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Post by Deleted on Mar 10, 2015 23:25:13 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  Thanks, James I Really appreciate your help. At least the things I'm replacing are adding longevity and I'm gaining experience. I really enjoyed exploring the wiring config and fitting the two bridge rectifiers. I'll do the electrolytic caps in the preamp as you suggest because they are so easy to do on those large pull-out cards. The Exposures really are tailor made for a novice to work on. Loads of space, big components and not too complicated. I'll take your advice on the lead too. My mate has a couple of multimeters so I will ask him to test it. I'm not sure if this is relevant, but I ran the amp for a couple of hours tonight. After a few mins it does get a bit quieter. Also when I switched off after listening for the longer session, it made lesson the whooping noise and died down quicker. I'm sure I will get there and I'm enjoying finding out more about Exposure from a more hands-on perspective! |
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Post by Deleted on Mar 10, 2015 23:30:26 GMT
Well, I cannot seeing it be the power switch or transformer. Have you tried moving the wires about inside the power amp? I haven't tried that but I will give it a go. The wiring is a bit messy in places so there could be something amiss that I'm not seeing. i once had a Nait that made funny noises. Turned out it had a faulty on/off switch which my dealer replaced. God only knows where I'd get a correct looking power switch though. If you think it's unlikely to be an issue, I won't bother until it's the only thing left to try. |
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Post by MartinT on Mar 11, 2015 6:37:04 GMT
Earth continuity?
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Post by Deleted on Mar 11, 2015 7:30:46 GMT
Thanks, Martin. It's prety messy in one particular place where lots of green wires meet from a variety of directions. I will re-solder those joints. Is there anything I could do to test earth continuity?
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Post by MartinT on Mar 11, 2015 8:11:55 GMT
Test chassis to chassis continuity and signal earth to signal earth (they're not necessarily the same thing).
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Post by Mr Whippy on Mar 11, 2015 8:13:14 GMT
Well, I cannot seeing it be the power switch or transformer. Have you tried moving the wires about inside the power amp? I haven't tried that but I will give it a go. The wiring is a bit messy in places so there could be something amiss that I'm not seeing. i once had a Nait that made funny noises. Turned out it had a faulty on/off switch which my dealer replaced. God only knows where I'd get a correct looking power switch though. If you think it's unlikely to be an issue, I won't bother until it's the only thing left to try. Haven't heard of that. You could short the switch to rule it out. Just make sure you short the switch and not the L and N. |
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Post by MartinT on Mar 11, 2015 8:21:45 GMT
Just make sure you short the switch and not the L and N. Could be an underpants moment!!! |
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Post by Deleted on Mar 11, 2015 14:50:42 GMT
Hehe anything's possible with my knowledge and skills (or lack thereof). Good idea though. I once did this with a telly that had a faulty on/off switch and I'm still here to tell the tale. Blew the telly across the room though..............only kidding!
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Post by Deleted on Mar 11, 2015 15:27:00 GMT
I dunno if this is significant but...... The preamp regulator card seems to have an effect. If I move it around, the pitch of the Mozzie sound varies. It's a bit like a tiny moped changing gear. James said to try changing the small caps on the board, which I will do, but does this shed any light on the fault for anyone with more knowledge? The card is pictured early on in the thread.
Edit: on further playng round, I think it's just because I'm messing about with the connection. I will try replacing the caps, checking the earth (although I will need help from a mate for this bit) and also bypassing the on/off.
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Post by Mr Whippy on Mar 12, 2015 8:16:57 GMT
Moving the board will be varying contact resistance between the socket and board and effecting the circuit.
A regulator might also be suspect. You could replace them along with the capacitors. They have sockets, so an easy job.
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Post by istari_knight on Mar 12, 2015 19:28:29 GMT
Can you tell us the code printed on top of the regulators ? [may have to remove one of the stickers to see the entire thing]. Mr Whippy is correct, if one of the regulators is shot it would effect both channels - Its not one reg per channel but one for DC+ & one for DC-.
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Post by Deleted on Mar 12, 2015 21:39:57 GMT
Thanks guys. I've removed the sticker and it's a Raytheon RC4194DB with 14 pins. Now I can find replacements on EBay but the second part of the code is different. Mine says RAYT7816 and the Ebay one says RAYC4284. Are these numbers significant or is the EBay one a suitable replacement. If so I will buy two anyway.
Do I need a special tool to remove and refit the regulators or do I just gently prise the old ones out and push the new ones in?
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Post by MartinT on Mar 12, 2015 22:37:48 GMT
I suspect the 7816 is a +16V regulator, but no idea what a 4284 is. Doubt it's the same thing.
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Post by Deleted on Mar 12, 2015 22:54:26 GMT
I've spent a while looking at data sheets and also quite a few examples for sale. Nobody seems to refer to the later code and some examples have no code on them at all. The data sheets don't seem to show any variants, so I'm assuming all RC4194DB do the same job?
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Post by istari_knight on Mar 13, 2015 7:25:16 GMT
I've not got access to a computer at the minute but if you hold fire for now I'll have a look once I'm online (looking at. Data sheets is a PITA on a 5" screen!)
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Post by Deleted on Mar 13, 2015 7:31:42 GMT
Cheers James. It's a PItA on any screen for me because 99% of it I don't understand  |
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Post by istari_knight on Mar 13, 2015 10:58:38 GMT
Cheers James. It's a PItA on any screen for me because 99% of it I don't understand No worries Okay, looking at the data sheet we can see that RC4194DB are "dual polarity tracking regulators", they have an input voltage of 35VDC>45VDC & the output voltage is set by an external resistor and can be anything between 500mVDC > 42VDC... They are very clever little devices which completely negate the need for a separate transformer winding to supply the preamp, you can simply link them to the power amplifier power supply [that said, we know Exposure didn't do this as there are 2 bridge rectifiers so the preamplifier does in fact have its own secondary winding on the transformer.] The last two characters in the part number dictate which version of the regulator it is [output load current & heat dissipation] DB is the baby of the range offering 100ma current vs 150ma of the DC part. You can replace DB with DC but not vice/versa. Its my opinion that the code beneath the part number printed on the IC's themselves is in fact the manufacture date code [year 78 week 16 on the originals] All said and done, the eBay one's look fine to me. |
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Post by Deleted on Mar 13, 2015 14:09:04 GMT
Brilliant, Thanks James and very kind of you indeed. You explain things very well too. I actually understood all of your explanation. I have now ordered two of them. I already have the electrolytic caps on the way. I will fit both and re-try. I'm really hopeful of a solution, but whatever happens, I am renewing components and building in future reliability as well as learning as I go thanks to contributions here. Very much appreciated on my part. It's actually been more fun than any fully-functioning exposure amp I've bought |
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Post by istari_knight on Mar 13, 2015 16:00:03 GMT
Let us know how it goes  |
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Post by Deleted on Mar 13, 2015 21:15:01 GMT
Something a bit strange has happened. Plugged the Exposures in again today and no Mozzie, tried them again a few hours later and still no Mozzie. What has changed to drive the Mozzie away? Nothing that seems likely to cause a change. 1. I'm using a different mains lead. 2. It's plugged into a different socket on the mains block 3. I removed the regulator board and cleaned the sticker off one regulator I order to read the number. I'd had the regulator board in and out before so it's unlikely to have been a bad contact. It made the same Mozzie sound before its last owner sold it, so I have no clue why it's suddenly decided to behave itself but long may it continue, I still have the bits in their way but will hold off fitting as long as it keeps on singing |
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