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June 30, 2022, 07:16:49 AM

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Fender 112 Deluxe Plus

Started by FenderDeluxe112Plus, April 12, 2022, 04:39:01 PM

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phatt

Sorry to hear that. :(
Ok I'm gonna take a stab in the dark and asking better minds to look at this.

Look at J1,J2 & J5 as they are all interconnected to the low voltage rails via R1 & R49 as well as CR32, C54 & C55.

Now IF??? one of those switching circuits inside J1,J2 or J5 was faulty then it could cause a big DC offset. yes/no?

I've never liked those encapsulated plastic sockets as they are rather fragile inside.

My thoughts,,If the input side of C33 was lifted that would completely isolate the power amp input from any interference.

If that resolves the Buzz then I'd hunting down the offending socket,, or just replace all 3.
Phil.

g1

So you now have no significant DC on the output, and the bulb does not get any brighter with the load connected.  That is good so far.

Connect your guitar to the 'power amp in' jack.  Do you get the same distorted sound?

FenderDeluxe112Plus

Can confirm same sound with guitar plugged into power amp in, but sound is slightly quieter.

g1

Confirm that CR14 cathode (or CR13 anode) is still 0VDC with no load connected.
If so, connect load and recheck.
Also check DC volts at pin6 of U1.

FenderDeluxe112Plus

#64
-0.036vdc at cr14 cathode and cr13 anode without load.

00.22vdc on pin 6 of u1 without load

FenderDeluxe112Plus

-0.042 cr14 cathode with load
-0.044 cr13 anode with load
0.016vdc u1 pin6 with load

g1

Good so far. 
How about DC voltages for E,B,&C of Q1,Q10,Q2,Q11
Also Q8 and Q9

FenderDeluxe112Plus

Q1
B01.22
C39.22
E-00.02

Q10
B01.22
C39.20
E-00.02

Q11
B-01.19
C-39.47
E-00.05

Q2
B-01.19
C-39.44
E-00.05

All without speaker load

FenderDeluxe112Plus


Q8
E-00.03
B-00.09
C 02.92

Q9
E-00.04
B 00.02
C-02.59

g1

Double check those collector voltages for Q8 and Q9.
Where could they be getting a voltage higher than the base voltages of the outputs?
(ex. Q1 base is 1.2V, Q8 collector gets voltage from that line)

FenderDeluxe112Plus

Thanks g1. Have just double checked the dc voltages.

Q1 base 01.23 vdc
Q8 collector 03.29 vdc

Q2 base -01.20 vdc
Q9 collector -02.74 vdc



g1

According to the schematic, that is impossible.
So something funny, or we don't have a schematic match.

Check resistance from CR39 anode to Q1 base.  And resistance from CR39 cathode to Q8 collector.
Same for CR40 to Q2 and Q9.

You cannot view this attachment.


FenderDeluxe112Plus

Continuity between cr39 anode and Q1 base.
Continuity between Q8 collector and cr39 cathode.

FenderDeluxe112Plus

#73
You cannot view this attachment.

Test point pairs marked in red and green.

g1

Quote from: FenderDeluxe112Plus on May 28, 2022, 02:07:53 PMContinuity between cr39 anode and Q1 base.
Continuity between Q8 collector and cr39 cathode.
Please specify reading in ohms.  Continuity is a somewhat vague term that changes depending on model of meter.  If relying on a meter beep for continuity, it can range anywhere from zero to 200 ohms.