my attic sx-3800 repair

Someone please help this lad out. Please?

Give it a moment, perhaps Markthefixer, Mattsd, or Echowars will chime in soon.
 
8golftango said:
cant find that 1/2 watt 2.2ohm resistor with flameproof? just use a regular one ok?
Click to expand...
which resistors are you referring to ? board numbers ?
why do you want to change them all ?
i use a metal film . they don't burn with a flame. best to know which ones you refer to to be sure ..
 
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This is on the power supply board (gwr122b) resistor r222. A 2.2 ohm 1/2 watt resistor that also functions as a fail safe. I read that mtf admitted that these were not available in flameproof from mouser, but was unsure if the regular resistor would work as well. I know he gave a part number for one from mouser that wasnt flameproof
 
ok well power supply board is rebuilt. final transistors tested ok, new thermal compound and modified heatsink to keep new final trans plugs from bending
 
I love what you did with the heat sink ... ! Might steal the idea from you with my SXD7000 which is in my restoration list for the coming year.
Which thermal compound you used?
Bumpin' for ya'
 
If u do be VERY gentle while drilling and tapping the aluminum heatsink. Especially where your drill bit will exit on the other side. I wasn't as careful as I should have been and bent some of the fins a bit, as u can see in that last pic. Also im not sure it was completely necessary to have the connectors clamped down BUT I got it into my head that I was going to do it. haha :D thermal compound was ceramique 2 by artic silver i.e. radio shack
 
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I have replaced some components on the amp board, the dual emitter resistors, all electrolytics, and the problematic transistors that mtf recommends. Tested the op trans with echowars method and they all seem good. I havent messed with the transistors on the little heatsinks. Those are the drivers right?
 
interesting physical capture of the phoenix sockets... :D

omri, the risk / reward / necessity ratio tilts away from needing to capture the sockets.
Looks nice, but the other connectors lasted pretty well, it's not their fault the material used to make them did not stand the test of time.

yup, those are the drivers. Make sure the dual idle pots are all turned DOWN.

BTW, when all components are operating correctly, the offset can be adjusted with the output transistor sockets disconnected, the amp will DC balance - but NO LOADS, NOT EVEN HEADPHONES. This will actually substitute for the DBT - the DBT only saves the output transistors anyway...

:yikes: MAKE ABSOLUTELY SURE the POWER IS OFF AND THE MAIN CAPS ARE DISCHARGED BEFORE plugging the sockets into the output transistors. :yikes:
 
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Hi Mark! Yes i agree as far as that goes, if i had to do if again i would probably not do it or at least do it differently. The connecors arent exactly clamped down, there is about a 1/16" clearance.
Yez i plan on setting idle and bias with op trans disconnected. Everything is back together. Replaced my bent power switch, replaced a broken tape switch. Removed the front panel and deoxit all the pots underneath it. Wow took me a couple hours to get the front panel back on and two forceps and hemostats!!! Deoxited the tape switches and speaker selectors and input switches at the back.
 
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You CANNOT set idle without the outputs in place. IDLE goes THROUGH the outputs.

Only the offset can be set like that, to get the unit out of any DC protection because of the initial unknown offset pot settings and make it easier to be sure it is safe to connect the outputs.
 
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Hmm ok. I keep getting confused by different manufacturers terminology. Some call it dc offset and some bias. But we are talking about the idle lol! Thanks so much!!
 
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Question: anyone have any of thoae weird nuts that go on the volume and bass knob that keep the front panel clamped down? I actually have one but is cracked in the middle and im afraid it will cause problems
 
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