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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

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Old 5th Feb 2018, 5:49 pm   #1
keith2018
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Default Cambridge P40

Hi all, I have a Cambridge P40 Amplifier (and CD Player & Speakers from the same era). Originally purchased around 30 years ago I doubt if the system has had 50 hours use - long term storage and then the loft - it's a long story, no pun intended.

Having switched it on it was fine for around a 30 minute test. Then went to switch it on the next day and at powering it up it died. I replaced a fuse on the board and it now works, but the left hand channel has no sound - confirmed by swapping speakers around etc. Depressing the Mono button gets sound from both speakers.
For sentimental reasons, and the fact it still sounds so good when it's working, I'd very much appreciate any advice / assistance / suggestions to get it back up and running.

From the image I can see a few marks on the board but I can't see any obvious component damage. From a thread on this board on the same model I did note that replacing the 2 x red Roe is suggested as standard?.

I do have a multimeter and soldering equipment and appreciate electrical safety. An electronics apprentice originally but thats a long time ago now.

I have uploaded a very high quality image at this link:

http://www.keithb.org/P40.JPG

Thank You,

Keith.
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Old 5th Feb 2018, 6:58 pm   #2
Cobaltblue
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Default Re: Cambridge P40

Hi Keith

A few questions

Can you read a circuit diagram?

Can you solder ?

Can you interpret Meter reading or own a meter come to that? ( I see you own a Meter)

If the Answer to all 3 is no then you might consider just buying a working P40 its not rare or particualrly sought after.

If you want to have a go and prepared to master those 3 above or indeed can already answer yes.

First thing to do is to get the circuit diagram and have a look at the standing no signal voltages on both channels.

Cheers

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Last edited by Cobaltblue; 5th Feb 2018 at 7:00 pm. Reason: added Meter
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Old 5th Feb 2018, 7:07 pm   #3
robin coleman
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Default Re: Cambridge P40

They were horrible PCB's to flow solder and the polystyrene caps used to melt. They may need a change
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Old 5th Feb 2018, 7:22 pm   #4
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Default Re: Cambridge P40

Have you cleaned all the switches and pots with contact cleaner?

After that, the first thing to do is to compare the RH and LH preamp supply voltages.

As Mike says, if that is beyond your abilities then you would be best advised to sell it on in a non working state and buy a replacement. Good integrated amps can be bought for less than 50, sometimes a lot less. A forum member may even have something suitable.
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Old 5th Feb 2018, 10:11 pm   #5
sortedradio
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Default Re: Cambridge P40

The good thing is that you have a working channel as a reference. I believe the schematic is available F.O.C. here https://elektrotanya.com/cambridge-a.../download.html

Martin
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Old 6th Feb 2018, 12:30 pm   #6
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Default Re: Cambridge P40

Doesn't sound too bad as both power output stages are working. The schematic in the link is not complete and does not appear to match your amp which uses Integrated Circuits.

Looking at the way the back connector board is wired to the main board, I would start by checking the solder joints and also cleaning the stereo/mono and channel switches.
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Old 6th Feb 2018, 11:44 pm   #7
Ted Kendall
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Default Re: Cambridge P40

I think that circuit is for the original P40, circa 1970.
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Old 7th Feb 2018, 8:14 am   #8
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Default Re: Cambridge P40

Quote:
Originally Posted by PJL View Post
Doesn't sound too bad as both power output stages are working.
That's what I feel too. If they were knackered, then a DIY newbie repair would definitely be out of the question, but in this case, it might be an easyish fix.

Could you post a picture of the failed fuse, please.

N.
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Old 7th Feb 2018, 1:00 pm   #9
keith2018
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Default Re: Cambridge P40

Hi All and Many Thanks for the swift replies.

In answer to Mike's reply: Soldering and using / reading the meter no problem. Reading the circuit diagram is a different issue. I can understand the basics and identify the different components - I'd find it a lot easier if the components were identified by number on the circuit board, which they aren't unfortunately.

Apologies Nick - I binned the fuse, visibly blown and failed a meter check.

I do take the point(s) of getting a replacement Amp. but I'm prepared to spend a little cash on this before I give up on it.

I've decided To replace the 2 x large Cap's T40941 6800 μF and the 2 x red components marked 220/6 v3 EKU anyway as after 30+ years they probably going to be a problem - also, though I didn't see it from a visual inspection but can see it from the hi quality pic there is a worrying couple of marks on the board running between the 2 large Cap's.

