Cambridge Audio Azur 851A dead - Page 1
Forum section: electronics / repair

author: sean5302
author_rank: Newbie
timestamp: September 09, 2020, 03:42:09 pm
content: Please help me guys.I have a Cambridge Audio Azur 851A amp that is dead.I've taken the casings off to see if there's anything obvious. There isn't.I wanted to check fuses, mosfets and capacitors but it's very hard without removing everything first. I see I need a hot air gun because I'm attempting this with a soldering iron.I have no schematics or diagrams and Cambridge Audio (Richer Sounds, really) refuse to supply anything.Any help you can give me will be greatly appreciated, please.All the repair shops seem to be closed down, owners retired etc. Nobody seems to fix things anymore. This was a £1400 amp and I live in Yorkshire. I can deliver it anywhere but I'd like to fix it.I have a Philips oscilloscope, a capacitance meter and a multimeter.

author: SpecialK
author_rank: Regular Contributor
timestamp: September 09, 2020, 04:42:10 pm
content: Those redish brown round things on the vertical board on the right are fuses. They are through hole (I've seen them socketed). Test with your multimeter in continuity mode.

author: Audiorepair
author_rank: Frequent Contributor
timestamp: September 09, 2020, 08:46:41 pm
content: This is why I won't repair hi-fi.

author: SpecialK
author_rank: Regular Contributor
timestamp: September 09, 2020, 10:17:07 pm
content: Quote from: Audiorepair on September 09, 2020, 08:46:41 pmC'mon you can be more helpful than that! I can tell from your post history that you have a wealth of experience.I have very little experience with this type of thing. I think I would start by trying to see if there is standby power. Does a standby LED light up when plugged in and the hard switch on the back is in the on position? I see there is a large toriodal transformer for the audio power, and a smaller toroidal transformer at the back near the power socket and switch.Typically the larger transformer isn't energized during standby to save energy. So the small tranformer is used to create 5V rails for the logic circuits. So locate the standby power board(presumably the board on the right) and check usual suspects like those 85C capacitors and the voltage regulators that are likely under the heatsink just behind the volume encoder.

author: EHT
author_rank: Frequent Contributor
timestamp: September 09, 2020, 10:18:26 pm
content: QuoteNo-schematics is because it's new rather than Hi-Fi, surely? Little chance of manual -see hereMy view is that you don't need the latest model of Hi-Fi amp. Unlike other parts of the chain, the old designs are not obsolete tech. I have an Arcam which is of the ideal age (IMO) where they made proper service manuals and used standard discrete parts. Still, apart from the control board, the parts in this amp may be OK too.I notice this amp has a quirky "class XD" design which is basically Class AB with extra complexity to shift the crossover point away from 0. No idea if that is really an audible improvement but it will certainly make the circuit more complex / harder to debug.Anyway, Sean, if you aren't confident with fault finding and repair this is probably not be the place to start! It seems like the boards are jammed together in a way which will make servicing it hard. Bear in mind the amp will have lethal voltages in it and you have the risk that it might literally go up in smoke from attempts to fix itIf you're comfortable with both risks then hack away! Otherwise did you get a quote from Richer / CA to fix it?

author: SpecialK
author_rank: Regular Contributor
timestamp: September 10, 2020, 01:05:39 am
content: The 840A seems to be very similar in topology from the under-bonnet photos on-line:https://elektrotanya.com/cambridge_azur_840a_sm.pdf/download.html#dl

author: ambrosia heart
author_rank: Regular Contributor
timestamp: September 13, 2020, 04:20:30 am
content: Follow these steps and jot down your results. Never give lengthy description. I won‘t read them in detail.Step 1.Step 2.Step 3.Check 1,2 and 3 first. They are of paramount important to make your amp undead or not be a brick!

author: Spendor
author_rank: Newbie
timestamp: October 11, 2021, 11:16:53 pm
content: Hi there - i have same problem as the one that started this thread. I have a blue power led on front panel but no action at all. I have checked power supplies and have the necessary 5v, 9v and +/- 15v supplies. It just seems that there is no action from the front panel to get the main relays to kick in. Any help much appreciated!