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Chuck <ch@dejanews.net>: Jun 28 12:46PM -0500 On Wed, 27 Jun 2018 15:43:58 -0700 (PDT), captainvideo462009@gmail.com wrote:   >parallel but it's so crowded in that area you can't see anything. I Really appreciate any help. Lenny   >Chuck >I put a remote near the antenna and it does respond to AM. I did see it respond to FM at one point too. But then it didn't seem to after awhile. The thing is I can't find VR2 that you mentioned. Which meter is the signal meter? Lenny Lenny, M705. I wonder if the the meter movement is sticky?

captainvideo462009@gmail.com: Jun 28 02:11PM -0700 > This is my own receiver. Last year it started taking longer and longer for the protection relay to activate and turn on the speakers I finally took it out of service. I recall that it had no other problems that were evident. I had posted this problem at that time and I think that it was Chuck up in Canada who nailed it immediately. He recommended changing C6 on the protection board and .that resolved the protect relay problem. Now however there is another problem that I never had before. Most of the dial lights including the signal meter light are out and that meter also seems to be inoperative as well. I never had any trouble with any lighting or the signal meter on this receiver. This is a big quadrophonic receiver. The switching is done through the main selector switch and it's a nightmare to get to. A real rats nest. Does anyone who has worked on these recall any common problems with lighting on one of these? I suspect a ground problem because so many of these lamps are in parallel but it's so crowded in that area you can't see anything. I Really appreciate any help. Lenny   Chuck I'm embarrassed to say that I think I know what happened. The RF section on this receiver is pretty hot and so for servicing it on my bench I didn't bother connecting the old outside VHF/FM antenna that is now used just for FM, throughout our house. I was getting what I thought was a decent signal in my basement with just a short piece of wire connected to the high side of the 300 ohm terminals. Apparently in spite of the fact that the FM stations I was tuning in sounded OK there must be a signal threshold that must be met before the signal meter will move. With the unit connected to the outside antenna the signal; meter is now working fine. I don't think that there was ever a problem with it. It was more aptly due to "operator head space"   So now I'm at the final stage of this repair. I have owned this receiver for over thirty years now. I originally bought it from the junk man at our town dump who was going to strip it, for 5.00 It has been a great receiver for all this time,however the 4 channel circuitry never seemed to work properly on it. I worked on it, John Del, also a contributor to this thread worked on it as well, but we never seemed to be able to resolve it. So for that time I have lived with it.   A few weeks ago I was browsing Craig's List and found a guy about 30 miles from my house who had one of these for sale. I went out, and looked at it and thought it might need a discriminator alignment, and I picked it up for parts. So today, first I swapped out the 2048 board. I now have output on all 4 channel positions except the first and last, which seems like it should be. I have 4 speakers connected to speaker A front and back terminals. It seems to sound "OK:" but I can hear a very slight "popping" way down in the mud in the rear speakers.   So I was going to swap out the 2047 board, however in spite of the fact that it would fit in the same slot as my original, the board from the donor receiver is totally different. For one thing there are 7 potentiometers on the donor board and only three on my original board. There are also two 8 pin chips on the original board but it seems to be all discrete components on the donor board. So for boards that fit into the same positions in the chassis are these boards forward and backward compatible? After all this I would hate to make a swap and because it was incompatible wind up destroying something. Lenny

Chuck <ch@dejanews.net>: Jun 29 11:06AM -0500 On Thu, 28 Jun 2018 14:11:48 -0700 (PDT), captainvideo462009@gmail.com wrote:   >backward compatible? After all this I would hate to make a swap and >because it was incompatible wind up destroying something. >Lenny Lenny, The board compatibility question I can't answer. Back in the day we never switched out whole boards on Sansuis. Always troubleshot to the component level. Sorry. Chuck

Miguel Teixeira <geotexmig@gmail.com>: Jun 29 07:07AM -0700 Hi, I´m a doing a historical research on a Spectra Physics Laser model nº136, produced in U.S. in 1960´s/70´s: https://imgur.com/a/zRSXMFE   I'm really interested in details related to production of this model and his catalogue. I just found this one: https://www.repairfaq.org/sam/brochures/SPOHLC1975/index.html but probably there are more specific documents.   I appreciate all information that you might share about this device Thank you, Miguel

bruce2bowser@gmail.com: Jun 28 08:37PM -0700 On 2018-06-27 22:33:46 +0000, Your Name said:     > The author's basic conclusion is yes, HDR does shorten the life of an > OLED TV quite considerably (his rough calculation out it as going from > 100,000 hours down to 25,000 hours).   You have to wonder where the already-shorted-out TVs are, for example.

"Gareth Magennis" <soundserviceleeds@outlook.com>: Jun 28 08:45PM +0100 Hi,   this is the amp schematic:   http://tinypic.com/r/wlxjrm/9   The amplifier works normally, except on Power up and Power down, there is a huge low frequency DC offset going on which sounds and is very alarming. Here's a scope capture. http://tinypic.com/r/5pjslw/9   The bottom blue trace is the Mute signal at the base of Q30. The Yellow trace is the power amp output, at 20v per division, so pretty much full swing.   All these traces are without any load, but it does pretty much the same thing with a load.   The first mute signal positive is at switch on, the second is at switch off. Horizontal sweep is one second per division, so what you see is turn on, wait 4 seconds, then turn off. There is a sine wave running through the input, which you can see after both mutes unmute, (the fat lines below the zero point), showing the amp is indeed muting and passing the signal when it should.   If you disable the mute signal by shorting C151, thus connecting Q30's gate to ground and turning it on constantly, you get the following trace. http://tinypic.com/r/4szokx/9   There is a switch on spike, but no long drawn out DC stuff going on any more, which leads me to suspect the muting is causing this to happen. As you can see by the fat line, the signal is now passed immediately at switch on, as the mute is now disabled.     I can't find anything obviously wrong, and the amp works normally except for the huge anomalies at switch on and off. The negative feedback seems to be in circuit, the Power supplies are all normal and power up immediately.   I changed Q30 for good measure, no different.   This is mostly SMD stuff, so not that quick and easy to whip stuff off and on again for testing.     Amplifiers are not my most favourite circuit, and I don't know a lot about how DC offsets are managed in them, but it seems this one definitely has a problem managing the DC.         Cheers,     Gareth.

Phil Allison <pallison49@gmail.com>: Jun 28 05:29PM -0700 Gareth Magennis wrote:   > Amplifiers are not my most favourite circuit, and I don't know a lot about > how DC offsets are managed in them, but it seems this one definitely has a > problem managing the DC.   ** SRM450 is the model number of a Mackie powered loudspeaker, the schem is for the amplifier module that drives the 12inch woofer.   Thing to note is that such units undergo frightening amounts of vibration plus the occasional impact with the floor - which can put cracks in the PCB and or loosen components that are not extraordinarily well held down.   No amount of perusing and pondering over a schem will find any of that.   Nevertheless, the muting system is a common one in that the front end of the amplifier is starved of current so it can no longer drive the following class A stage and hence the output stage. Q30 does this by disabling Q29 & Q31 and hence both input diff pairs ( Qs 25 thru 28)   So, one needs to engage the mute circuit ( apply +10 or more to Q30's base) and see why that is NOT happening correctly. The amplifier circuitry is symmetrical so look for a voltage that is not reflected on the opposite side in mute mode.       .... Phil

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