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N_Cook <diverse@tcp.co.uk>: Dec 09 03:16PM 2 topcode XG marked FETs? on the board, both with 21.7V on and other pins reasonable looking DC on them, one with corrossion around. No mention of phantom power in the user manual, I wonder what that is doing near the input. 9.3V fed onto battery supply line. 2x JRC 14558,IC4 and IC2 that one in corrossion , the other some way away, 0,8.2V supplies and 6x 5.5V on the other pins. The corroded one power rails and only 2, pins 3 and 5 commoned at 5.5V and 4 pins with all sorts of DC and varying somewhat, in effects on or off mode. So off with that SMD and a 4558 will go in there and see what happens

John-Del <ohger1s@aol.com>: Dec 08 10:40AM -0800 An Albanian gentleman asked me to check this for him because he has lots of tape from home, and I don't have a clue about multi system VCRs. It's an Aiwa multi system VHS model HV-MX1.   It auto selects between NTSC and PAL when played back, and it has a selectable output of either.   When playing an NTSC tape, it auto selects NTSC and plays a perfect picture in color on an NTSC LCD TV via AV input. When a pre-recorded PAL tape is played, it auto selects PAL properly, but the picture on the monitor is black and white horiz bars, as if the horizontal hold was off just beyond lock. However when PAL is selected as an output (despite the monitor being NTSC), the picture appears in black and white and with a "texture" to it (like playing a component input on the composite jack).   Not sure if something is wrong with the machine or some sort of incompatibility between equipment. He said it worked years ago the last time it was tried, but that was on an RCA analog TV.

jurb6006@gmail.com: Dec 08 02:01PM -0800 It probably does not actually convert PAL to NTSC. Most likely meant to be used with a multi-system TV.   Converting PAL to NTSC is more involved than a line doubler, and you might know how expensive those things were. It is also difficult the other way around. Different scan rates and color subcarrier frequencies, and that phase shift deal in PAL that makes the tint (phase) control unnecessary.   Now, there should be cheaper convertors. There's probably a chip for that. (to the tune of "there's an app for that") Also, there are PC cards for video capture, I am sure there are PAL versions. After that, there are NTSC adapters for the video coming out of the PC. This would work. Or he could just burn a DVD and that would work as long as the software does not mark it anything other than region one. (NTSC)

Chuck <chuck@mydeja.net>: Dec 09 08:22AM -0600 On Tue, 8 Dec 2015 10:40:56 -0800 (PST), John-Del <ohger1s@aol.com> wrote:     >It auto selects between NTSC and PAL when played back, and it has a selectable output of either.   >When playing an NTSC tape, it auto selects NTSC and plays a perfect picture in color on an NTSC LCD TV via AV input. When a pre-recorded PAL tape is played, it auto selects PAL properly, but the picture on the monitor is black and white horiz bars, as if the horizontal hold was off just beyond lock. However when PAL is selected as an output (despite the monitor being NTSC), the picture appears in black and white and with a "texture" to it (like playing a component input on the composite jack).   >Not sure if something is wrong with the machine or some sort of incompatibility between equipment. He said it worked years ago the last time it was tried, but that was on an RCA analog TV.     We have 2 of these vcrs at work and they will play back PAL tapes with an NTSC output if NTSC is set as the output in the menu and if the tape is recorded in SP mode. EP recorded PAL tapes won't play back properly.   --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus

"Gareth Magennis" <sound.service@btconnect.com>: Dec 08 06:55PM This is doing my head in.   Marhall JCM 600. http://www.classictubeamps.com/schematics/Marshall/jcm600_60w.pdf     Turning the distortion channel's gain/volume/master volume combination up too high will break into oscillation (a few kHz) above a certain gain. This doesn't happen unless the pre-amp is unmuted by inserting a (shorted) jack in the input socket.   As these 3 series gain controls approach the point of oscillation, you can hear the inpending frequency that will feed back rise as the gain is increased. (i.e. before feedback, the boosted frequency is gain dependent)   (Under certain test conditions it will oscillate massively ultrasonically. It's probably best not to do that very often)     Another amp repairer has been inside this amp and has attempted to fix the problem by the looks of it. He's put small caps across some electrolytics, and there was a resistor piggy backed over the top of R4, feeding VR5. Not sure why. I haven't found any other "mods", but that's not to say there aren't any.     Anyway, I've tried to isolate various things to discount them, but am going round in circles and need some ideas my head doesn't have right now.   There's some frequency dependent positive feedback going on somewhere, but since it's a complete loop broken by muting the input, it's kind of hard to isolate anything really. (Actually the input jack mutes both the input and the signal at CN6)     Any quick hints or tips from anyone? (It's not the Prescence feedback circuit, or the valves)       Cheers,     Gareth.

N_Cook <diverse@tcp.co.uk>: Dec 08 08:15PM On 08/12/2015 18:55, Gareth Magennis wrote:   > Cheers,   > Gareth.   Missing or inadequate ground line?

"Gareth Magennis" <sound.service@btconnect.com>: Dec 08 09:11PM "N_Cook" wrote in message news:n47dkr$t7g$1@dont-email.me...   On 08/12/2015 18:55, Gareth Magennis wrote:   > Cheers,   > Gareth.   Missing or inadequate ground line?       I have investigated that to a degree.   (Typical of these amps is to have the chassis ground connected to circuit ground via 100 ohm resistor in parallel with a cap)   I've checked the grounding around the input socket and how the signal is then transported to the board with the valves on it etc. Everything appears to be OK. Nobody has fitted a non insulated jack socket or anything like that.   But yes, I suspect something like the feedback is coming via the Ground, or lack of, somewhere.       This amp HAS been messed with, however. The soldering on the footswitch jack was appalling, resulting in disabling all channel change functions, which I have now fixed. There was other work that had failed that was equally poor quality.       Thanks,     Gareth.

N_Cook <diverse@tcp.co.uk>: Dec 09 12:45PM On 08/12/2015 21:11, Gareth Magennis wrote:   > Thanks,   > Gareth.   This is the next route I'd take in. Put a dummy load with scope on the amp and run via a variac. 100% mains until oscillating, then turn down to 60% or whatever , that still maintains oscillation, then probe a 600V 1nF (if ultrasonic,higher C if lower f) cap around to see where there is a change in oscillation frequency.

Chuck <ch@dejanews.net>: Dec 08 11:45AM -0600 On Mon, 7 Dec 2015 17:21:35 +0000 (UTC), Cydrome Leader >> which also didn't allow any downward movement of the mechanism.   >Was that the type with the CD cartridge, like a trunked automotive unit? >Those things were all such garbage. No. It was a 5 disc carousel. Kenwood didn't have a design in the pipeline so they outsourced it.   --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus

Cydrome Leader <presence@MUNGEpanix.com>: Dec 08 07:52PM >>Those things were all such garbage. > No. It was a 5 disc carousel. Kenwood didn't have a design in the > pipeline so they outsourced it.   Sort of sad somebody messed up a carousel. The cartridge based changers were infuriating.   Anything that requires extensive soldering and screwing around with that medical type tape to open up, like portable tape/CD players and now cameras suck too.

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