Polytone power supply rehab..can u help? - diyAudio
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Old 9th July 2012, 01:47 AM   #1
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Default Polytone power supply rehab..can u help?

Hi, I am new to the group and love the sound of my Polytone baby Taurus with 8 inch speaker. This thing is old now (like me) so I would think its not too hard to make a "Polyclone' of this thing. I have some electronics background, but never built an amp before...not great at translating the schematic to a PCB. Can anyone recommend a starting point? A book or something to get started with cleaning up this power supply? Its now full of pops and buzzes...probably needs new filter caps...i dont even know which things on the board are the filter caps...or what they do. So..thats where im at. Anybody ?
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Old 9th July 2012, 12:26 PM   #2
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If you post some good pictures of the electronics then maybe someone could point out what needs to be replaced.
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Old 9th July 2012, 09:55 PM   #3
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Default Here are some pics!

GREAT idea! I didnt know you can upload pics here.
This is the amp and the power supply only...I just want to rebuild the power section for now...not sure where to start or where to get supplies..etc...i need some guru mentoring....i would be willing to pay for some one on one tutoring. I have the power transistors out...waiting for replacements.
On this you can see that the large yellow (cap?) is just flappin in the breeze. Well..i have another amp of exact same model..that works perfect, so I opened it up to see where that lead is supposed to connect to. The 'good' amp has the SAME cap just hangin there! but it works!! I do not see where it could have been attached, but there is solder on the end of it..also, it may connect to the nearby resistor...but I cant make that out on the schematic on murch which is blurry..i can post the schmatic if you dont have it...but its here: http://www.murchmusic.com/Polytone%20Info/schem2.JPG but its posted online upside down.
Im hoping that fixes it..but something tells me its not that easy. Please feel free to contact me on this! Chas
Attached Images
File Type: jpg P1000445.jpg (630.5 KB, 58 views)
File Type: jpg P1000447.jpg (737.4 KB, 52 views)
File Type: jpg P1000449.jpg (704.7 KB, 53 views)

Last edited by CHARLIE X; 9th July 2012 at 10:00 PM.
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Old 10th July 2012, 12:00 AM   #4
Minion is offline Minion  Canada
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Well , Changing The transistors will only help if the old transistors are burnt out or you are upgrading the transistors to newer types ...... Transistors generally work or they don"t work with nothing in between , new transistors and old but working transistors will generally sound the same and dont gradually deteriorate with time ......

It looks like that big cap with one end just hanging connects to one of the 2 holes right underneath it , I suspect that trace with the 2 holes in it is where it connects , the other hole probably connects to a wire that probably goes to ground .......
Those types if caps (electrolytics , there looks to be 5 of them) do deteriorate gradually with time which can cause crackling and increased hum , i would suggest you replace those with new ones ........

The ceramic caps (The brown disk looking caps) can be replaced with newer film caps , the ceramic caps that are in there won"t go bad from time but ceramics in the audio path can sound a little brittle ......

The blue caps are probably fine where they are .......

looks like a cool little project ......

PS: the Schematic you posted isn"t the schematic for your amp .....



Cheers

Last edited by Minion; 10th July 2012 at 12:07 AM.
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Old 10th July 2012, 01:03 AM   #5
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wow..thats not the schematic? The layout is very close..but i guess where it says CR1...well..i dont have a CR1.
Any idea where i can find the schematic? Polytone does not exist as far as parts or customer support....I think Murch is the only poly guy around. So, without the sch..how would I know which value new caps to buy? THanks for the response!!
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Old 10th July 2012, 03:07 AM   #6
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Hopefully you did not bend the wire on the end of the cap that is broken off. Itís position, angle etc will give big clues to were it should go.

If your camera has macro ability take a high resolution close up picture of the area you think it came from. Take the pictures from many angles with good lighting. Then crop out everything but about 2 sq inches around were you think it connected. This way you can upload high resolution pics without having large file sizes. If you get the lighting and angle right we should be able to see down those holes and be able to inspect that resistor for any connection.

The pic i uploaded is an example of what can be done with good lighting and a macro camera. This is a automotive relay about 1 inch square in itís case. I wanted to know the condition of the contacts and could not see between the contacts very well. I took about 15 pictures from different angles and one of them caught the light just right.

BTW, this super close up after being cropped is only 167KB
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File Type: jpg asd relay cleaned cropped PIC_0006.JPG (163.1 KB, 44 views)
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Old 10th July 2012, 03:01 PM   #7
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thanks! but..i dont have such macro power on my camera. The lead that is dangeling has not been touched...and it does not correspond to any connection...this is true in both amps.
I went to 'musicparts.com and bought the polytone baby taurus lead schematic...1987...
All the components on the layout match the physical amp...except CR1...no schem shows a cap there...i dont know how to read the CR1 part...is that a rectifier section? Anyway..thanks for the response...still waiting for the new parts..I may be able to replace the caps as noted above. ...soon as i figure out what to order as replacements. THANKS AGAIN ALL!
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Old 10th July 2012, 04:06 PM   #8
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Can you scan schematic and post it.
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Old 10th July 2012, 07:12 PM   #9
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Here is the schm...I believe my amp is the last one...last page.
Thanks for any more help on this...still waiting for transistors and values of the caps to replace. I have not read this deeply yet. Hope this helps someone else out.
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Old 11th July 2012, 12:03 AM   #10
Minion is offline Minion  Canada
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Im 99% sure that the end of that cap goes to the Pad with 2 holes that is right underneath the cap ......
Putting a trace there with nothing connected to it is just not a logical thing for any designer to do and the cap does nothing without both ends hooked up ......
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