My first post with substance (hopefully). If you wanna skip the back story go to "XXXXXXXXX" below. about me I am not an EE or a lifetime electronics guy. I am however a Civil engineer and a lifetime audiophile. About 1.5 yrs ago My Meridian G68 made the magic smoke from the power supply. I knew I didn't have the money to replace the unit outright so, decided to learn and repair it myself..... and so it starts. Quite a benchful of test gear and self learning later here I am. I did manage to install a linear power supply to the Meridian and recap all the rest of my gear and happily all running again. When I look at my bench full of gear I probably could have purchased a new unit and then some but what fun would that be. So I decided to check out some of the gear from my youth that I lusted after and could never have. So first e-bay purchase a Pioneer SX-3800, next a Marantz 2265B, and bought locally (i live in Germany) a Technics SA-600. The SX-3800 arrived first so it is on the chopping block right now-- looking back maybe should have started with one of the others but I'm waste deep in it now.
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SX-3800
I have been reading and learning from this forum and know ya'll appreciate the "how did you get there" part of a restoration. here goes:
The unit was powered up in the e-bay photos and was described as having "no Sound". looking ai saw that the back jumpers were not installed , I figured maybe somebody just doesn't know about that and I may get lucky.
SO when it arrived I powered it up (knowing somebody recently did and I used my BK 1653 to bring it up slowly and limit current). Good news nothing blew up (yet). All functions seemed to be intact. so hooked up dummy load, Oscilliscope , Keithly 2015 to check initial operation. DC offset was R = -2.8mv, L=8.7mV (not Teabag, i thought). Started dinking around with a 1K HZ, 150 mV input -- THD wasn't to bad from pre amp section. so ran it through amp section one weak channel -- then got the smoke. I QUickly shut down.. I wasn't all that concerned since my plan was overhaul but didn't powerit up anymore and immersed myself in disassempling and cleaning (lots of pics for my reference for reassbly) SOrry so long folks I'll get to the point. WIth what I read on here and the great tips and advise I tackle the power supply board first. Tested ALL components with legs lifted or removed from circuit. RE-capped, Re-diode, Re-transistered the whole board with info learned from this forum (Thank You!)
Now I'm working on the Amp Board (GWH 139-A) got the capps OK but I didn't find a transistor list. I pieced together info for 6 transistors in the middle of the board and 8 diodes but could use some help figuring the others specifically:
Q102,Q101 - C1775
Q110,Q105 - C1915
Q122,Q121 - A904
Q124, Q123 - C1914
Q115, Q116 - A905
Q111,Q112 - A750
Q113, Q114 - C1400
Q117, Q118 - A750
Q125, Q126 - C2275
Q127, Q128 - A985 (A1011 was what was installed) (drivers - hfe really varies between the two sides)
Sorry so long winded. I haven't tested any of the rework yet (I know this is a mistake but the thing was SOOO grungy and I knew I was going through it all) so it is all disassembled. Plus I like working on one board at a time on the bench with wrestling with the whole unit.
BTW - I desoldered the pin headers with wires attached thinking it would keep things in order - Wrong ! many of the plastic holders just disintegrated. I tried looking pin headers up and can find many but they specify Pitch (which I think id the pin dia.) but I don't see in the specs pin spacing-- most of what I measure is about 5mm except the header from the transformer which is about 9-10mm spacing -- is the spacing standard?
Thanks so much for your help already and look forward to the future! Hope I did this right......
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
SX-3800
I have been reading and learning from this forum and know ya'll appreciate the "how did you get there" part of a restoration. here goes:
The unit was powered up in the e-bay photos and was described as having "no Sound". looking ai saw that the back jumpers were not installed , I figured maybe somebody just doesn't know about that and I may get lucky.
SO when it arrived I powered it up (knowing somebody recently did and I used my BK 1653 to bring it up slowly and limit current). Good news nothing blew up (yet). All functions seemed to be intact. so hooked up dummy load, Oscilliscope , Keithly 2015 to check initial operation. DC offset was R = -2.8mv, L=8.7mV (not Teabag, i thought). Started dinking around with a 1K HZ, 150 mV input -- THD wasn't to bad from pre amp section. so ran it through amp section one weak channel -- then got the smoke. I QUickly shut down.. I wasn't all that concerned since my plan was overhaul but didn't powerit up anymore and immersed myself in disassempling and cleaning (lots of pics for my reference for reassbly) SOrry so long folks I'll get to the point. WIth what I read on here and the great tips and advise I tackle the power supply board first. Tested ALL components with legs lifted or removed from circuit. RE-capped, Re-diode, Re-transistered the whole board with info learned from this forum (Thank You!)
Now I'm working on the Amp Board (GWH 139-A) got the capps OK but I didn't find a transistor list. I pieced together info for 6 transistors in the middle of the board and 8 diodes but could use some help figuring the others specifically:
Q102,Q101 - C1775
Q110,Q105 - C1915
Q122,Q121 - A904
Q124, Q123 - C1914
Q115, Q116 - A905
Q111,Q112 - A750
Q113, Q114 - C1400
Q117, Q118 - A750
Q125, Q126 - C2275
Q127, Q128 - A985 (A1011 was what was installed) (drivers - hfe really varies between the two sides)
Sorry so long winded. I haven't tested any of the rework yet (I know this is a mistake but the thing was SOOO grungy and I knew I was going through it all) so it is all disassembled. Plus I like working on one board at a time on the bench with wrestling with the whole unit.
BTW - I desoldered the pin headers with wires attached thinking it would keep things in order - Wrong ! many of the plastic holders just disintegrated. I tried looking pin headers up and can find many but they specify Pitch (which I think id the pin dia.) but I don't see in the specs pin spacing-- most of what I measure is about 5mm except the header from the transformer which is about 9-10mm spacing -- is the spacing standard?
Thanks so much for your help already and look forward to the future! Hope I did this right......