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Post by nuradio on Jan 31, 2023 19:12:10 GMT 12
I recently picked up a majestic branded radiogram. It powers up but is faulty, turntable won't move and loud humming comes from the speakers. A big copper coil on the board seems to heat up and is melting/bubbling the yellow wax coat on it. I have attached a couple of pictures but any information or any details on how to repair is appreciated. Ideally I would love to get it back up to full health so it can be operational. Sorry I'm still learning the parts and names so forgive me if I'm not technical |
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Steve
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Post by Steve on Feb 1, 2023 8:38:24 GMT 12
If you're still learning this might be a case of biting off more than you can chew, but if you're lucky its just capacitors. There is a big round grey one on the left of your first photo - and that is likely the main culprit - but possibly not the only one. If the mains transformer (yellow coated copper coil) is bubbling it might be shot - in which case, depending on the voltages it creates, you may struggle to find a replacement these days - and having a replacement one wound will be prohibitively expensive I suspect (but you never know your luck). If you've got lucky, then it hasn't been left on too long, and the windings might still be intact. So, to start with - what writing is on the big grey capacitor beside the transformer? You'll need to replace that first and see how you get on. You will likely need two or three separate new components to replace the original, and they will have to match or exceed the voltage ratings on the existing one. Simple theory: -------------- 1. The incoming mains voltage goes into the yellow transformer, which steps the 230 volts AC (alternating current - looks like a sine wave when graphed) down to the much smaller voltages needed by the transistors. 2. That new, small, AC voltage is 'rectified' (probably by the two small components [diodes] coming off one of the tags on the big grey capacitor) into DC (direct current, like what comes from a battery - but because it just came from AC it still has bumps). 3. This then goes through the big grey capacitor a couple of times to smooth out the bumps. This capacitor works hard over the years, and over time it starts to break down and 'leak' electricity. The leak only gets worse with time and use. 4. One the leak becomes a flood, you get hum as the electrical bumps get through to the main circuitry. The bumps are (depending on the rectifier) either 50Hz or 100Hz - if you listen to a tone at either of those two frequencies it will probably sound like what you hear when you turn it on.
5. That flood of leaking electricity stresses the transformer badly, and it gets hot. The heat causes the wax that is impregnated into the windings (to stop them moving / vibrating) to melt out. Eventually that heat and any movement will cause the fine wires inside to break.
Hopefully that helps - if you let us know what the writing on the capacitor says, then someone can probably recommend what and how to replace it. Cheers, Steve |
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Post by Peter Walsham on Feb 1, 2023 9:10:59 GMT 12
I'll stick my neck on the chopping block & suggest that one or both pairs of output transistors have shorted. Those AC188/189 transistors weren't exactly all that reliable, especially under overload conditions, and are frequently found to be shorted. I suspect that is causing a huge drain on the B+ supply which is overloading the power transformer. If my theory is correct, new transistors will need to be fitted along with a 'Quiescent current' bias check and/or adjustment.
I have to agree with Steve about the possibility of biting off more than you can chew. As far as the turntable on the record changer not turning. This could be caused by a number of reasons. The motor may have seized, the intermediate drive wheel (idler) might be seized, or worse, the rubber edge could have perished & turned in to a gooey rubbery mess, the turntable itself may be seized on its bearing. The motor may not be receiving power, or may even be faulty.
If you happen to live within reasonable distance to Pukekohe, I would be more than willing to help you out, but I would need to see the chassis and record changer on the bench. Unfortunately, It's next to impossible to diagnose problems by email.
Peter
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Post by nuradio on Feb 2, 2023 14:21:26 GMT 12
Hi mate, awesome info, very detailed and gave me lots to work with. The grey capacitor is an elna brand, ce-w 25v 3300, black - neg.
It's going to be a good project I admit, but something to tinker with, was only 50buks in the end. Any info regarding age or anything like that?
