we know what that did...

author: Cyberdragon
author_rank: Super Contributor
timestamp: October 01, 2016, 07:09:33 pm
content: After careful examination the function of the boards and their connections are actually etched into the ground planes. (Would have preferred a proper silkscreen) After connecting an audio source to the wiring between the boards marked "pre-amp" and "main-amp" (speaker driver) there was still nasty distortion on the right channel. Therefore the right output amp is faulty, the question is which component?

author: Cyberdragon
author_rank: Super Contributor
timestamp: October 06, 2016, 04:57:04 pm
content: Well that's quite odd. The problem appears to be some sort of non-linear distortion (as expected). So I traced it back through the stages and found that one of the transistors on the faulty side has the same signal on all three leads!How is that even possible?Shouldn't one of the leads (either collecter or emitter) go to a power bus?

author: SeanB
author_rank: Super Contributor
timestamp: October 06, 2016, 06:31:46 pm
content: Then it is shorted or really leaky, so replace it and try again. Very possible on a transistor amplifier to gave a signal on the base, and one on collector and emitter as well. the phase splitter in a class B amplifier is one such place, where you need 2 signals out with the one being inverted in phase.

author: Cyberdragon
author_rank: Super Contributor
timestamp: October 06, 2016, 08:47:11 pm
content: Quote from: SeanB on October 06, 2016, 06:31:46 pmYep, it's just the phase splitter.I think I found the real problem, it appears to be Q511(main amp input stage) is causing major distortion. I have no idea why the output is a modulated saw tooth wave, but I'm assuming thats a reference for something. It looks similar on both channals except that when feeding in a sine wave it doesn't look like sine wave modulation on the right channal, it looks like a nasty hysteresis. The saw wave gets filtered out at the next stage to a sine wave on the good channal and a pointy sine wave on the other (this is the nasty noise that comes out of the speakers).I actually got it to work for a little while by tapping the transistor, but it failed again. It's a type C374, currently looking around to see if I have one.