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Peavey xr-684

JohnDio

Jul 30, 2022
3
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Jul 30, 2022
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hi everyone. new to this forum. been in the electronics field on and off since the mid 60’s and always learning :)
i’ll tackle almost any electronic device with good outcome.
i’ve been reading some old posts about the 684 with sound advice from some seasoned tech’s.

my present repair is my own xr-684.
it started to need multiple on & off cycles to finally power it up and would work fine till the next time i applied power.
after about 8 months of moderate use (2-4 times a week), it finally failed to power up. removed amp pcb to t/s. regulators were very low outputs.
final heat sink close to power supply got hot so, i shut it down. so as to not blow any finals, i removed them. reapplied power. still low voltage on both reg’s so i removed the 4 ic’s ion the board. regulators came up to normal. i find ghat plugging the ic’s back in creats load on the regulators again.
I’ll resume bench tests this coming week.
- john
 

73's de Edd

Aug 21, 2015
3,613
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Aug 21, 2015
Messages
3,613
Sir JohnDio . . . . .
O.K. . . . . .so I go thru pages 12-28 of defined audio processing stages of the 684 unit . . . .. but with them giving NO trace of a power supply, until the last page where the base power seems to be coming from + and - 15 V supply lines.
Where is tech / schema info on this power supply ? ? ? ? ( part of separate amp ? amp part # ? )
As, your sometimes "iffy " powering up situation seems to relate to these +15-15 supplies coming from another unit , using switch mode supply design, that has eventually deteriorated with time and use and is now in a critical working situation / stage of not initially starting up for you . . . . without several "kick start " attempts.
Usually this is related to power supply E-caps deteriorating to the threshold of a "iffy" start up / working state.
 

JohnDio

Jul 30, 2022
3
Joined
Jul 30, 2022
Messages
3
Hello Edd,
Thank you for your response.
I did a little T/S this morning before other bench repairs. With all 8 finals removed and u101 & u201 removed, + & - regulators are at 15 to 16vdc with no ripple and run warm on the heat sink, not hot. plugging u101 & 201 back in then power up, the positive rail collapses to 3vdc after r267. With that, Q109 & Q209 get hot to the touch with u101 & 201 in. Remove the opamps and Q109 & Q209 are warm, not hot.
I’ll resume on Wed (7/3) or Thurs (7/4).
- John
 

JohnDio

Jul 30, 2022
3
Joined
Jul 30, 2022
Messages
3
a quick update: i built a test circuit on a solderless breadboard to test the programmable opamps. u101 didn’t pass! it yanked down both rails. waiting for a replacement.

from what i can see at this point is that audio is being stopped by the “X”circuit. will investigate that area next.
————

“ May you live as long as you want,
And never want as long as you live“: Bud Abbott
 
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