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Steve
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Post by Steve on Feb 2, 2023 14:58:06 GMT 12
Your replacement is probably going to be something like this: www.jaycar.co.nz/4700uf-25vdc-electrolytic-rb-capacitor/p/RE6244It's fairly inexpensive, so you don't have a lot to lose in giving it a try. And I'd cut the positive tag with the two diodes going to it right off the old cap, and tack the new one from that floating cut tag across to the negative tag (ensuring you get the polarity correct). Hopefully that makes sense. If it works, great - it can be tidied up. If, like Peter suggests, the problems are in the output transistors then you've got a complex problem that will need parts which are relatively hard to find, and a setup process which would be documented in the service info if anyone actually has it (I'm fairly certain I don't). Majestic service info for these later sets is not likely to be found in most vintage radio collections... but you never know. Cheers, Steve |
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Steve
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Post by Steve on Feb 2, 2023 15:07:39 GMT 12
Here is a rough diagram showing what I mean. Cut the whole tag off, then wire the new cap across from the, now floating free, tag to the negative tag which can remain attached.
The new cap should have a black stripe or dashed arrow-line down one leg which indicates the negative
Oh, and date-wise I would be thinking in the ballpark of early 70's. I grew up in a house built in the early 70's which had lots of glass and cabinetry similar to the design of your stereogram - and now own my own early 70's house which is strikingly similar as well 
Cheers, Steve
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Post by Steve on Feb 2, 2023 23:21:15 GMT 12
www.vintageradio.co.nz/model/majestic/m-q16I might have found the service sheet for this model - I've just uploaded it along with some old photos I have of it. I suspect its the right one, but I can't be 100% Cheers, Steve
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Post by nuradio on Feb 3, 2023 20:14:04 GMT 12
Hey mate, thanks a ton for all the info. il go through it all and take a good a crack at getting it up and running, i noticed when i flick the turntable to 78 the wheel actually does a small turn, so motor must not be seized. but if can get these electrics replaced i may have it all up and running, all parts are their, everything seems to be ok observational wise apart from the heating, melting and humming. appreciate the time youve taken to respond
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Post by nuradio on Feb 3, 2023 20:19:21 GMT 12
Based on the link www.vintageradio.co.nz/model/majestic/m-q16, that is spot on to the photos of what i have, even the warranty booklet has otahuhu auckland aswell, wicked. mine has no legs unfortunately and the base chipboard needs replacing, but can chuck some rimu on it haha |
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Post by Richard on Feb 5, 2023 8:48:00 GMT 12
I suspect the stereo cartridge is a Crystal type (looking at the schematic) these can deteriorate over time by absorbing moisture. It might pay to check if it can still output a signal, a replacement maybe hard to find, otherwise replace it with a ceramic cartridge and add a preamp.
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Steve
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Post by Steve on Feb 5, 2023 14:09:50 GMT 12
Hey mate, thanks a ton for all the info. il go through it all and take a good a crack at getting it up and running, i noticed when i flick the turntable to 78 the wheel actually does a small turn, so motor must not be seized. but if can get these electrics replaced i may have it all up and running, all parts are their, everything seems to be ok observational wise apart from the heating, melting and humming. appreciate the time youve taken to respond No worries, good luck with the first round of repairs... In my experience the motors are pretty robust - what happens is the old grease in all of the various parts of the mechanism goes like a hard glue. 3-in-1 oil and gently working all the mechanism parts back and forth will often unstick them... I have, on occasion, had to resort to heat from a small chefs blowtorch to get things released. Based on the link www.vintageradio.co.nz/model/majestic/m-q16, that is spot on to the photos of what i have, even the warranty booklet has otahuhu auckland aswell, wicked. mine has no legs unfortunately and the base chipboard needs replacing, but can chuck some rimu on it haha I just found example photos that I had that matched your one... so yep, it looks the same for that reason. I expect the electronics are the same as that schematic because it largely matches what I can see in your photo of your