Electronics > Repair
Permanent CC and no output [Longwei K3010D]
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xavier60:

--- Quote from: czesio666 on November 19, 2019, 12:47:31 pm ---U1 supply correct 12V

Current pot set to max:
U1-A #2    0.18V
U1-A #3    0V
U1-A #1     10.7V


0.12V drop on R4
Q1 open, 0.63V on BE, negative 6.4V CE

--- End quote ---
With 0.18V on pin 2, pin 1 should be saturated negative.
xavier60:
Does U1 have a negative rail?
czesio666:
Yes, the same thing is on U1-B.
U1-C and U1-D seems to be ok.

Ok, so I will replace TL084BC (LM324 is on schematic).

U1 Vcc+ is 12V, Vcc- is 0.8V. Something wrong with supply?
xavier60:

--- Quote from: czesio666 on November 19, 2019, 01:06:43 pm ---Yes, the same thing is on U1-B.
U1-C and U1-D seems to be ok.

Ok, so I will replace TL048BC (LM324 is on schematic).

U1 Vcc+ is 12V, Vcc- is 0.8V. Something wrong with supply?

--- End quote ---
You will need to trace it, the schematic isn't clear about what supplies negative rail to U1.
Chris56000:
Hi!

The Chinese might be good at designing cheap electronics (& counterfeiting it as well!!!) but their diagram & documentation skills are bloody atrocious!!

The Op Amp Negative Supply is provided by D6 (SR1100), with reservoir capacitor C14 (100uF), with decoupling filter R30, the –12V for the op–amps @ pin 4 is across C8 at the junction of C8, R01 (2M2) and R30 (4R7) – this can be inferred from the low value of the –12V line decoupling–filter resistor!)

I've got some nice Drawing Office Lettering now, so I'll get started on a new drawing in due course!

Chris Williams
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