Author Topic: Magnavox console / amp repair  (Read 4356 times)

electra225

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Re: Magnavox console / amp repair
« Reply #15 on: July 24, 2016, 03:12:14 PM »
Sal is the capacitor guy.  For coupling caps.  You can buy one or a kit.  You might do a kit, if you are going to get into this heavy.  I like to use 630 volt coupling caps for everything except low voltage applications.  This prevents your having to stock capacitor of several voltages.  Just order whatever value you need at 630 volts for coupling caps.

http://www.tuberadios.com/capacitors/

For the filter caps, I would use Mouser's.  Their website is hard to navigate, but just put "Nichicon PZ" in the search box.  That will save you hassle.  You will want 47uf @at least 450 volts, 500 would be better to replace the 40's.  Use 33uf @ at least 450 volts for the 30's, and then get a 47 uf@ 50 volts for the cathode bypass cap.  If you use Nichicon PZ's you should be able to put the three high voltage caps back in the can, then mount the cathode by-pass cap down in the chassis.  I can talk you thru that if you'd like.  This will make a nice neat installation and you will learn a lot.  I'll be happy to help anyway I can.  The only stupid question is the one you don't ask and it gets you into trouble.  Good luck.

http://www.mouser.com/Electronic-Components/?utm_source=bing&utm_medium=cpc&utm_campaign=Brand%20US&utm_term=mouser.com&utm_content=Brand%20Mouser

I would strongly recommend your going with Nichicon caps in that Magnavox amplifier.  If you were a little more familiar with this stuff, I would have you hot-rod your power supplies like someone was good enough to share with me.  That might confuse the issue.  You can always go back and upgrade after you get a bit more experience.

Have you verified that the power transformer is good?  If it is fried, you are wasting your time doing anything else.  Like washing and waxing you car after the engine blows up.  If the transformer survived this, you might consider fusing at least the primary.  It probably will not save the transformer in the next "short" event, but it might save your house.  Something to think about.  I fuse all my Magnavox instruments when I tune them up.

I found several pictures of how I re-stuff a can cap that might help you.  This is the tuner on my Concert Grand.  First, I mark, then cut the cap can in half.  I take my fist and rip out the old guts.  They come right out with a twist.  Then I bore small holes by the original connections.  You run the wires thru the holes and connect them to the terminals.  Use radial caps for this purpose, I forgot to mention that.  Put the halves of the can back together and seal it with chrome HVAC tape.  You can't tell you've been in there.  I take a felt-tip pen and put the date on the top of the can that I re-stuffed it.

« Last Edit: July 24, 2016, 03:42:46 PM by electra225 »
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PtrkLnk

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Re: Magnavox console / amp repair
« Reply #16 on: July 24, 2016, 07:44:39 PM »
I guess in regards to the power transformer and rectifier let me see if I am understanding things clearly. The power transformer takes the electricity from the wall and transforms it into a different voltage and then the rectifier transforms that from AC to DC?. I see in one of your previous replies you talked about testing the rectifier tube and / or the power transformer however the only diagnostic equipment that I own is a DVOM so my options are a bit limited. Is there a way to test the transformer using with only that or will I need to find someone who has more equipment?

If the transformer and rectifier test okay I am plenty capable of replacing the capacitors and resistors myself, but I am not sure how to get to that point.

AlexanderMartin

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Re: Magnavox console / amp repair
« Reply #17 on: July 24, 2016, 11:23:06 PM »
if you're not comfortable doing this, I live in moline and I'm about 1h from you. Totally down for fixing her up and getting her going. If not keep on listening to Electra, his advice is solid though you could always use the Panasonic ECQ caps for the coupling and not deal with another site, I like ordering all my parts from one source, makes life easier.

AlexanderMartin

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Re: Magnavox console / amp repair
« Reply #18 on: July 24, 2016, 11:25:25 PM »
I feel stupid not reading your last message.
You can use the continuity function to test the windings of your transformer. The windings are usually color coded with say two yellow wires for filaments and two red wires for B+ ect ect. If you have say 10-20 ohms you're good, what you want to watch for is if it's open.
As for the rectifier, connect the positive end of your probe (the red one) to the 'output' of your rectifier 9see the schematic where the voltage goes into the first cap) and one to ground, and set it to DC. If it reads like it should on the schematic, you're good.

electra225

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Re: Magnavox console / amp repair
« Reply #19 on: July 25, 2016, 08:35:01 AM »
I'll be happy to help anyway I can.  This is not rocket science, and if I can do it, anybody can.  I would strongly recommend that the OP learn to read a schematic diagram and learn to perform some basic troubleshooting procedures before attempting to service a Magnavox stereo as his first project.  Learning basic safety procedures will benefit both him and the instrument under test. 

Alexander's offer of help is commendable and might be the best option.  However, if the OP is intending to enter this hobby and do his own work, he is not going to learn much by having someone else fix his stereo for him.  Good luck with whatever you decide.

