Orion 225r BJT's

ash4kel · 14th April 2011, 04:11 AM

In the process of troubleshooting my 225r, I had found a bad FET and decided I was going to replace them all. Well, in my haste, there are 2 BJT's (one 2n6488 and one 2n6491) on the same side as the FET's. Could someone please let me know where each one is located. I know they are at one end of the amp side by side. Just not sure which one goes in what position. Thanks

Perry Babin · 14th April 2011, 04:48 AM

Are there two orange diodes in front of the transistor locations?

If so, measure the resistance from the striped end of the diodes to the first legs of those two transistors' solder pads. The one that has a direct connection from the striped end to the first leg is the 2N6488.

ash4kel · 15th April 2011, 05:28 AM

I replaced the transistors and the FET's. When I powered up the amp there is a high pitch noise. The vehicle is not on so it is not engine noise. When I turn the gain down the noise also goes down. With the gain turned down, it is hard to hear the noise but when there is no music you can hear it. Also one side would go out. When I turned up the gain a little, that side came back on. It acts as if there is a bad connection because when I touch the gain I can get a crackle with it. What should I look at?

Perry Babin · 15th April 2011, 05:49 AM

Does any combination of switch positions eliminate the noise?

ash4kel · 15th April 2011, 05:23 PM

OK, so I worked all switch positions, gains, crossover switches and crossover points. The only time the noise goes away is when the amp is set for Low frequency. Now as for the noise. The noise sounds like a very fast morse code " clicking ". Again the clicking goes up and gown with the gain. Also the cutting out of the channels has to do with the RCA's. I noticed that when I moved the amp the, the Outer part of the RCA conncetion stopped making contact with the amp housing. At that point the sound would cut out. But when back in contact with the housing the full range of sound would return. Thanks.

Perry Babin · 15th April 2011, 08:20 PM

Disconnect the RCA cables from the amp. What is the resistance from each of the RCA shields to the non-bridging speaker terminals?

ash4kel · 15th April 2011, 09:58 PM

From the shield to the non bridging speaker terminals is in the mega ohms. The meter just keeps climbing the longer they are held on there. But they start in the mega ohms.

Perry Babin · 15th April 2011, 10:05 PM

I think you have an open shield ground. Do you read 0 ohms between all of the shields on the RCA jacks?

ash4kel · 15th April 2011, 10:47 PM

I have .2 ohms between the Input RCA's and .2 between the Aux RCA's, but between any combination of the Aux RCA's and Input RCA's it is open.

Perry Babin · 15th April 2011, 11:36 PM

Measure the resistance between the RCA shield and the RCA shield terminal under the board. You should read 0 ohms as is shown in THIS image.

14th April 2011, 04:11 AM	#1
ash4kel diyAudio Member Join Date: Mar 2011	Orion 225r BJT's In the process of troubleshooting my 225r, I had found a bad FET and decided I was going to replace them all. Well, in my haste, there are 2 BJT's (one 2n6488 and one 2n6491) on the same side as the FET's. Could someone please let me know where each one is located. I know they are at one end of the amp side by side. Just not sure which one goes in what position. Thanks

14th April 2011, 04:48 AM	#2
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	Are there two orange diodes in front of the transistor locations? If so, measure the resistance from the striped end of the diodes to the first legs of those two transistors' solder pads. The one that has a direct connection from the striped end to the first leg is the 2N6488. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

15th April 2011, 05:49 AM	#4
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	Does any combination of switch positions eliminate the noise? __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

15th April 2011, 08:20 PM	#6
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	Disconnect the RCA cables from the amp. What is the resistance from each of the RCA shields to the non-bridging speaker terminals? __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

15th April 2011, 10:05 PM	#8
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	I think you have an open shield ground. Do you read 0 ohms between all of the shields on the RCA jacks? __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links


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15th April 2011, 05:28 AM	#3
ash4kel diyAudio Member Join Date: Mar 2011	I replaced the transistors and the FET's. When I powered up the amp there is a high pitch noise. The vehicle is not on so it is not engine noise. When I turn the gain down the noise also goes down. With the gain turned down, it is hard to hear the noise but when there is no music you can hear it. Also one side would go out. When I turned up the gain a little, that side came back on. It acts as if there is a bad connection because when I touch the gain I can get a crackle with it. What should I look at?

15th April 2011, 05:23 PM	#5
ash4kel diyAudio Member Join Date: Mar 2011	OK, so I worked all switch positions, gains, crossover switches and crossover points. The only time the noise goes away is when the amp is set for Low frequency. Now as for the noise. The noise sounds like a very fast morse code " clicking ". Again the clicking goes up and gown with the gain. Also the cutting out of the channels has to do with the RCA's. I noticed that when I moved the amp the, the Outer part of the RCA conncetion stopped making contact with the amp housing. At that point the sound would cut out. But when back in contact with the housing the full range of sound would return. Thanks.

15th April 2011, 09:58 PM	#7
ash4kel diyAudio Member Join Date: Mar 2011	From the shield to the non bridging speaker terminals is in the mega ohms. The meter just keeps climbing the longer they are held on there. But they start in the mega ohms.

15th April 2011, 10:47 PM	#9
ash4kel diyAudio Member Join Date: Mar 2011	I have .2 ohms between the Input RCA's and .2 between the Aux RCA's, but between any combination of the Aux RCA's and Input RCA's it is open.

15th April 2011, 11:36 PM	#10
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	Measure the resistance between the RCA shield and the RCA shield terminal under the board. You should read 0 ohms as is shown in THIS image. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

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