Boston Acoustics GTA 800m - Page 3

outoftheblue · 13th November 2011, 04:13 AM

Ok. I installed a 2n6491 (reversed from the original transistor).

I still get the red led for protection mode as soon as I turn on the remote.

Here are the voltages at the 2n6491 pins.

Remote On:
B - 12.05
C - 11.08
E - 12.71

Remote Off:
B - 12.68
C - 0.08
E - 13.06

outoftheblue · 13th November 2011, 06:00 AM

Voltages on TL494 pins:
1 - 2.69v
2 - 0.14v
3 - 0.09v
4 - 0.04v
5 - 1.46v
6 - 3.62v
7 - 0v
8 - 1.47v
9 - 0.36v
10 - 0.36v
11 - 1.46v
12 - 11.03v
13 - 4.95v
14 - 4.95v
15 - 7.21v
16 - 4.95v

Perry Babin · 13th November 2011, 04:10 PM

You need to determine why you don't have 12v on pins 8 and 11. I'm assuming that pins 9 and 10 are used to drive the FETs.

In the future, avoid using hyphens as separators. They can be mistaken for a negative sign.

outoftheblue · 13th November 2011, 10:21 PM

I found that my replacement parts for the 2sa1266 drivers were not pin compatible as I had thought. So I pulled the transistors and fired it up without the two driver transistors. The status Led is now switching back and forth quickly between blue and red.

Here are the DC voltages on the TL494 pins:
pin 1: 2.69v
pin 2: 0.14v
pin 3: 0.15v
pin 4: 0.04v
pin 5: 1.46v
pin 6: 3.64v
pin 7: 0v
pin 8: 5.34v
pin 9: 2.05v
pin 10: 2.05v
pin 11: 5.34v
pin 12: 8.17-12.25v (jumping)
pin 13: 4.95v
pin 14: 4.95v
pin 15: 6.74v
pin 16: 4.95v
(all measurements except for 0v and 4.95v are jumping around)

I am currently powering the amp through a very small battery charger.

Perry Babin · 13th November 2011, 10:46 PM

Without the PNP drivers, the amp is likely drawing excessive current.

outoftheblue · 15th November 2011, 01:46 PM

I replaced the PNP drivers using the correct pin orientation (base and collector were switched) and it works now.

I'm guessing that mistake caused Q1 (the PNP that provides the TL494 with 12v) to fail by drawing too much current.

Thank you very much for your help Perry.

13th November 2011, 04:10 PM	#23
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	You need to determine why you don't have 12v on pins 8 and 11. I'm assuming that pins 9 and 10 are used to drive the FETs. In the future, avoid using hyphens as separators. They can be mistaken for a negative sign. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

13th November 2011, 10:46 PM	#25
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	Without the PNP drivers, the amp is likely drawing excessive current. __________________ 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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13th November 2011, 04:13 AM	#21
outoftheblue diyAudio Member Join Date: Nov 2011	Ok. I installed a 2n6491 (reversed from the original transistor). I still get the red led for protection mode as soon as I turn on the remote. Here are the voltages at the 2n6491 pins. Remote On: B - 12.05 C - 11.08 E - 12.71 Remote Off: B - 12.68 C - 0.08 E - 13.06

13th November 2011, 06:00 AM	#22
outoftheblue diyAudio Member Join Date: Nov 2011	Voltages on TL494 pins: 1 - 2.69v 2 - 0.14v 3 - 0.09v 4 - 0.04v 5 - 1.46v 6 - 3.62v 7 - 0v 8 - 1.47v 9 - 0.36v 10 - 0.36v 11 - 1.46v 12 - 11.03v 13 - 4.95v 14 - 4.95v 15 - 7.21v 16 - 4.95v

13th November 2011, 10:21 PM	#24
outoftheblue diyAudio Member Join Date: Nov 2011	I found that my replacement parts for the 2sa1266 drivers were not pin compatible as I had thought. So I pulled the transistors and fired it up without the two driver transistors. The status Led is now switching back and forth quickly between blue and red. Here are the DC voltages on the TL494 pins: pin 1: 2.69v pin 2: 0.14v pin 3: 0.15v pin 4: 0.04v pin 5: 1.46v pin 6: 3.64v pin 7: 0v pin 8: 5.34v pin 9: 2.05v pin 10: 2.05v pin 11: 5.34v pin 12: 8.17-12.25v (jumping) pin 13: 4.95v pin 14: 4.95v pin 15: 6.74v pin 16: 4.95v (all measurements except for 0v and 4.95v are jumping around) I am currently powering the amp through a very small battery charger.

15th November 2011, 01:46 PM	#26
outoftheblue diyAudio Member Join Date: Nov 2011	I replaced the PNP drivers using the correct pin orientation (base and collector were switched) and it works now. I'm guessing that mistake caused Q1 (the PNP that provides the TL494 with 12v) to fail by drawing too much current. Thank you very much for your help Perry.

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