Luxman LV-105 static on on channel

[JeffInTampa]

Hi all,
I have an LV-105 purchased new in the 80's that has just developed a hiss and crackling on the right channel. This appears on both sets of speakers, and is independent of both volume and balance settings, and the input. A bad trace is unlikely since the static also appears independent of temperature. A cold-solder is a possibility, but I'm hoping this is just one of the tubes, which of course have been pre-heating for about 27 years.

Any suggestions?

If a more complicated repair is indicated, I have the tools and skills (from building TTL test fixtures) but with my travel schedule it would end up being yet another uncompleted project. In that case I'd appreciate any suggestions on repair shops in the Tampa/St. Pete area.

Thanks!

 

[TonyTecson]

you can do the shotgun approach, open the bottom cover and touch up the solder points using good quality solder and a clean tip iron......

you can clean the underside of the board with isopropyl alcohol using cotton swabs, then with a magnifying glass you can look for cold solder joints, they manifest themselves as those appear to be broken/cracked....

 

[Cassiel]

but I'm hoping this is just one of the tubes,

Most likely the cause of the problem. Start there.

 

[TonyTecson]

the 6CG7 tube was used as differential VAS, preceding the jfet input ltp and driving a pnp common emitter driver stage to the lateral output mosfets.....i doubt that it is the tubes....

cold solder is the more likely culprit...since the crackling sounds does not trigger the output relay off....

 

[Cassiel]

Right. I thought it had a tube output stage.

 

[TonyTecson]

the 6CG7 tube was used as differential VAS, preceding the jfet input ltp and driving a pnp common emitter driver stage to the lateral output mosfets.....i doubt that it is the tubes....

cold solder is the more likely culprit...since the crackling sounds does not trigger the output relay off....

my bad, the pnp trannie is actually a common collector.....

 

[JeffInTampa]

Thanks, all! I was thinking of swapping the tubes and if the static moved that would isolate the problem. But it sounds like I have an afternoon or two with the iron and solder sucker in my future.

I assume the board was wave soldered, but there are probably some connections that were done manually during final assembly, and those would be most suspect. Are there any downloadable diagrams that might show these?

Finally, should I switch to lead-free solder or stick with the old stuff?

 

[DavesNotHere]

If the phase splitter tube malfunctions or an unmatched section tube(regular tube) is installed, it will cause kinda off channel FM static sound. also if the tubes are handled/stored incorrectly it can cause a similar noise (shock noise) due to damage to the mechanical structure inside the tube)

 

[TonyTecson]

Thanks, all! I was thinking of swapping the tubes and if the static moved that would isolate the problem. But it sounds like I have an afternoon or two with the iron and solder sucker in my future.

I assume the board was wave soldered, but there are probably some connections that were done manually during final assembly, and those would be most suspect. Are there any downloadable diagrams that might show these?

Finally, should I switch to lead-free solder or stick with the old stuff?

i've repaired many Japanese amps, and these problems of cracked/loose solders are not uncommon....

here we go:
Luxman LV-105 Service Manual free download,schematics,datasheets,eeprom bins,pcb,repair info for test equipment and electronics
Luxman LV-105U Service Manual free download,schematics,datasheets,eeprom bins,pcb,repair info for test equipment and electronics

pdf: Luxman LV-105 Service Manual free download,schematics,datasheets,eeprom bins,pcb,repair info for test equipment and electronics

 

[JeffInTampa]

Thanks, Dave & Tony!

I'm experienced in handling tubes. If I remember correctly, the 6CG7 tubes are a matched pair and must be reaplaced together, but they're probably OK.

I downloaded both sets of manuals. I noticed the "U" manual is more complete as it has all the daughter boards. I'm not sure how the LV-105U differs from the LV-105, but if it is anything critical please advise.

With a houseful of family for the next week this will have to wait. If it gets cold enough to use the fireplace nobody will notice the cracklin' in the carols anyway...

Merry Christmas, all!