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Post by Deleted on Mar 8, 2015 15:26:32 GMT
 Here's a pic of the extra boards near the speaker outputs. Again,my here are two, so both would have to have the same fault if they were to blame. I've taken a short video of the "trapped Mozzie" noise and will post it. |
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Post by Deleted on Mar 8, 2015 15:29:58 GMT
OK, so the first few seconds after switch on, the whine is really quiet. When the power amp trips in, it gets louder but stays at that level no matter what volume you select or what input you use. When you switch off the whine rises in pitch before the "whoop" sound. Have a listen and hopefully the above description should make sense.  |
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Post by istari_knight on Mar 8, 2015 15:32:07 GMT
Yep no worries, you can discount those... I was just curious as to what they were.
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Post by Deleted on Mar 8, 2015 15:35:14 GMT
So it looks like I should replace the bridge rectifier(s) ? One is marked BYW22 and the other (green) one is blank. Any idea what I can replace them with? Also embarrassingly I have no idea how you know what wires to connect where. Are they marked in some way? The green one looks entirely blank unless there is writing in the back. Edit:looks like I can use one of these for BYW22 but no idea what the other one is. www.donberg.ie/catalogue/semiconductors/semiconductors_b-bc/b600c15000f.htmlThanks for everyone's help so far. It's greatly appreciated |
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Post by istari_knight on Mar 8, 2015 15:47:26 GMT
Each one will have 4 connectors, 2 are AC input and the other two are DC+ & DC- outputs. If there are no markings it will take a little detective work, from each one the two wires that connect to the transformer are the AC [these can go either way 'round it doesn't matter]... The pins wire that connects to a capacitors + terminal is DC+ and the pins wire that connects to a capacitors - terminal is DC- simple as that. Clear as mud ?  I posted a link to suitable replacements on the last page. |
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Post by Deleted on Mar 8, 2015 15:54:04 GMT
Brilliant thanks! so both the BYW22 and the little green one can each be replaced by a substitute like the Maplin one you linked to?
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Post by MartinT on Mar 8, 2015 15:54:39 GMT
I meant that I agree that the issue seems to be with the preamp reg but it would most likely whine according to the volume setting, unless it's connected somehow with the load on the power amp's DC. I'm puzzling over why the whine remains at the same volume.
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Post by istari_knight on Mar 8, 2015 16:55:45 GMT
I meant that I agree that the issue seems to be with the preamp reg but it would most likely whine according to the volume setting, unless it's connected somehow with the load on the power amp's DC. I'm puzzling over why the whine remains at the same volume. Rectifiers can be funny things all it takes is one in the bridge to be below par... It does affect both channels and is independent of the volume control IME. The rectifier replacement is not a sure thing but seems a likely culprit & is cheap enough to try. Singularity, yes both rectifiers can be replaced with those I linked. Whilst you have her open, it could be worthwhile replacing those two axial 'lytic caps on the regulator PCB. |
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Post by Deleted on Mar 8, 2015 17:22:47 GMT
Thanks for all your help. I'm off to Maplins tomorrow to get the bits although it might be next weekend before I do the work. I messed my right hand up in a cycling accident a few days ago, so my dexterity is even more limited than usual. Hopefully by next weekend i will be able to move it sufficiently.Right now I cant even hold a cup and I'm typing left handed  |
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Post by John on Mar 8, 2015 17:51:11 GMT
Get better soon
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Post by Deleted on Mar 8, 2015 18:23:07 GMT
Cheers, John. I've got a great incentive with these amps. Thnaks to all the help here, I reckon I have a better than even chance of getting them back to full health myself |
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Post by Deleted on Mar 10, 2015 17:18:33 GMT
I'm going to try and fit the rectifiers. The ones I'm removing are clearly marked and I'm fine with that part. The new ones only have one terminal marked AC and another marked +
Am I right in thinking that + and - are DIAGONALLY opposite each other and so are The two AC pins?
So it the rectifier was laid out:
1. 2.
3. 4.
Pin 3 is marked + so pin 2 would be - ?
Pin 4 is marked AC so pin 1 would be the other AC?
Doesn't matter which way round I connect pins 1 and 4 to the transformer?
Have I got it right?
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Post by Mr Whippy on Mar 10, 2015 18:06:20 GMT
Yes.
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Post by Deleted on Mar 10, 2015 18:14:36 GMT
Yay! Hope for me yet many thanks to all! |
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Post by Mr Whippy on Mar 10, 2015 18:32:08 GMT
I still wonder about the lead as well. But as James has suggested, replacing the rectifiers is a cheap and logical starting point.
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Post by Deleted on Mar 10, 2015 19:34:45 GMT
Oh, that is interesting. I've replaced the rectifiers but the mosquito is still there, happily humming away.
Now I've made up leads for exposure amps before with worrying results. I used 1mm 3 core mains flex which looked identical to what Exposure seem to use in later amps. The thing is, it blew the first two resistors in the preamp.
The lead was correctly soldered because I got a more adept mate to make another and it did the same again. The lead on this older amp is a different beast, having Two extra signal cores, so maybe I can make one up. I have some 5 pin domino din plugs and some 4 core naim interconnect cable.it looks near identical to the Exposure lead.
Being the novice that I am, I am unsure if this is any use? Can I use the 4 cores for L,R,+ and - whilst using the screen for earth? Or do I need some 5 core cable?
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Post by Mr Whippy on Mar 10, 2015 22:08:03 GMT
Does it have 4 cores and a screen? I'd use anything even just 5 single cores just to see if it makes a difference. Draw the connections 1,2,3,4,5, --------1,2,3,4,5, and join them up identifying their colour. From what you say the two bottom connections (2 + 4) on the poweramp din, yellow + grey will be the power + and - with 3 the earth and 1 and 5 being the left and right signal - I think.
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Post by Deleted on Mar 10, 2015 22:11:54 GMT
I'll give it a go thanks. If the lead doesn't fix Ithe buzz, I'm only really left with the on/off switch, the volume pot, selector switch and transformer. Everything else is dual mono and unlikley to be the cause. Thanks again for your help |
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Post by istari_knight on Mar 10, 2015 22:29:55 GMT
Sorry to hear the noise is still present. It may just be easier to do a continuity test on the cable - If theres no breaks then its OK. Head scratching whats causing it... Impossible to suggest anything more specific as I am completely unfamiliar with the amplifiers & theres no documentation available. If it were mine the next thing I would try would be the replacement of the electrolytic capacitors in the preamp. I serviced an old Mclaren [NZ] amp last year that was full of those Philips/BC/Vishay axial caps, every single one was below 5% of the rated value. Sorry I can't be of more help  |
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Post by Mr Whippy on Mar 10, 2015 22:30:32 GMT
Well, I cannot seeing it be the power switch or transformer. Have you tried moving the wires about inside the power amp?
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