• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Short circuit connecting preamp with amp (RCA)

elgrillo said:
Ok back again with a new multimeter.

I tooked the meshures in both brown wires , with the black/white and white wires conected but NOT grounded. Also I disconected one green wire so the bulbs dont light.

Meshurment in brown wires: 29.7V (ac) and 29.6V (ac) .

Now the DDM is autorange so no mess up with ranges anymore!

So this is good? or just spend money to know that its faulty?

Thx!
Click to expand...

With the new DMM , the ac outlet mesures 228V .
The amp is wired for 240V operation.
 
transformer is looking good .
put the brown wires back and measure the + - 41v again .
pins 8 negative rail -41v and 3 positive rail +41v. rectifier relay board .
 
petehall347 said:
transformer is looking good .
put the brown wires back and measure the + - 41v again .
pins 8 negative rail -41v and 3 positive rail +41v. rectifier relay board .
Click to expand...

Ok , with dim bulb tester between , everything conected. ( with the white/black and white wires together but not grounded)

Pin 3 gives: 10.5V

Pin 8 gives: -10.6V

Dim bulb tester lights up very bright.

Is this good?
 
no its not good ..
disconnect pins 1 and 12 on the amp board then retest voltages .
this will see if the main capacitors or going short .
if the voltage is still low measure voltage at q301 base .
i take it the relay doesn't click ?
another thing to try is lift cr302 and cr303 and recheck voltages .
 
Last edited:
petehall347 said:
no its not good ..
disconnect pins 1 and 12 on the amp board then retest voltages .
this will see if the main capacitors or going short .
if the voltage is still low measure voltage at q301 base .
i take it the relay doesn't click ?
Click to expand...

Ok peter, i disconected the wires from the filter caps as you said, and tested throw the dim bulb test.

39.1V in boths pins . The dim bulb tester dimmed and the relay energized.

BTW one of the screws of one of the filter caps came out fine but problems to get in again. The filter caps are realy old so if thats the problem I would change them for new ones. I tHink thry are around $16 each in mouser.

Gonzalo
 
elgrillo said:
Ok peter, i disconected the wires from the filter caps as you said, and tested throw the dim bulb test.

39.1V in boths pins . The dim bulb tester dimmed and the relay energized.

BTW one of the screws of one of the filter caps came out fine but problems to get in again. The filter caps are realy old so if thats the problem I would change them for new ones. I tHink thry are around $16 each in mouser.

Gonzalo
Click to expand...

BTW The only wires I left conected to the filter caps were the ones that goes to the relay board.
 
ok filters are good and relay circuit seems to be behaving .
wire amp boards back in and check voltage at pins 1 and 16 relay board .
be aware the filters will be charged up and should be bled off with a resistor . test the voltage across each one .
 
petehall347 said:
ok filters are good and relay circuit seems to be behaving .
wire amp boards back in and check voltage at pins 1 and 16 relay board .
be aware the filters will be charged up and should be bled off with a resistor . test the voltage across each one .
Click to expand...

Ok Peter, in pin #1 i have 79mV and in pin #16 I have 9.7V.

O voltage across Filter caps ( or maybe I'm doing something wrong) And I didnt discharge them with a bleeder resistor. I think maybe they r too old.

Thx
 
elgrillo said:
Ok Peter, in pin #1 i have 79mV and in pin #16 I have 9.7V.

O voltage across Filter caps ( or maybe I'm doing something wrong) And I didnt discharge them with a bleeder resistor. I think maybe they r too old.

Thx
Click to expand...

So I can guess that the problem comes from the board that is connected to pin#16 (9.7V) that is too much current? Maybe a blown transistor or resistor ?
 
yes the 7.6v is putting it in protection this is why the relay wont click and the voltage is low .
ok we have narrowed it down to the right hand channel . there are some transistor and resistors to check .
q201
q202

zener diodes
cr201
cr202
and resistors
r202 r204
r203 trimmer

also
q1
q2
q206 to q210
cr203
 
Last edited:
petehall347 said:
yes the 7.6v is putting it in protection this is why the relay wont click and the voltage is low .
ok we have narrowed it down to the right hand channel . there are some transistor and resistors to check .
q201
q202

zener diodes
cr201
cr202
and resistors
r202 r204
r203 trimmer

also
q1
q2
q206 to q210
cr203
Click to expand...
Hey Peter thanks a lot, When I finish testing that components I will post the updates.

Thanks a lot for your time and patience!
 
petehall347 said:
i am thinking the outputs q1 q2 might be shorted or open .
Click to expand...

Ok Peter.

I think this are bad news...

Q1 and Q2 - they are fine :D

Q209 and Q210 - bad. :thumbsdn:

Q208 - Good

Q206 - Bad

Q207 - Bad

R203 - good

R202 and R204 - good ( both 7.5k resistors ( there is an error in the list))

Cr 201, cr202, and cr203 : I dont know how to mesure them properly.
 
I have replacements for q208 (ss47) that is mje182. and for q206 (ss48) that is mje172.

also I can get q207 that is a mpsa20.

But problems with q209and q210, no information for this ones.

Any help?
 
this is data for the one that's fitted
2N4037
TRANSISTOR NF/S, 60V, 1A, 1W, >60MHz
that must have worked before .
2n3053 should pair with it .
these are available and cheap price
 
i cant find data for the originals .. supply voltages are 41v . so we are looking for double that to be on the safe side . 60v i would think ok though .
will research some more later
 
You must log in or register to reply here.
Back
Top Bottom