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Old 4th Feb 2019, 7:47 am   #1
retailer
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Join Date: May 2005
Location: Adelaide, South Australia
Posts: 119
Default Denon AVR 1830

Denon AVR-1830
I do the odd repair for a relative of my son's partner, he dabbles in buying and selling older HiFi gear, he recently bought two PA amps in for repair and a third the Denon AVR 1830 explaining that he had been given the Denon as previous tech could not find the fault, it came with the top removed and all of the screws etc in a plastic bag along with a 7815 and 7915 which the previous tech had determined were faulty, he replaced these but there was a further fault he was unable to diagnose - my initial thought was to toss it in the bin without giving it a look BUT after finishing the PA amps I looked into the Denon chassis and found that it had discrete transistors and none of the STK type modules so common 10yrs or so ago perhaps it was worth saving.

It powered up but was shut down by the microprocessor almost straight away - a bit of internet searching for a service manual found that the microprocessor needs to be reset in the event that a fault triggers shutdown by holding a combination of buttons down at the time power is applied, I thought perhaps the previous tech didn't know so I gave it a go with no luck. A bit of probing with an ohm meter found the 15V negative rail was shorted to earth, to remove the 15V supply regulators the complete amp needs to be taken apart as there is no removable bottom panel - definitely not designed for easy servicing. With the regulators and heatsink removed (they need to desoldered as one) I checked them by hooking each up in turn to a 20v supply they both passed the test.

Fault must be elsewhere I thought, a quick check found two negative rail silicon diodes were short. These were replaced and while doing this I thought how can a fried diode cause a short to earth... but doesn't matter this must be the cause of the fault. With the regulators soldered back in I spent some time reassembling the amp but not fully, just enough to make it mechanically stable so it could be powered up only to find the amp was still shutting down within a few seconds...DARN I thought I had it. Those few seconds gave me a chance to check the 15 supply rails and sure enough the negative rail was 0V. A quick check with a volt meter saw the negative rail was once again short to earth on the input side of the regulator, the two replaced diodes were checked and ok'd so where to from here. The voltage regulators were removed once again (good thing Denon use better quality PCb's no sign of the tracks lifting) but found to be working ok however the input of the 7915 showed a short to the heat sink which is earthed, taking a close look at the voltage regs and heat sink, then I saw the original two failed 15 regs were both full plastic packs so they did not need silicone insulator pads between them and the heat sink, the new 7815 did not matter as it was a full plastic pack and required no insulator, but the 7915 had a metal back which is electrically connected to the centre pin which is also the negative rail input - it had no insulator pad. I suspect the previous tech had some knowledge but not enough to know the regulators needed to be insulated from the heat sink, perhaps he just Googled Denon AVR faults and knew enough to desolder and replace the regulators IC's but was stumped once the remained.
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Old 5th Feb 2019, 12:52 am   #2
unitaudio
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Join Date: Sep 2013
Location: Manchester, UK.
Posts: 771
Default Re: Denon AVR 1830

Better detective work than Magnum!

Regards,
Paul
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