Another Crown IC-150 Console on The Bench of Revival

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13-02-2021, 04:43
AjaxOfTheRockies

Another Crown IC-150 Console on The Bench of Revival

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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13-02-2021, 05:14
struth

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

Quote:

Originally Posted by struth

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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13-02-2021, 07:40
Puffin

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_li...n/ic-150.shtml
13-02-2021, 09:17
Firebottle

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.
17-02-2021, 00:59
Barry

This might be of some help: https://www.google.com/search?q=Crow...t=firefox-b-ab
19-02-2021, 17:19
AjaxOfTheRockies
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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19-02-2021, 21:33
Blackdog

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.
23-02-2021, 00:51
AjaxOfTheRockies

Quote:

Originally Posted by Blackdog

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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