Ok so I have the resistors going 13 and 10 to 19.
What I THINK you want me to check next is the voltage on the 10 and 13 pin? I put the black probe to chassis and red to each board. The left side board facing from the front I get totally different numbers than the right side board. The left side board numbers are also higher.
Should I be adjusting the VRs? Which direction? CW? CCW? (please note from which direction)
I am standing by with the resistors installed and the transistors OUT and connected to the DBT.
graphic example:
imagine your thumb is pin 13, and your index finger is pin 10. The distances represent volts. The floor is -55 volts and the ceiling is +55 volts
the table top is pin 19, it should be halfway between floor and ceiling. 0.000v
hold your thumb (-0.4 ~ -0.6v) below the table and your index finger above the table (+0.4V ~ +0.6V)
Your other fingers are lightly resting on the top of the table.
VR1 raises and lowers the table, moving your hand with it. (0.000V)
VR2 increases and decreases the distance between your thumb and index finger. (The two plus and minus 0.4 ~ 0.6V )
IF VR2 is not zero ohms initially, you will hurt your hand as your thumb and finger are forced apart.
Your fingers should NOT be stretched to the floor or ceiling, but close to the table which is halfway between the floor and ceiling.
IF everything is working correctly.
STUDY the more technical stuff below carefully before acting, every line is important, do not gloss over something...
I hope I covered most possible questions in it.
First, before power is turned on, we set the positions of the VR pots on each board.
VR1 (new one 2k or 2000 ohms) is located at the side of the board and should be at the center of it's rotation (by counting turns on this multi-turn pot), it comes like this from the factory.
VR2 (new one 500 ohms) is located in the center of the board and should be set at one extreme of location (zero ohms) - and we do NOT depend upon the CW CCW direction instructions. They can get neophytes in trouble.
Instead VR2 should be set for zero ohms measured across itself, you will see that two of the three pins on it are on the same solder pad -
that counts as ONE connection.
The remaining third pin on another pad counts as the OTHER pot connection.
With power off, the dmm is set to ohms
(200 ohms range or smallest ohms range IF the DMM has different ohms ranges)
and the dmm leads are touched to the ONE pot connection(red dmm lead)
and the OTHER pot connection (black dmm lead)
at the same time,
then the pot adjustment is rotated to adjust the reading on the meter to as close to zero ohms as possible.
It doesn't matter if there is a red/black DMM lead reversal here, either way the reading is ohms.
This sets the circuit conditions for IDLE CURRENT to be minimum or zero when the output transistors are connected.
This minimum setting , results about 0.4 to 0.6 volts positive (to chassis ground) on pin 10
and -0.4 to -0.6 volts negative (to chassis ground) on pin 13 IF THINGS ARE BEHAVING THEMSELVES.
These voltages will eventually go to the output transistors and tell the output transistors what to do.
IF things are not behaving themselves, the voltages can be far far from the 0.6 volts or so. like 2 volts or 30 volts... (the 10 ohm resistors will pop)
So the process is to chassis ground the black dmm lead, turn on the power and read the voltages found on pins 10, 13 and the resistor's common pin 19 with the red dmm lead.
IF any voltage is GREATER than one volt either positive or negative, shut it down
IF the voltages are within 0.4v to 0.99 volt continue:
then while reading the voltage on pin 10, turn the VR1 pot on the side of the board and see if it causes any of the voltages to rise a few millivolts (example: ten millivolts = 0.010V). write down the new pin 10, 13 and 19 voltages. we WANT to see this voltage shift, they should ALL shift (maybe not pin 19) - sort of like the tide lifting all boats.
It MAY be possible to use VR1 to adjust the pin 19 voltage to 0.000v - we couldn't on the last one - it stayed stuck on 0.000v. I want to see if it will adjust on this one. don't turn the pot more than a few millivolts (say 10 , meaning 0.010v) difference on pin 10 or 13, gauging this by the amount of rotation of the pot's adjustment, to see if pin 19 does adjust.
If you can, do try to adjust to 0.000v on pin 19. That should make the pins 10(+0.4) and pin 13(-0.4) voltages mirror images of each other.
OK, now for VR2. It is commonly called idle current adjust. It can get confusing.
Idle current is measured as a VOLTAGE. It is a voltage developed across two of the big white rectangular 0.5 ohm resistors (0.5?k) on the amplifier board BECAUSE of the idle current that is flowing through them.
WHY does the idle current flow?
Because the +0.6v on pin 10 and -0.6v on pin 13 tell the output transistors to turn on SLIGHTLY. ONLY slightly!!
The fly in the ointment is that every transistor is DIFFERENT just a little bit. One might work at 0.602v, another at 0.580v
This circuit starts at about +/- 0.400 volt or so, just to be safe.
Thus we have this VR2 adjustment, to find the "magic point" where the output transistors turn on and start conducting current.
When VR2 is increased from zero, the pin 10 voltage will get larger in the positive direction, and the pin 13 voltage will get larger in the negative direction.
LATER EVENTUALLY
WHEN the output transistors (one NPN transistor that works on +0.6v and one PNP transistor that works on -0.6v)
are in place, the idle current will suddenly turn on as the "magic point" is hit. This will cause a shift in the pin 19 0.000v you set, because there are TWO transistors (+0.602, -0.580 remember?) - so don't be concerned.
We want to trial adjust the VR2 up to see, let's say, +0.7v and -0.7v.
Do not go higher, the 10 ohm resistors will burn up.
THEN turn the VR2 back to the zero ohms position, and try the other amplifier card.
This is a very dense information dump, it will need to be studied. It is both the what to do and why it happens.
