Hello, i have a H/K PM665vxi and i wonder why it has -400mV at power on and why it takes several hours to creep down to +-10 mV?
Thanks. If it´s a part of the design i´ll live with it, if it´s something that´s wrong and can be fixed i may just do that.
Do you have any examples of components or which circuit in this amp that could cause this?
Do you have any examples of components or which circuit in this amp that could cause this?
Your schematics has double pair of output transistors:
, the one at Elektrotanya has single pair:
Which amplifier do you have?
, the one at Elektrotanya has single pair:
Which amplifier do you have?
Standard fare for the 80's. No servo , "tired caps" are causing the startup offset.
Typically DC offset should stabilize at the speed of NFB (R433) charging C405.
No servo on this amp....
OS
(bad cap ??).
OS
Typically DC offset should stabilize at the speed of NFB (R433) charging C405.
No servo on this amp....
OS
Nope , milliseconds to stabilize is normal. The fact that it does this shows some possible immanent failure is possible
(bad cap ??).
OS
Ok, perhaps I misread the model numbers...
Edit:
Checked the Elektrotanya file - filename inidcates 665, file contents is for 655 - hence my mistake.
This way or that way, there seems to be a slow drift on voltages - in a window of hours.
If this gear would be on my desk then I would rig up a DMM tester set:
and take photos of voltages at different measurement points after startup and after stabilizing the output.
Then there would be something to compare and discuss.
So far i have replaced all caps on PCB-1 except the larger C413-C416 470uF/100V, i´ll better replace these too.
Looks like the R433 and R434 would be worth to check restistans (power off) and voltage (power on)?
How close do the transistors need to be and how long time from "power on" do your 665vxi reach 8-15mV?
Did you adjust the DC with VR401/VR402 in 8 ohm or 4 ohm mode?