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Marantz 2226 Restoration - Shorting under load

akadrhouse

akadrhouse

SuchaNoob
Subscriber
I've rebuilt a dozen or so units at this point, but I am still very much a noob when it comes to troubleshooting issues. I do have a scope, but my ability to use it is horrible other than testing clipping and setting bias with it.

It is my 2226 and I decided to give it an overhaul.
  • Unit worked prior to me messing with it, but didn't sound good
  • I updated all e-caps, including filter caps, most t092 TRs and some t0126 TRs known to be problematic with suggested replacements from AK folks
  • I did not update the 14V 1W zener on the power supply, nor the huge diodes, one of which can be made with a pair of 1nxxx with cathodes tied together
When I fired up with a dim bulb and variac -
  • beautiful sound at low levels, when I turned up (only to like 8 o'clock or 9), a huge dim bulb flare.
  • When DB when off, it would never clear the short until the unit was turned off
  • sometimes turning it off and back on still had the short
  • eventually, could get it to return to the state of no DB flare, but as soon as gain was increased -> flare
I talk to friend, suggested testing output TRs- they were way off
  • PNP A267 - HFE of 17 and 123
  • NPN D188 - HFE of 24 and 15
Ordered and replaced with
  • PNP MJ2-1195G - HFE at 108,108
  • NPN MJ2-1196G - HFE at 62,62
Turn on unit to test
  • Dim bulb full flare - @ zero gain - always
  • If I remove speaker load on terminals -> no Flare (no short)
I am kind of at a loss here. My first thought is that it might be a power supply diode that is wide open but I'm not sure. Anyone else had this kind of issue or have ideas? Thanks for reading!
 
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Some Marantz receivers do this type thing on a dim bulb. Wish I knew which one(s)! BUT, with speakers connected being an issue I may guess that the dc offset on the output terminals is greater than zero. Disconnect the speaker wires, leave the switch on and check.the dc voltage.
 
Well, I adjusted dc offset, adjusted power amp and power supply. And took a chance off the DBT. No issues. Clean sound. Very odd. I'm going to put it on the scope next and just see if the wave forms are clean and if where it clips.

Thanks for responding @rBuckner
 
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