Kenwood KA-3500 and my blooper

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Jump to Latest
Mooly

Mooly

Administrator
Joined 2007
Paid Member
I wish I had this on the bench in front of me.

Try it with a speaker... without a scope its as good a clue as any as to what may be going on. Keep the volume low.

No bias now and yet there was before. Only the cap has changed, we have Qe9 and 11 refitted as before.
 
Mooly

Mooly

Administrator
Joined 2007
Paid Member
Something seriously amiss with those readings. No open circuit print ? Each driver and output transistor should have approximately 0.7 volts across the base emitter junction.

So you are losing 8 volts between Re27 and the output. That should be easy to find. Just stick your meter lead on the speaker positive output and work back.

The offset itself is still at around 0.2 I take it ?
 
Mooly

Mooly

Administrator
Joined 2007
Paid Member
Don't turn it up with the bulb fitted.

So its basically working. I have serious doubts over Qe9 and 11. If they are leaky then will cause a problem. Did you test them when you took them out ? I really think they should come out and be tested (or left out for now). If they are difficult to get too then just snip the emitter lead of both to isolate them.
 
Mooly

Mooly

Administrator
Joined 2007
Paid Member
Lower Tones said:
offset at speaker terminals .186.
in from speaker, at Re49, same .186
between Re49 and Ce25 rises to .191volts. BUT on other side of Ce25, 0volts?
is this significant? take a peek at the schem. where/why does the voltage rise on the Ce25 side of Re49?
Click to expand...

One end of Ce25 goes to ground and so will have zero volts. The other end will just reflect the offset.

Listen :) You have around 0.2 volts offset as measured from ground to Re49.

Now move back one step and measure the voltage on the base of Qe21. It can not be higher than around 0.9 (your offset plus 0.7). If that's good then move back another step to the base of Qe17. Whatcha got. If you have 20 odd volts on Re19/Re27 junction you must now be seeing that on Qe17 base.

east electronics said:
I am sorry to say that amplifier repair is about procedure

I wouldn't connect a load to an amplifier that presents 200 mv offset ...

I wonder why don't you spend some time tracing the fault ...

i wouldn't also connect a load to an amplifier before i scope for signs of oscillation ( after the modifications made of that level done )

Kind regards
Sakis
Click to expand...

I know :)
 
east electronics

east electronics

Member
Joined 2006
eastelectronics.gr
I actually mean this ... i will be happy to repair your amp for free you never know shipping might be low cost

In this way we all might gain something you an amplifier and the others a drop in replacement of parts for the specific model ...

Other than that clear your head from all this quick posting , use the methods given by me and Mooly to trace the difference in the operation .... use the scopes to see for signs of instability ...

Kind regards
Sakis
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Top Bottom