I recommended that the OP go to Sal for coupling caps because not only the price, but also there are not as many options at Sal's.  Not as much chance for confusion and frustration.  As to Panasonic coupling caps, I see no reason to pay more just to get a fancy name.  I have never had a problem with Sal's caps, and he gives good service.  And he is a little guy and I like to give a little guy a taste when I can.
If it ain't broke, call me.  I can break it....

AlexanderMartin

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Re: Magnavox console / amp repair
« Reply #20 on: July 25, 2016, 12:20:12 PM »
A .01uf 630v cap from sal is .30c a pop. in bulks of ten it's $2.80.
A .01uf 630v from panasonic costs .40c a pop, but in bulks of ten only $1.98. That's fairly substantial and they're excellent quality caps.

So not only you save on the bulk cost of the parts, you save on shipping, and you get a quality name brand part as a result, all on one website. 

http://www.mouser.com/Panasonic/Passive-Components/Capacitors/Film-Capacitors/_/N-9x371?P=1yzvjj0Z1z0wpzo

Scroll down the white ones until you hit the red units.

PtrkLnk

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Re: Magnavox console / amp repair
« Reply #21 on: July 25, 2016, 07:11:25 PM »
The power transformer has five pairs of wires. I tested the continuity of the pairs and found the following:


Green and green with yellow stripe - 0 ohms

brown and brown with yellow stripe (tuner power) - 0 ohms

red and black with a red stripe 2 - 2.8 ohms

yellow and yellow - 0 ohms

red and red - 113 ohms

Any thoughts on what this could mean? Is the 113 ohms too far out of spec?

Edit: I took another look at the schematic that I now have printed out and it looks like they label what each coil should have for resistance. They all are what they should be except it says the red one should have 54 ohms and I am reading it at 113. Is this a problem or is this within tolerance?

AlexanderMartin

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Re: Magnavox console / amp repair
« Reply #22 on: July 25, 2016, 07:48:05 PM »
That could be a factory change. If the voltage is marked on the schematic, measure it and see if it's right. As long as the windings aren't open you're good for the most part.

PtrkLnk

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Re: Magnavox console / amp repair
« Reply #23 on: July 25, 2016, 08:49:04 PM »
Well from what I can tell it is producing the voltage that it's supposed to, and the rectifier seems to be working. Is my next step to replace those capacitors and resistors or is there more diagnostics I should do?

AlexanderMartin

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Re: Magnavox console / amp repair
« Reply #24 on: July 25, 2016, 08:52:46 PM »
If you could actually check the voltage that would help, otherwise check the resistors and change caps at that point.

electra225

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Re: Magnavox console / amp repair
« Reply #25 on: July 25, 2016, 09:16:05 PM »
Pull the rectifier and check the voltages on the power transformer at the rectifier socket.  That is the easiest way to check.  Keep in mind the with no load on the power supply the voltages on the transformer running by itself may be higher than that given in the schematic.  If those are verified as being correct, and there is no smoke or noise, you are safe to go on with the repair work.

I do not intend to belabor this point, nor to get into a pissing contest over caps, but the price quoted for 25 EA of the .01 @ 630 volt axial lead caps at Sal's is $6.25.  That makes them  25 cents apiece, which, at the price you quoted from Mouser's is 10.7% less.  THAT is substantial.

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voxACthirtee

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Re: Magnavox console / amp repair
« Reply #26 on: July 25, 2016, 10:04:23 PM »
the 113ohm spec is close enough because you are measuring red to red.
the reading for 54 would be from the center tap (red/yellow) to one red.
on the sams i have, one "side" is 54 ohms, the other "side" is 50 ohms.
or 104ish

PtrkLnk

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Re: Magnavox console / amp repair
« Reply #27 on: July 26, 2016, 05:58:14 PM »
Well the voltages are what they should be so I think I lucked out and the power transformer is okay. I am going to go ahead and order the capacitors I think.

AlexanderMartin

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Re: Magnavox console / amp repair
« Reply #28 on: July 27, 2016, 06:08:10 PM »
To put it short, the panasonics cost 19c a piece if you order over 10 of them, read my post please. If you ordered 25 of them at 19c they cost 4.95, they cost two bucks less. Let's leave it at that good sir. 

And sounds like you're in a good place. Good luck on the restoration and if you have questions feel free to ask us.

Motorola Minion

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Re: Magnavox console / amp repair
« Reply #29 on: July 29, 2016, 01:23:47 PM »
Pat, I will be following your restoration progress. I just brought home a 1962 Magnavox 1ST659A with the 9304-00 Amp and have not had time to check it out yet. I will be facing the same issues no doubt.

This schematic* posted in downloads http://vintagehifi.net/index.php?action=dldir;sa=details;lid=54is what I will go by rather than the Sams 586 version, since there were some subtle differences.  - *Thanks Pat L!
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