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View Full Version : Another Crown IC-150 Console on The Bench of Revival


AjaxOfTheRockies
13-02-2021, 04:43
Hi Everyone. I have an IC150 that I am repairing for a friend. Initial problem was popping and noise in the controls, which I fixed with elbow grease and DeOxit.

Now that I can run music through the system and hear it, I discovered the right channel is distorted at low volume and lacking body/bottom at higher volumes. So far, I have confirmed the problem is not with the OpAmp. Then, after reading threads on this forum, I replaced all of the capacitors except for the following:

C2 & C6 .022uf - these are on the High and Low filter pushbuttons on the bottom of the front panel
C129 - 2.2pf
C122 - 2.9pf
C120 - 20pf
C121 - .0015uf - (on order, should be here Monday)
C1 & C8 - 100pf
Anything on the Phono Board - my friend sold all his vinyl.

Also, replaced the 250uf capacitors in the power circuit with 1000uf 50v.

For each capacitor I replaced on the right channel, I replaced the corresponding one on the left for good measure - i.e Replaced C126 and C226 etc.

The problem has not changed and I am wondering if I just need to change out the caps I listed above too, or is there something else I need to check.

Below is a link to a recorded demonstration of the problem. The fade between distorted and 'clean' happens when I pan from right to left and back using the Balance control. No other control changes are made.
The setup is:

Panasonic Tuner > IC150 Console Tuner input > Crown D150 power amp > Bose 901 speakers > Air > My iPhone Voice Memo Recorder

http://www.kkoop.com/IC-150ConsoleProblem.m4a

Can anyone help me track down what is causing this? The left channel sounds really good; If I can get equal quality out of the right, I will be hero for a day

Thanks!!

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struth
13-02-2021, 05:14
Could be the pots.
AjaxOfTheRockies
13-02-2021, 05:26
Could be the pots.

I thought about that, but wouldn't I get additional noise/distortion when rotating them through their range? Nothing I do changes the sound, better or worse. It stays the same.

Would you have suggestion on how to test them? I have multimeter; do I need to pull them out to check readings?

Thanks!

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Puffin
13-02-2021, 07:40
In a vintage amplifier like this it could be a matter of a dry joint or more. Reflowing any that look suspect might help. Here is a link to the service manual. You may need to register to access it.

https://www.hifiengine.com/manual_library/crown/ic-150.shtml
Firebottle
13-02-2021, 09:17
Most unlikely it is going to be any of those small value capacitors causing the fault.
Much more likely is a faulty transistor, good luck.
Barry
17-02-2021, 00:59
This might be of some help: https://www.google.com/search?q=Crown+IC-150+schematic&ie=utf-8&oe=utf-8&client=firefox-b-ab
AjaxOfTheRockies
19-02-2021, 17:19
Thanks for the input, everyone. I appreciate your time to help.

Barry, I have both user and service manual for this unit, so I'm covered there.

Firebottle, I was suspecting that 100pf range caps were probably not involved; thanks for the confirmation. I'm not suspecting a transistor, as the only ones are:


-18v supply regulator
+18v supply regulator
switching for the mute-at-power-on relay
on the Phonograph Input board, which will not be used



Only other semiconductors are some diodes and the two OpAmps


Puffin, I began with an examination of the PC boards and re-flowed solder on the cracked and cold-looking joints. I'm confident the board is solid now. Also, I went through all the controls with DeOxit.

Any other thoughts and suggestions will be very gratefully received.


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Blackdog
19-02-2021, 21:33
How did you verify it isn't an opamp? That's what it sounds like.
Is there any DC at their outputs, both before and after the coupling caps.
You may need a scope to track it down. It would certainly save a lot of time.
AjaxOfTheRockies
23-02-2021, 00:51
How did you verify it isn't an opamp? That's what it sounds like.
Is there any DC at their outputs, both before and after the coupling caps.
You may need a scope to track it down. It would certainly save a lot of time.

I just did a simple component swap to rule out the OpAmp. With left device in the right socket and vice versa, the distortion remained on the right channel.

I haven't measured DC as you describe and will do that now.

I have a scope to follow the signal around, but it looks the same on each side. Could be my scope is too old to help with that kind of detail; or could be I'm too inexperienced with scope to get the best information from it.

thanks for your input!

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