I haven’t replaced any resistors, but I will check them to be sure.Also, from my notes on the 880, R255/256 and R261/262 could be incorrect on the schematic. I've found those to be 390Ω and 120Ω instead of the marked 330Ω and 82Ω. If those were replaced as part of the rebuilding of the board, check those.
Well Watthour, you taught me a huge lesson with your questions. I cannot thank you enough! I was bound and determined that my problem had to be an active component. However, I had gone in and logged every voltage for the transistors you asked about, and then I went to measure the four resistors, and guess what? The resistors were all open...all four of them. So is the 390 and 120 correct, or should I use 330 and 82? I temporarily solderd in 330 and 150 (I missed your note and saw 150 ohms marked on the circuit board layout in the service manual). It fired right up, and the protection relay pulled in. I obviously want to get the right values in there and then adjust the VRs for offset and bias.Also, from my notes on the 880, R255/256 and R261/262 could be incorrect on the schematic. I've found those to be 390Ω and 120Ω instead of the marked 330Ω and 82Ω. If those were replaced as part of the rebuilding of the board, check those.
Okay...well therein most likely lies the problem. Again, I'm a newbie and you can't believe everything you read on the internet. I saw some posts somewhere along the way (may not have been AK) that made it sound as if it would actually be better to raise the capacitance of the main filter caps. Based on that, I've been bumping them up more than the 10-15% increase you mentioned. I have been bumping them up to something the same diameter, which in this case went from the original 15000 to 22000. Based on your last post, I'm going to bet that extra capacitance is more than the transformer can take. I'll need to order a different set and figure out how to deal with the size difference.Yes, draining the main PS caps can dim the lamps. Smaller amps do that more noticeably, but even larger amps can exhibit that. I have 450s and 550s that do that very noticeably, and even the 850/950 will dim a bit when driving 4Ω at elevated power levels.
Bumping the capacitance of the main filters might alleviate that a bit, but the transformer size (kVA) and main rectifiers must also be up to the task, so usually a 10-15% increase in capacitance is relatively safe for the power supply, but not always without consequences.
Well these LED lamps are dimming a lot more than would be acceptable by any consumer. I'll check the transformer temp. When I put the LEDs in, I added a bridge rectifier to do away with the 60 cycle blink. Any ideas on how to deal with this problem? Is there anything else I might need to look at to make sure everything is okay, and not some issue that's causing them to dim? I would think that if the incandescent bulbs were still in there, they would be dimming significantly as well. Do I maybe need to come up with a different place to pull power for them?If the transformer does not get inordinately hot (above 150°F) and the main rectifiers remain below that same range, don't lose any sleep over it. I've done the same kind of thing, but be aware that in some cases, there is such a thing as too much.
No, that was my first thought too, so I checked it and it’s a standard unit set up for 120V.Regarding the voltages, is this a multi-volt unit (Type S/G)? If so, the voltage selector plug might be checked. Utilities seem to be running their line voltages closer to 250V on residential feeders these days, at least in the U.S. that can affect some of these older "117V" rated devices.
Okay, thanks. I just needed a sanity check on thatAt design conditions in the S-S/G model shows ±44.5V on the main supply. Your measurements seem reasonably close.
The SX-880 that I'm working on has nice crisp highs, and the lows are there, but not nearly as pronounced as even the SX-737. I'm wondering if this is normal for the SX-880, or if mine needs some further work in the preamp area possibly?
Watthour,Generally speaking, the 20/30 series had what some classify as a "warmer" sound with more tonal coloring. Some attribute it to slower components or circuit designs rapidly rolling the highs off into softer tones. The 50 series typically had a little less "color" in the sound and a bit more even reproduction. The 80 series was the more "clinical" or "technical" sound, reproducing whatever was input in it's truest possible form. It's been discussed several hundred times here, usually ad nauseam, and with much opinion and speculation. There are several RC networks in these amps, some intentional, and some probably unintentional, which affect what frequencies are passed through and resonance.
A few things on the 80 series which might affect the apparent lack of lower frequency power are the power supplies, the quality and design of components in the audio path, the reliability of connections in the circuits in things like the high/low filter switches, pot wipers, and other signal path switches, and the speed of the amplification and output devices (and their damping). Non-inductive resistors might sound different that plan wirewounds, faster switching transistors may be less likely to roll the sustain the lower frequencies and roll off the higher frequencies. Rolled foil e-caps may resonate a little more than stacked films. And on, and on.