circuit board. I've got some schematics for later DRECO stuff, but they generally don't say what particular sets they were used in so its all a bit like guesswork. If its different, I wouldn't expect its by too much. And the legs should be easy to reproduce or find a set in an old second hand store etc. They do pop up on Trade Me from time to time and shouldn't be too hard to modify to fit your one. FYI: The Majestic brand was made by Dominion Radio and Electrical (DRECO) in Otahuhu, Auckland. The circuit was probably used in La Gloria sets as well, and probably a few others (they made radiograms for other companies, like Wisemans in Auckland etc). Keep us posted with how you get on with that capacitor replacement. Cheers, Steve |
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Post by nuradio on Feb 5, 2023 16:31:44 GMT 12
Hey mate, thanks a ton for all the info. il go through it all and take a good a crack at getting it up and running, i noticed when i flick the turntable to 78 the wheel actually does a small turn, so motor must not be seized. but if can get these electrics replaced i may have it all up and running, all parts are their, everything seems to be ok observational wise apart from the heating, melting and humming. appreciate the time youve taken to respond No worries, good luck with the first round of repairs... In my experience the motors are pretty robust - what happens is the old grease in all of the various parts of the mechanism goes like a hard glue. 3-in-1 oil and gently working all the mechanism parts back and forth will often unstick them... I have, on occasion, had to resort to heat from a small chefs blowtorch to get things released. Based on the link www.vintageradio.co.nz/model/majestic/m-q16, that is spot on to the photos of what i have, even the warranty booklet has otahuhu auckland aswell, wicked. mine has no legs unfortunately and the base chipboard needs replacing, but can chuck some rimu on it haha I just found example photos that I had that matched your one... so yep, it looks the same for that reason. I expect the electronics are the same as that schematic because it largely matches what I can see in your photo of your circuit board. I've got some schematics for later DRECO stuff, but they generally don't say what particular sets they were used in so its all a bit like guesswork. If its different, I wouldn't expect its by too much. And the legs should be easy to reproduce or find a set in an old second hand store etc. They do pop up on Trade Me from time to time and shouldn't be too hard to modify to fit your one. FYI: The Majestic brand was made by Dominion Radio and Electrical (DRECO) in Otahuhu, Auckland. The circuit was probably used in La Gloria sets as well, and probably a few others (they made radiograms for other companies, like Wisemans in Auckland etc). Keep us posted with how you get on with that capacitor replacement. Cheers, Steve Attachments:
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Post by nuradio on Feb 5, 2023 16:34:59 GMT 12
I suspect the stereo cartridge is a Crystal type (looking at the schematic) these can deteriorate over time by absorbing moisture. It might pay to check if it can still output a signal, a replacement maybe hard to find, otherwise replace it with a ceramic cartridge and add a preamp. Thanks mate, will give it a look. Get the electrics worked on and see how the turntable goes, I reckon itl be ok based on it looks pretty good quality, not much wear and tear very little dust/grime. The outside shell if the box thos has been battered. |
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Post by nuradio on Feb 8, 2023 19:49:28 GMT 12
Hi,
so bit of an update, replaced the capacitor with the one you sent in the jaycar link and followed all your directions. it fired up, unfortunately i broke the resistors that were at the top of the capacitor, just old i guess. replaced with 1k, atleast i think they are 1k nd not sure what should be there since i cant read the diagram very well. bulbs came on, turntable spun, no heat. i am still figuring the turntable out, its not as easy as just put on a disc and click start, also the resistance is a bit off so its not spinning as good as it should, i think. as i reinstalled the interface a few old solder connections broke and now i have to repair those. so far it seems to be firing, speakers make a very low hum as more of an indication that there is power rather than the leakage hum you suggested. pretty positive outcome, moving closer than further away atleast.
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Post by Peter Walsham on Feb 8, 2023 20:34:34 GMT 12
Are those resistors (that broke) black in colour, with a white stripe at one end? The only things I see on the top of the capacitor are diodes. What do you mean by 'reinstalled the interface'?
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