Sony XM-2002GTR left channel bias

Dr Zeus · 14th June 2011, 05:53 AM

I got this amp in for repair which the owner said the left channel makes a lot of distortion. Upon tear-down I found the bias is not entirely able to be set correctly; almost as if one of the drivers in this amp is leaking or having some other issue. The distortion is audible through a speaker and visible on the scope. If I set the bias to about 0.004v then about 90% of the distortion goes away, the outputs get a bit warm, and the right channel is still superior. The bad channel has three small transistors which should be the drivers: Q105, Q106, and Q107 leaning against the board's heat sync. Have not yet removed, but while on the PCB all drivers in both channels appear to be measuring the same.

Perry Babin · 14th June 2011, 12:26 PM

Post a photo of the distorted waveform.

Dr Zeus · 17th June 2011, 03:16 AM

Its the top half of the waveform with the abnormality. The scope is set to 2v/div ant 1mS. The input frequency is about 150hz sin wave. The channel that has this distortion gets a bit hotter than the one which is working fine. This is with a test speaker attached. Without the speaker the trace is thin throughout.

Perry Babin · 17th June 2011, 05:31 AM

Did you use exact replacements when you replaced the transistors?

Is the bias set properly?

Dr Zeus · 17th June 2011, 11:16 AM

I actually did not replace anything in this amplifier yet as I could not find any degraded components.

I set and re-set the bias a few times measuring the voltage from center to outer leads of the 0.22ohm two-way resistors. Ive been setting the bias to just below 0.001v at idle. If I set the idle bias to 0.004v at idle the top half of the waveform improves but outputs get pretty hot quick.

Dr Zeus · 22nd June 2011, 03:37 AM

I blew it. Q801 by accidentilly shorting it to the pad right next to it. All I can read o nit is ASY and possibly D1 perpendicular to the ASY. I looked up a bunch of sony schematics and Q801 almost always seems to be a 2sa1162. Is this correct?

Also, I'm still trying to figure out what is wrong with the bias on the left channel of this amp.

Perry Babin · 22nd June 2011, 04:55 AM

KTA1504 in SOT-23

I have the GTW serivce manual. It lists the transistor above for Q801. Email me if you want the manual.

Dr Zeus · 22nd June 2011, 12:40 PM

MMBT2907 (2B) looks similar and slightly superior to KTA1504. I have MMBT2907 in my collection. I'll try it out and see if I can get this amp back to the last state.

I emailed you for the service manual. Thanks!

14th June 2011, 05:53 AM	#1
Dr Zeus diyAudio Member Join Date: Oct 2010	Sony XM-2002GTR left channel bias I got this amp in for repair which the owner said the left channel makes a lot of distortion. Upon tear-down I found the bias is not entirely able to be set correctly; almost as if one of the drivers in this amp is leaking or having some other issue. The distortion is audible through a speaker and visible on the scope. If I set the bias to about 0.004v then about 90% of the distortion goes away, the outputs get a bit warm, and the right channel is still superior. The bad channel has three small transistors which should be the drivers: Q105, Q106, and Q107 leaning against the board's heat sync. Have not yet removed, but while on the PCB all drivers in both channels appear to be measuring the same.

14th June 2011, 12:26 PM	#2
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	Post a photo of the distorted waveform. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

17th June 2011, 05:31 AM	#4
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	Did you use exact replacements when you replaced the transistors? Is the bias set properly? __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

22nd June 2011, 04:55 AM	#7
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	KTA1504 in SOT-23 I have the GTW serivce manual. It lists the transistor above for Q801. Email me if you want the manual. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

17th June 2011, 03:16 AM	#3
Dr Zeus diyAudio Member Join Date: Oct 2010	Its the top half of the waveform with the abnormality. The scope is set to 2v/div ant 1mS. The input frequency is about 150hz sin wave. The channel that has this distortion gets a bit hotter than the one which is working fine. This is with a test speaker attached. Without the speaker the trace is thin throughout.

17th June 2011, 11:16 AM	#5
Dr Zeus diyAudio Member Join Date: Oct 2010	I actually did not replace anything in this amplifier yet as I could not find any degraded components. I set and re-set the bias a few times measuring the voltage from center to outer leads of the 0.22ohm two-way resistors. Ive been setting the bias to just below 0.001v at idle. If I set the idle bias to 0.004v at idle the top half of the waveform improves but outputs get pretty hot quick.

22nd June 2011, 03:37 AM	#6
Dr Zeus diyAudio Member Join Date: Oct 2010	I blew it. Q801 by accidentilly shorting it to the pad right next to it. All I can read o nit is ASY and possibly D1 perpendicular to the ASY. I looked up a bunch of sony schematics and Q801 almost always seems to be a 2sa1162. Is this correct? Also, I'm still trying to figure out what is wrong with the bias on the left channel of this amp.

22nd June 2011, 12:40 PM	#8
Dr Zeus diyAudio Member Join Date: Oct 2010	MMBT2907 (2B) looks similar and slightly superior to KTA1504. I have MMBT2907 in my collection. I'll try it out and see if I can get this amp back to the last state. I emailed you for the service manual. Thanks!

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Sony XM-2165GTX	Dr Zeus	Car Audio	6	6th June 2011 03:40 AM
Sony XM-GTA2022	mike49504	Car Audio	4	12th March 2011 04:05 AM
Sony XM-1004gx	mike49504	Car Audio	33	26th March 2010 08:10 PM
Sony XM-4520	croccodillo	Car Audio	0	14th December 2005 09:19 AM
Sony XM Radio	Sawzall	Digital Source	2	3rd January 2002 04:46 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read