Marantz 2275- Slight imbalance in BA312 output signal strength

sanjib

sanjib

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I have fully restored and recapped 2275. In the preamp all the electrolytic capacitors and transistors HE03-06. Here is what is the problem I am encountering. I am having a little bit of difference in the strength of the output signal from pin 6 of BA312s. The input signal strength at pin 2 is exactly the same.

Here is a numerical example: the signal strength measured at pin 2 of both BA312 42 mV and I am getting a difference of 8 mV from pin 6 of BA312. An ultimately the difference in preamp output is 10 mV and which is becoming almost 240 mV at speaker outputs.

Although tone switches comes after BA312 I have extensively cleaned those switches. I have checked the values of all resistors in the BA312 part of the circuit and they are identical in both channels.
The only difference I am getting is in the voltages at pin 1 and pin 6. The weaker one has 2.139 volts and 11.33 volts at pin 1 and pin6 respectively whether the little louder channel has 2.238 volts and 10.55 volts respectively.

My guess these differences in voltages is not the reason (I may be wrong). I swapped the BA312 but the problem remains on the same channel.

Any help or insight will be great!
 
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Interesting. I'm troubleshooting almost the exact same problem in my recently recapped tone board in another thread on my 2265 which uses the same board. In my case, the right channel is significantly weaker than the left and the tone controls don't seem to work on that weaker channel. Haven't found the answer yet but with some help I'm getting closer. I'm starting to wonder if these BA312's are just wonky and don't respond well to a recap in some cases? IAnyway, I'll let you know what I find out and be watching your thread as well.
 
Sci85 said:
Interesting. I'm troubleshooting almost the exact same problem in my recently recapped tone board in another thread on my 2265 which uses the same board. In my case, the right channel is significantly weaker than the left and the tone controls don't seem to work on that weaker channel. Haven't found the answer yet but with some help I'm getting closer. I'm starting to wonder if these BA312's are just wonky and don't respond well to a recap in some cases? IAnyway, I'll let you know what I find out and be watching your thread as well.
Click to expand...
One short answer: Clean, clean, and clean the switches if you have little imbalance without any considerable distortion! I took out the tone switches from the board and cleaned them four times and it is working fine for now!! This is my fourth 2275 restoration and this is the first time got such dirty switches!
 
Volume tracking, (channel to channel 'balance') is not generally specified for Marantz receivers, but the tightest spec I have seen is 1dBv (volume control setting dependent) in some preamps, others spec it at 2 to 4 dBv .

I suck at math, but by my calculations, your channel to channel difference at the BA312 outputs is only 1.5dB.
Maybe others with better math skills can correct me. 20 Log((42+8)/42) =1.541dB(v)

Tom
 
catrafter said:
Volume tracking, (channel to channel 'balance') is not generally specified for Marantz receivers, but the tightest spec I have seen is 1dBv (volume control setting dependent) in some preamps, others spec it at 2 to 4 dBv .

I suck at math, but by my calculations, your channel to channel difference at the BA312 outputs is only 1.5dB.
Maybe others with better math skills can correct me. 20 Log((42+8)/42) =1.541dB(v)

Tom
Click to expand...
Tom
Yes, the difference is little and after more cleaning of pots, the difference becomes 1mV that is under the error bar of the measuring instrument!
I am not getting more than 10 mV differences at the speaker output and it is impossible to hear the difference.
 
@sanjib - I'm troubleshooting my own issue with low output on the right channel. One thing I am struggling with is getting a proper measurement from the output of the BA312's. Using a 1Khz sine wave input and volume at about 10 o'clock, I see 27.5mV ac on pin 2's but when trying to measure the output at pin 6, my DMM just jumps around and I cannot get a good stable reading on either one of the outputs. When you measured pin 6, were you getting a stable reading and were you measuring at the actual pin? Thanks!
 
sanjib said:
Try to measure at the positive leg of CE13 and 14 (3.3uf) in each channel.
Click to expand...

@sanjib - we tried that as well but got the same unstable reading on the positive legs of CE11/13 as well as CE12/14. However, I did get readings on the negative legs of 155mV and 151mV. It's very odd to me why I can't get a stable reading on the positive side or pin 6. o_O
 
Anyway, you don't have much difference in pin 6 between the two channels and it is passing the signal as you get the measurement at negative legs. What is the difference in AC voltage at pins 7 and 6 of the PE01 connector? If you have a big difference and you have new transistors in place for HE03-06 then you have to take bass, mid, treble knobs out of the board and clean it extensively at 2-3 cycles better with Deoxit D100L rather than D5.
 
sanjib said:
You are having the same problem in the good channel too?
Click to expand...

Yes. I cannot get a stable reading at all on pin 6 of either BA312. Can't understand why...

sanjib said:
Anyway, you don't have much difference in pin 6 between the two channels and it is passing the signal as you get the measurement at negative legs. What is the difference in AC voltage at pins 7 and 6 of the PE01 connector? If you have a big difference and you have new transistors in place for HE03-06 then you have to take bass, mid, treble knobs out of the board and clean it extensively at 2-3 cycles better with Deoxit D100L rather than D5.
Click to expand...

Yes, I had 220mV on pin 6 and only 32.8mV on pin 7 hence the muted output in the right channel. This was with the tone mode switch in the OFF position so the bass/mid/tre were not in the path. I have the same problem however with the tone mode switch off or on but it's a little worse when engaged. I will try some contact cleaner on them instead of just D5.

sanjib said:
Did you replace CE11/13 and CE12/14 with new EC/film caps?
Click to expand...

Yessir. I replaced CE11/12 with 22uF 35v Nichicon UPW caps and CE13/14 with a 3.3uF 50V wima film. Thanks!
 
I think your BA312 parts of the circuit is working fine. You should concentrate on the output part. you should check all of the resistors there and compare with the good channel and if you did not replace transistors yet you should do that. If you swap the BA312 and if nothing change that will definitely eliminate BA312 parts of the circuit from the probable list of problems.
 
Yeah I've replaced all the transistors with parts documented in the thread. I haven't touched any of the resistors though and I was thinking I should start testing those starting with RE55 and 53. What do you think about the readings on HE06?
 
AC signal voltage at connectors pins 6 and 7 should be exactly the same as AC signal voltages at emitters of HE04 and HE06. If you get different then the problem is in the measurement.
 
Yep will do Sanjib thanks. I'll post up on my thread where I'm actually taking the measurements on the board so ya'll can double check I'm not doing something stupid.
 
catrafter said:
Volume tracking, (channel to channel 'balance') is not generally specified for Marantz receivers, but the tightest spec I have seen is 1dBv (volume control setting dependent) in some preamps, others spec it at 2 to 4 dBv .

I suck at math, but by my calculations, your channel to channel difference at the BA312 outputs is only 1.5dB.
Maybe others with better math skills can correct me. 20 Log((42+8)/42) =1.541dB(v)

Tom
Click to expand...
Your math is correct Tom!
 
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