Denon AVR receiver -- Need Help! - Page 1
Forum section: electronics / repair

author: Bargainhunter
author_rank: Regular Contributor
timestamp: February 23, 2018, 06:44:06 pm
content: I know the answer is staring me in the face but I just can't seem to locate the trouble. I've attached a schematic of the power amp in question. I compared this bad amp against a good amp in the same receiver. If I measure resistance between pins 1 and 5 on connector N102, the good amp is in the megohms but the bad amp reads 4.7 ohms.Any suggestions?Also how do I go about testing smd transistors in-circuit? It's very difficult to hold three leads on these smd transistors with a component analyzer.Thanks in advance,Chuck

author: oldway
author_rank: Super Contributor
timestamp: February 23, 2018, 08:03:27 pm
content: Check resistance between collector and emitter of Q108 and Q109 for short circuit.

author: Bargainhunter
author_rank: Regular Contributor
timestamp: February 23, 2018, 10:43:01 pm
content: That was the problem. Thank you very much.Now a new problem. These transistors were replaced but when I turn on the receiver a few seconds later the relays click on ant the output transistors blow. I checked across the speaker terminals and there is no short. The protection circuit does not kick in but there must be a short that the receiver's protection circuit is overlooking.Any thoughts? Relay shorted? Speaker schematic attached.chuck

author: Quarlo Klobrigney
author_rank: Super Contributor
timestamp: February 24, 2018, 04:31:18 am
content: Since your transistors are DC coupled, when I do it I would always change all of them.A DC bias in the chain from an errant transistor or resistor could blow up the output trannys. A "Shotgun" approach is sometimes needed.

author: Bargainhunter
author_rank: Regular Contributor
timestamp: February 24, 2018, 12:27:03 pm
content: Thank you for your advise.I changed both output transistors in that module.Are you suggesting that I change all 18 output transistors in all 9 modules?Thank you,Chuck

author: Quarlo Klobrigney
author_rank: Super Contributor
timestamp: February 24, 2018, 12:39:33 pm
content: Well for the diagram you posted, how many channels are there i.e. speakers?Q101-112 are DC coupled. Replace them all. They look like TO92 devices. If you leave one defective one in it can go into conduction with the result of POOF!.When you say 9 modules (an odd number) I don't understand. How big is this amp? Where is the output schematic?

author: Bargainhunter
author_rank: Regular Contributor
timestamp: February 24, 2018, 01:05:05 pm
content: Thank you for your interest in my problem.The receiver is a nine channel surround sound home theater unit Denon AVR-X5200W. I attached a schematic of one of the amp modules in my first post. The attachment is named amp.pdf.Each module is connected to the speaker board (speaker.pdf attachment). I replaced Q107 and Q108 as they were shorted (in amp module). When I turned on the receiver, The ready light blinked for a couple of seconds and then the relays clicked on at which time the outputs blew. Normallly the protection circuit should have kicked in and prevented the relays from closing. I do not show a short across the speaker terminals so something is causing the outputs to blow after the relays close. This amp module is for the right front speakers..Chuck

author: Bargainhunter
author_rank: Regular Contributor
timestamp: February 24, 2018, 01:15:39 pm
content: All except the Q108 & Q109 are smd transistors.I can replace them all if necessary. I may be easier to replace them rather to try and test them in-circuit.Thank you,Chuck

author: Armadillo
author_rank: Super Contributor
timestamp: February 24, 2018, 01:43:25 pm
content: Firstly check if VR101 is opened.

author: Armadillo
author_rank: Super Contributor
timestamp: February 24, 2018, 01:56:47 pm
content: Also diode mode check the 3 diodes shown in attached.