Crown D150A Problems

hmontgomery · 28th July 2008, 10:44 PM

As a learning project, I have taken on repairing a Crown D150A (before IOC) Amplifier. Symptoms are Channel 1 is distorted, channel 2 sounds fine. using a Tektronix T922 and Heathkit IG-18 signal generator, 8 Ohm dummy load, I find the top half of the sine wave on channel 1 is missing. Channel 2 looks fine up to the rated output of 80 Watts. + and - 45 Volt supply voltages are at about 42-43 volts and 33VAC supply is attached to the board. I measured the signal coming directly from the op amp and again ch. 2 is a nice sine wave, ch. 1 is missing the top half. I measured the voltages on each pin of the op amp and get the following:

1 8.94v 14 9.78 v
2 9.8 v 13 1.08v
3 6.46v 12 9.04v
4 6.26v 11 6.39v
5 -0.1mV 10 6.38v
6 -5.3mV 9 -0.1mV
7 -9.62v 8 0v

The chip is the UA739PC

Any thoughts?

Thanks.

djk · 29th July 2008, 01:34 AM

http://www.crownaudio.com/pdf/legacy...nual_part2.zip

See pg.14

hmontgomery · 29th July 2008, 11:41 PM

Thanks for your reply. I have thet service manual and have gone down the list. Replaced the mentioned caps, diodes check fine. Not real sure how to verify the transisters in circuit and was hoping the voltages on the IC may point me in a direction without removing the transisters to check.

djk · 30th July 2008, 01:55 AM

The IC is probably bad.

I would just replace the IC, and Q102, and Q202 in the good channel (these transistors frequently fail).

hmontgomery · 30th July 2008, 06:52 AM

Thanks again for your help. That sounds like a plan.

Howard

hmontgomery · 12th August 2008, 11:44 PM

Replaced Q102 and it fixed the problem. Replaced Q202 as well. I bought three of the IC's but ebded up not needing them. Thanks for your help.

28th July 2008, 10:44 PM	#1
hmontgomery diyAudio Member Join Date: Jul 2008	Crown D150A Problems As a learning project, I have taken on repairing a Crown D150A (before IOC) Amplifier. Symptoms are Channel 1 is distorted, channel 2 sounds fine. using a Tektronix T922 and Heathkit IG-18 signal generator, 8 Ohm dummy load, I find the top half of the sine wave on channel 1 is missing. Channel 2 looks fine up to the rated output of 80 Watts. + and - 45 Volt supply voltages are at about 42-43 volts and 33VAC supply is attached to the board. I measured the signal coming directly from the op amp and again ch. 2 is a nice sine wave, ch. 1 is missing the top half. I measured the voltages on each pin of the op amp and get the following: 1 8.94v 14 9.78 v 2 9.8 v 13 1.08v 3 6.46v 12 9.04v 4 6.26v 11 6.39v 5 -0.1mV 10 6.38v 6 -5.3mV 9 -0.1mV 7 -9.62v 8 0v The chip is the UA739PC Any thoughts? Thanks.

29th July 2008, 01:34 AM	#2
djk diyAudio Member Join Date: Feb 2001 Location: USA	http://www.crownaudio.com/pdf/legacy...nual_part2.zip See pg.14 __________________ Candidates for the Darwin Award should not read this author.

30th July 2008, 01:55 AM	#4
djk diyAudio Member Join Date: Feb 2001 Location: USA	The IC is probably bad. I would just replace the IC, and Q102, and Q202 in the good channel (these transistors frequently fail). __________________ Candidates for the Darwin Award should not read this author.

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

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Crown sa 20	Newpaltzwonder	Solid State	5	25th May 2011 10:12 AM
crown xls 602 amp	galush	Solid State	0	6th April 2009 04:41 PM
Crown Com-Tech 210 Power Amplifier Crown Com-Tech 210	tyler477	Solid State	1	31st October 2008 04:24 AM
JBL Crown BPX1100.1 problems	shagone	Car Audio	13	2nd May 2008 10:56 PM
crown d150a	khelben	Solid State	19	5th June 2005 11:56 PM


	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

29th July 2008, 11:41 PM	#3
hmontgomery diyAudio Member Join Date: Jul 2008	Thanks for your reply. I have thet service manual and have gone down the list. Replaced the mentioned caps, diodes check fine. Not real sure how to verify the transisters in circuit and was hoping the voltages on the IC may point me in a direction without removing the transisters to check.

30th July 2008, 06:52 AM	#5
hmontgomery diyAudio Member Join Date: Jul 2008	Thanks again for your help. That sounds like a plan. Howard

12th August 2008, 11:44 PM	#6
hmontgomery diyAudio Member Join Date: Jul 2008	Replaced Q102 and it fixed the problem. Replaced Q202 as well. I bought three of the IC's but ebded up not needing them. Thanks for your help.

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

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