No .. TR481/482?( input differential ) voltages on the same FU'd channel.
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CA-610 II Right Channel Problem
- Thread starter Jerry.G
- Start date
Jerry.G
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Checked resistance FR486 measured 391 ohms and resistance across capacitor C500 was 4.71 Kohms so those I guess or OK.
Took two more sets of voltage readings with no load and amp at idle. 1st set of remeasured values had TR 488 out of spec like my original readings but 2nd set had TR 488 close to spec. Hooked up amp but right channel still plays the same....I guess I need to stick with a load on the amp above fault level to see the fault showing.
The last two set of measurements showed the B lead on TR501 with a positive .629 volts where my original reading were -.596 with spec voltage of -.3.........not sure if my original reading was recorded as a negative but was really a positive value, but left channel at least plays.
Enough for today....
Took two more sets of voltage readings with no load and amp at idle. 1st set of remeasured values had TR 488 out of spec like my original readings but 2nd set had TR 488 close to spec. Hooked up amp but right channel still plays the same....I guess I need to stick with a load on the amp above fault level to see the fault showing.
The last two set of measurements showed the B lead on TR501 with a positive .629 volts where my original reading were -.596 with spec voltage of -.3.........not sure if my original reading was recorded as a negative but was really a positive value, but left channel at least plays.
Enough for today....
Jerry.G
New Member
Decided to take a second set of right & left channel transistor voltages with a record calibration signal input to amp, volume elevated enough to ensure right channel was cutting up and 8 ohm speaker connected to right channel. Resulting readings look vary close to my original readings which I wanted to verify in case I made errors in reading the correct terminals of the transistors.
I put these into an excel table and compared all the transistor voltages to the specification voltages to see where each transistor differed. The attached sheets show the 1st and 2nd set of readings and the other sheet shows the specification table.
Also attached a partial schematic with the 2nd readings and specs shown for some of the right channel amp.
It does appear the issue starts with TR488 common voltage being + 8.37 V instead of -1.2 V.
I don't understand how the transistors connected in the circuit will impact each other to determine which on is causing the errors in the voltages.
I put these into an excel table and compared all the transistor voltages to the specification voltages to see where each transistor differed. The attached sheets show the 1st and 2nd set of readings and the other sheet shows the specification table.
Also attached a partial schematic with the 2nd readings and specs shown for some of the right channel amp.
It does appear the issue starts with TR488 common voltage being + 8.37 V instead of -1.2 V.
I don't understand how the transistors connected in the circuit will impact each other to determine which on is causing the errors in the voltages.
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Yep. You have a part thats failing under load. Diode check will only tell you if its shorted or open . They will all most likely check OK with a multimeter..
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Jerry.G
New Member
Diode test completed on R & L channel transistors using a multi-meter. The B to C reading are with the positive lead on the multimeter connected to the B lead on the transistor and negative lead on the C transistor lead. The readings were taken with B on positive and also with B on negative lead as can be seen in the results. I did this to account for the fact that there are NPN and PNP transistors in the amp but decided to check each transistor both ways, if that makes sense. From my limited reading on transistors, I expected positive readings on only half of the measurements to account for the fact I was reading say an NPN transistor with the wrong polarity. The grey shading on the results sheet differentiate between NPN and PNP transistors. See attached readings.
When taking the readings, some voltages rose slowly until "OL" was displayed some I expected to rise or read "OL" stopped at high voltages (around .9 volts) and I am not sure if these readings should be considered an "OL" result or failure of the transistor when they should be "OL".
Some readings resulted in a voltage reading of 0 volts but as long as both channels showed the same readings, I assume it's OK although I don't understand what a 0 voltage reading means on a diode test of a transistor.
Interesting enough all transistor readings from TR481 to TR495 on the Left channel compare very well with the readings from TR482 through TR498 on the Right channel, including the suspected TR488 form previous testing.
I need to digest these results and likely figure out what next to check to help isolate the problem with the Right channel, but some of the reading on transistor in the Left channel look suspect too although the Left channel plays OK.
When taking the readings, some voltages rose slowly until "OL" was displayed some I expected to rise or read "OL" stopped at high voltages (around .9 volts) and I am not sure if these readings should be considered an "OL" result or failure of the transistor when they should be "OL".
Some readings resulted in a voltage reading of 0 volts but as long as both channels showed the same readings, I assume it's OK although I don't understand what a 0 voltage reading means on a diode test of a transistor.
Interesting enough all transistor readings from TR481 to TR495 on the Left channel compare very well with the readings from TR482 through TR498 on the Right channel, including the suspected TR488 form previous testing.
I need to digest these results and likely figure out what next to check to help isolate the problem with the Right channel, but some of the reading on transistor in the Left channel look suspect too although the Left channel plays OK.
Jerry.G
New Member
OK, I have a small 8 ohm speaker that I used to attach to each channel to atleast check the voltages for idle current adjustment. Per manual voltage should be 10 mA + or - 3 mA. Left channel (TP 1 to TP 2) measured 15.0 mV to 15.4 mV after letting it settle out for a couple of minutes. Right channel (TP3 to TP4) measured -6.5 mV to -7.5mV after settling out. I did have the positive lead attached to TP1 and TP3 for these measurements per the service manual. Looks like they both need adjustment, especially the right channel which is negative instead of positive, but adjusting the resistor for that channel cannot change the negative to a positive value, right? Therefore should it be adjusted to a -10mV and can I make the adjustments using the speaker attached instead of finding a 8 ohm resistor?
Don't worry about + or - just adjust to absolute value. If the minus sign bugs you, swap the test leads. Theres no such thing as negative milliamps.
Jerry.G
New Member
Adjusted left channel with VR481 to 9.5mV then left channel VR482 to about 7mV......turning VR482 max to min has at vest only 1mV change with min setting providing highest value of about 7mV. I check VR482 resistance max setting of 1.616Kohms and min setting of 0.2 ohms. Right channel VR481 setting movement had large movement in right channel mV. This doesn't seem right for VR482 to be so ineffective.
VR481 resistance setting for what ever that matters is at 1.300k ohms.
VR481 resistance setting for what ever that matters is at 1.300k ohms.
Jerry.G
New Member
Hooked the amp up to speakers and tuner to give it a try anyway after adjusting the idling current........Max volume can barely hear any sound from right or left channel. Neither move the output meters either ----but saw the phone input was selected by error... Correcting that, the channel performance is unchanged....left plays OK and right still bad.
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Kinda figured it wouldn't adjust.
Are the heatsinks getting very warm. Adjust the left channel back up to around 10-11 mv. --- Did you short any pins when attaching your test probes ?
Jerry.G
New Member
I didn't notice any heatsinks getting very warm, but was not looking for them......Turned amp off to make insulated alligator clips to the test pins, so no risk of shorts.
Left channel is ok and right channel like it use to be since I found I had the input selector on phono by mistake causing no volume at all.
I hate it when that happens.
Jerry.G
New Member
For what it's worth, I updated and corrected the schematic with actual voltage readings and service manual schematic voltage specifications (note these vary somewhat from two schematics I have). This helps me try to visualize things. I posted this before but not showing the entire right channel components and I think it had a couple errors in it too.
Jerry.G
New Member
Black test probe connected to the metal chassis.