I'll also give all the moving parts with a good dose of Servisol as suggested. With that in mind - can anyone suggest the replacements for the 2 x red caps 220/6 v3 EKU which I understand are 3 pin ROE type? I usually get parts from http://cpc.farnell.com if someone could suggest a replacement from there that would very useful.
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Old 7th Feb 2018, 1:50 pm   #10
paulsherwin
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Default Re: Cambridge P40

Bad caps are unlikely to be responsible for the fault. There is a widely held belief in the hifi community that any equipment more than 10 years old needs to have all the electrolytic capacitors changed. They do sometimes fail, but my main amp / tuner / CD player / cassette deck are all over 30 years old and all are on their original caps.

You certainly shouldn't change caps randomly if you have limited expertise, as you are likely to introduce new faults.
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Old 7th Feb 2018, 4:24 pm   #11
keith2018
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Default Re: Cambridge P40

Well, there you go.

PJL: "Looking at the way the back connector board is wired to the main board, I would start by checking the solder joints" - Thats exactly what it was, after resoldering each of the joints it fired up and has been playing through both Speakers with no issues for over an hour.

I had concentrated on the main board for solder faults and had ignored the riser board.

In view of Paul's comment regarding the Cap's replacement I'll leave all as it is and see how it fares over the next few weeks.

Thanks PJL and Very Many Thanks to all for the kind assistance!

Keith.
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Old 7th Feb 2018, 4:51 pm   #12
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Default Re: Cambridge P40

I wouldn't recap in the absence of a fault. If you decide to do it anyway, do them one at a time checking everything still works after each one.
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Old 7th Feb 2018, 5:49 pm   #13
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Default Re: Cambridge P40

Normally I'd agree, but those two brick red ones in the original photo are horrors which either gradually loose value or go short circuit at the drop of a hat. I'd get 'em out ASAP. The rest you can probably leave.
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Old 8th Feb 2018, 10:00 am   #14
PJL
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Default Re: Cambridge P40

Lucky guess and pleased to hear it is working again.
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Old 8th Feb 2018, 3:29 pm   #15
keith2018
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Default Re: Cambridge P40

As studio263 mentions, and I've read a number of similar comments about those particular components they don't appear to have a very good track record. I'm going to replace both and as I'm doing that I'll also replace the 2x 6800mf mentioned above - a very close look underneath those shows a dark ring on the board around part of the circumference of one - I'm confident I can replace them all with no issues.

I'll report back when it's done.
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Old 8th Feb 2018, 7:40 pm   #16
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Default Re: Cambridge P40

Showing my age, the first thing I thought of when 'P40' was mentioned was the slimline 1970 original (I use a T55 tuner daily in my workroom). I believe the later model from the 80's was a goodie though and worth sorting out. the fact that the amp works both channels in 'mono' suggests to me the power amp sections and power supply components are fine (the blowing fuse may not be a problem although a component in the preamp going short momentarily may have caused the blow, but I'm guessing obviously here).

I don't know if anyone feels this is a possible course of action, but trace and check from the input to mono switch. It could be a shorting cap or blown transistor?
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Old 9th Feb 2018, 8:13 am   #17
Craig Sawyers
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Default Re: Cambridge P40

Quote:
Originally Posted by sortedradio View Post
The good thing is that you have a working channel as a reference. I believe the schematic is available F.O.C. here https://elektrotanya.com/cambridge-a.../download.html

Martin
Nope - that is the schematic of the original, late 60's, Design Award winning P40, the innards of which look nothing like the OP's. The original was designed by Gordon Edge and Pete Lee, and Cambridge Audio was set up by Gordon to commercialise the design.

The OP's P40 dates from when Stan Curtis was running Cambridge Audio back in the 1980's. I inherited the remains of the company back in the early 1990's after it had gone bust, I think for the second time, and we (Wharfedale) bought it from the receiver as a going concern. And they were still making product with single sided boards, even at that stage (although in FR4 and not SRBP).

Cambridge Audio is now in the safe hands of Richer Sounds, and I have to say make superb gear under the brand.

Craig
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Old 9th Feb 2018, 11:34 am   #18
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Default Re: Cambridge P40

Yes, Richer era Cambridge Audio stuff is very decent no nonsense hifi and sold at a good price.
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Old 14th Feb 2018, 6:08 pm   #19
keith2018
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Default Re: Cambridge P40

Hi all,

Cap's replaced as detailed. Servisol on anything that moves and I also re-soldered all the switches. It's all good.

It's a vintage system - but it sounds great:

Marantz 65DX CD Player, Tannoy Mercury MK11 Speakers and I've added an old DVD Player to AUX as I can get 700+ MP3 tracks on a single DVD, admittedly at a lower sound quality.

Thanks again for all the kind assistance,

Keith.
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Old 14th Feb 2018, 8:56 pm   #20
Edward Huggins
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Default Re: Cambridge P40

That's a super vintage system - great Tannoys!
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