I have a Harman Kardon TC300 which plays low on the right channel. Checked the board for dry joints it looks fine.
Amp doesn't draw excessive current or heat up.
The right and left trim pots do nothing when turned.
Anyone seen this before?
Amp doesn't draw excessive current or heat up.
The right and left trim pots do nothing when turned.
Anyone seen this before?
Does your signal source have grounded shields?
Does the mono/stereo switch make a difference?
Have you confirmed that the voltage in the audio circuit are close to what the diagram shows?
Have you tried tracing the audio through the circuit?
http://www.bcae1.com/temp/harmon kardon - tc300_[ET].pdf
Does the mono/stereo switch make a difference?
Have you confirmed that the voltage in the audio circuit are close to what the diagram shows?
Have you tried tracing the audio through the circuit?
http://www.bcae1.com/temp/harmon kardon - tc300_[ET].pdf
Hi Perry thanks for your reply
Signal source has grounded shields
Mono stereo switch makes no difference
I don't have a diagram to check the voltages
I've completed tracing the audio through the circuit and it all looks ok
Signal source has grounded shields
Mono stereo switch makes no difference
I don't have a diagram to check the voltages
I've completed tracing the audio through the circuit and it all looks ok
So I found some discrepancies around the following transistor in the right channel audio path
Q201 should read -81v on the collector
It measured at - 1.05v
I checked the left channel Q101 and it measured -. 81v
Should I swap Q201 out?
Q201 should read -81v on the collector
It measured at - 1.05v
I checked the left channel Q101 and it measured -. 81v
Should I swap Q201 out?
The difference between -0.81 and -1.05 probably isn't significant but I'm not familiar with this circuit. Q234 could also be making a difference. DOn't change anything yet.
Does swapping the L/R RCAs change the low channel.
What's the resistance between the RCA shield (RCAs plugged in) and the primary ground (no power applied)?
Does swapping the L/R RCAs change the low channel.
What's the resistance between the RCA shield (RCAs plugged in) and the primary ground (no power applied)?
Swapping left and right makes no difference
resistance between rca shield and primary ground is 00.1 ohm
resistance between rca shield and primary ground is 00.1 ohm
Hi Perry when you say gain pots do you mean SW100 and VR100?
I checked SW100 and VR100 and the outer pins marked in RED on the circuit image below had continuity with the negative speaker terminals also marked in red.
I also tested VR103 and VR203 outer pins to speaker negative terminals and there was no continuity.
[/URL][/IMG]
I checked SW100 and VR100 and the outer pins marked in RED on the circuit image below had continuity with the negative speaker terminals also marked in red.
I also tested VR103 and VR203 outer pins to speaker negative terminals and there was no continuity.
SW100 is the mono/stereo switch. The pot closest to the corner of the board is VR101.
VR100 is the gain pot.
VR103/203 are to ensure that both inputs (center conductor and shield) have the same level of drive to the circuit.
Continuity isn't a definitive term.
What was the resistance between the red terminals of VR100 and the negative speaker terminals?
If you place your meter on the red terminal and the other outer terminal of that section of the gain pot, do you see a change in resistance as you turn the pot? 0 ohms to 100k ohms?
Are you sure that you were turning the gain pot when you said it made no difference?
VR100 is the gain pot.
VR103/203 are to ensure that both inputs (center conductor and shield) have the same level of drive to the circuit.
Continuity isn't a definitive term.
What was the resistance between the red terminals of VR100 and the negative speaker terminals?
If you place your meter on the red terminal and the other outer terminal of that section of the gain pot, do you see a change in resistance as you turn the pot? 0 ohms to 100k ohms?
Are you sure that you were turning the gain pot when you said it made no difference?
Last edited:
Sorry for the confusion, I thought vr203 and vr103 were left and right gain pots.
VR100 ranges from
0 ohms to 94.0 on one side and 0 ohms to 93.4 on the other set of red to outer pin
VR100 ranges from
0 ohms to 94.0 on one side and 0 ohms to 93.4 on the other set of red to outer pin
Do you read 0 ohms...
From the gain pot to those 2 caps?
From those 2 caps to the emitters of Q102/202?
From the gain pot to those 2 caps?
From those 2 caps to the emitters of Q102/202?
Last edited:
Q202 Emitter to CP204 negative lead is 0 ohms
Q202 Emitter to CP104 negative lead is 27. 5K ohm
and 65K ohm to the other leg
Q202 Emitter to CP104 negative lead is 27. 5K ohm
and 65K ohm to the other leg