Hi all,
I have a Technics 9020 with a "stuck" left meter. The right channel meter works perfectly.
I am a novice on electronics of any kind, and beyond having a multimeter and a chopstick for poking at stuff, have no diagnostic abilities.
As soon as the protection relay clicks on, the left meter will jump to the -20dB hash and stay there, descending very slowly to the 0 rest after ~15 - 20 minutes.
If it is fed any signal, it will not descend to 0, but rather to the max level of whatever it's being fed.
If I turn it off, even for an instant, it exhibits the same symptoms as before.
STEPS 1 - 5
I've checked the operation points per the below and all are now within spec after warmup (some were slightly off initially).
STEPS 6-9
Using a laptop, a YouTube 1Khz test tone, and the R meter as a guide, I tried to calibrate the L meter per the below, and noted that VR201, 203, and 205, and 211 will not adjust the L meter's behavior. Note that adjusting logarithmic amplifier using VR201 in Step 2 works fine, but does nothing to adjust the -50dB level alignment in Step 7.
Any advice welcome. Thank you very much!
I have a Technics 9020 with a "stuck" left meter. The right channel meter works perfectly.
I am a novice on electronics of any kind, and beyond having a multimeter and a chopstick for poking at stuff, have no diagnostic abilities.
As soon as the protection relay clicks on, the left meter will jump to the -20dB hash and stay there, descending very slowly to the 0 rest after ~15 - 20 minutes.
If it is fed any signal, it will not descend to 0, but rather to the max level of whatever it's being fed.
If I turn it off, even for an instant, it exhibits the same symptoms as before.
STEPS 1 - 5
I've checked the operation points per the below and all are now within spec after warmup (some were slightly off initially).
STEPS 6-9
Using a laptop, a YouTube 1Khz test tone, and the R meter as a guide, I tried to calibrate the L meter per the below, and noted that VR201, 203, and 205, and 211 will not adjust the L meter's behavior. Note that adjusting logarithmic amplifier using VR201 in Step 2 works fine, but does nothing to adjust the -50dB level alignment in Step 7.
Any advice welcome. Thank you very much!
Here's the schematic.
Have you tried reversing the input channels, to determine whether the problem is in the unit or not?
Have you tried reversing the input channels, to determine whether the problem is in the unit or not?
Thanks for the schematic! And yep, issue is definitely inside the unit, changing the inputs makes no difference.
The relay contacts are just before the meter, so the problem could be anywhere in the circuit.
Strange time constant though.
Strange time constant though.
Yeah, the HOLD function is supposed to max out at ~25 minutes which I don't think is a coincidence. So I assume the fault is somewhere in the PEAK HOLD circuit, or somewhere around it?
When performing Step 3(1), the L meter returns to zero upon the test point getting shorted to the chassis. Maybe the relay in the HOLD circuit has failed.
If the R meter works okay, compare the voltages at 409 and 410. They should be the same.
With the above in mind, make sure the mode select switch (peak hold/peak/average) S5-4 (S5-5) and S5-3 (S5-2 and S5-1) work okay - that they are not dirty. Flick it a few times and see if there's any change.
Also, confirm that both set of contacts (relay 2) work; that they close and open together.
The bottom line is... you have a good working channel which you can use to test the faulty one.
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@Extreme_Boky - you, sir, are a life saver!
I measured at 410 and got 0.7v. I measured at 409 and got 0.0v, then both meters jumped, and the unit is now working perfectly, with 409 and 410 both reading the same.
Not sure quite what to make of that, other than the relay in the HOLD circuit must have been stuck?
Either way, it's all calibrated, working great, and hope it stays that way.
THANK YOU.
I measured at 410 and got 0.7v. I measured at 409 and got 0.0v, then both meters jumped, and the unit is now working perfectly, with 409 and 410 both reading the same.
Not sure quite what to make of that, other than the relay in the HOLD circuit must have been stuck?
Either way, it's all calibrated, working great, and hope it stays that way.
THANK YOU.
Could be the JFETs used as a switch... they're capacitors in disguise... and like to hold the charge (as you said: "the HOLD circuit must have been stuck?").
You may have discharged them... like, you may have given them a reset.
You may have discharged them... like, you may have given them a reset.
Sounds electronic possible bad cap on the one channel. Is there sound on both channels? The meter may be showing a actual problem.
Meter's been working just fine ever since measuring 409 and 410. If there are other problems, they're not bothering me at the moment!
And for what it's worth, all the electrolytics pass the eye test - no bulging, no leaking, no discoloration.
And for what it's worth, all the electrolytics pass the eye test - no bulging, no leaking, no discoloration.