Orion HCCA 225R - Help Needed

[mattdg1]

As the title says, I have a 225R that needs a little TLC. I have two items that I know for sure needs to be addressing with this amp.

First, one of the gain pots does not have a stopping point, so it needs to be replaced.

Second, one of the channels has audible distortion (squeeling/hissing) while in the stereo mode. If memory serves correctly, when switched to mono, the distortion would stop.

I have a gentleman locally that has an oscilloscope and a backgound in electronics repair who has agreed to help me with it. However, he asked that I try to help ascertain a set of schematics. I've been reading on here for a while so I know if a set can be found, it's probable here.

Any help that can be offered would be very much appreciated.

Thanks in advance!!

Matthew

[Perry Babin]

Sometimes, when a pot is turned beyond the stop, the wiper is damaged. In the older Orion amps, the pot was in the feedback loop of an op-amp. If your amp has the same basic circuit, the open circuit in the pot could cause the amp to oscillate.

If you pull the pot and two pads per channel are directly connected, install a resistor ~1/2 the value of the pot in place of the pot (between the pads that are NOT directly connected).

If you can find a new replacement pot, solder the pot in quickly. If you linger on the terminals of the pot, it will damage it.

If you have to pull the pot out of a donor amp, I'd recommend that you use low temp solder alloy (ChipQuik) to remove it. You'll need an iron with a temperature control. If you try to remove it with standard solder, you're likely to damage it. Use standard solder to reinstall it.

[mattdg1]

Perry,
Thank you very much for your reply!

In this particular amp there are seperate gain controls for the left and right channels. Would this change anything?

In the case of this amp, it is the left channel pot that has been over turned, but I believe it was the right channel that had the noise until the right phase dip switch was placed in the mono/bridged position.

Where could I find a replacement pot for this amp?

[Perry Babin]

If the left pot is defective, it's not likely to have any effect on the right channel.

Check with Orion to see if they can supply the pot. It's difficult to find an exact replacement. Many times, the pots are custom manufactured for a particular piece of equipment.

If the noise is significant, it should be easy to find the source.

The following is a partial schematic for a 600.4. The circuits may be similar enough to be of some use.

http://www.bcae1.com/temp/orionparti...icpreamp01.swf