Author Topic: I think I might've killed my astro sonic. :(  (Read 5791 times)

kyuubethe3rd

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I think I might've killed my astro sonic. :(
« on: July 25, 2015, 12:18:48 AM »
Hi folks,

I just finished recapping my astro sonic, there's not an old capacitor in there now!

But, I ran into some issues, I now have a sound issue - the issue being that one side is louder than the other, I didn't have this issue before I put in these last set of caps.

So I reversed the polarity thinking I had these last set of caps wrong and that didn't change anything.

What do you think the issue could be? Are the bottlecap transistors going bad? Or do I have a bad resistor somewhere?

My soldering skills are still a bit elementary, but I really outdid myself with this restoration, I'd really hate to throw this in the dumpster as its a nice unit! :(

eman

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Re: I think I might've killed my astro sonic. :(
« Reply #1 on: July 25, 2015, 11:24:47 AM »
I vote for a cold solder somewhere. Provided you installed the proper values in the right places. Good luck

E
T

spiritofradio

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Re: I think I might've killed my astro sonic. :(
« Reply #2 on: July 25, 2015, 12:03:25 PM »
There really isn't any magic solution, as it could be anywhere in the audio circuit.  However, the nice thing about Stereos, is there is usually 2 of everything.

If you have a multimeter, you can work backwards from the speakers and compare values and narrow down the issue.  Might not be possible if you aren't familiar but if you really want to keep the console, there are resources available that will help get your through the process.






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kyuubethe3rd

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Re: I think I might've killed my astro sonic. :(
« Reply #3 on: July 25, 2015, 04:32:37 PM »
Okay, I redid everything, but I'm still getting the same story. I'm getting readings from all the resistors (I haven't looked into what they should read at though). But when I put it on continuity, I sometimes get multiple beeps; Should I be concerned if I'm getting multiple beeps instead of a constant beep?

Also, I looked at the schematic and I found it odd, the caps I replaced were 250uf, so I got the same ones but with a higher voltage, but however, the photofact calls for 200uf. WTF? Is there some sort of weird factory mod I'm not aware of?

I'm still a newbie, so I don't know where to go from here.

And also, I'm getting a slight buzz, not a powerful buzz (like motorboating) and also a louder hiss than before.

I think I know I dun goof'd when I made things worse. I almost want to give it to someone else and see if they can get it to sound good again.

624Magnificent

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Re: I think I might've killed my astro sonic. :(
« Reply #4 on: July 25, 2015, 08:27:48 PM »
Relax!!

Back up and start at the basics.

Did you replace exactly what you removed? Check each piece. Resistors should be relatively close. Capacitors within 10-20% but with same or higher voltage. Check polarity on the caps...are the arrows / solid lines matching up with the negatives on the surrounding caps?

Check the same component on the other channel... Check polarity, voltage, resistance etc. If there's two channels, speakers etc. there should be twins of each component that match.

Have a beer...relax and go back at it!!
Tom

kyuubethe3rd

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Re: I think I might've killed my astro sonic. :(
« Reply #5 on: July 25, 2015, 10:33:34 PM »
The only thing I didn't replace at exact values was the 5UF caps on the driver board (I used 10UF 50v instead, could this cause issues?), because I couldn't find 5uf caps that could deliver at a reasonable time (I kept finding ones from china), and I also didn't replace a 300UF capacitor with the exact value (I used a 470uf cap instead). I might rework the driver board since I found 5uf caps that seem to be from a reputable brand (vishay).

I'm taking complete shots in the dark here as I have minimal equipment (just a fluke multimeter and a generic no brand capacitor tester).

I've been working on this thing off and on for 3 months and I'd like to end this soon and have it in my room rather than keep it in my basement.

Alan Maier

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Re: I think I might've killed my astro sonic. :(
« Reply #6 on: July 25, 2015, 10:57:46 PM »
Keep in mind that some of those values have changed since the 1960's. The replacement to a 5uf is a 4.7uf, and those are very common. The driver / preamp board is the most common issue with Astro-Sonics, in fact reworking that alone often brings the console back to life and the rest of the caps just peak out the performance.


I recommend jumping across the left and right audio leads between the preamp board and the power amp section. If the audio becomes balanced in mono it's in the preamp board. Jump left / right before and after the volume pot too. You may have a grounding problem there, or a loudness tap issue.


I'd rework the driver board, install 4.7uf caps where the 5uf caps where. You are going to have performance issues.


Also you do want to pull those 470uf caps out and replace with 330uf at some point. Those are speaker coupling caps, and while they likely aren't the problem now, you are asking for problems down the road. Note that Magnavox started the amplifier roll-off above the speaker free-air resonance, the result was the two complementing each other. It's okay if you were working with an Imperial that extends to 30Hz, but otherwise you are going to have a pumped up low bass and an over-driven woofer.


Also remember that for power supply and audio bias circuits, the chassis is positive - not negative.


Also it's very unlikely that you have a transistor issue, especially the TO-3 outputs. Those were so over-rated for their purpose that I've never, ever replaced them.

kyuubethe3rd

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Re: I think I might've killed my astro sonic. :(
« Reply #7 on: July 26, 2015, 12:03:56 AM »
Keep in mind that some of those values have changed since the 1960's. The replacement to a 5uf is a 4.7uf, and those are very common. The driver / preamp board is the most common issue with Astro-Sonics, in fact reworking that alone often brings the console back to life and the rest of the caps just peak out the performance.


I recommend jumping across the left and right audio leads between the preamp board and the power amp section. If the audio becomes balanced in mono it's in the preamp board. Jump left / right before and after the volume pot too. You may have a grounding problem there, or a loudness tap issue.


I'd rework the driver board, install 4.7uf caps where the 5uf caps where. You are going to have performance issues.


Also you do want to pull those 470uf caps out and replace with 330uf at some point. Those are speaker coupling caps, and while they likely aren't the problem now, you are asking for problems down the road. Note that Magnavox started the amplifier roll-off above the speaker free-air resonance, the result was the two complementing each other. It's okay if you were working with an Imperial that extends to 30Hz, but otherwise you are going to have a pumped up low bass and an over-driven woofer.


Also remember that for power supply and audio bias circuits, the chassis is positive - not negative.


Also it's very unlikely that you have a transistor issue, especially the TO-3 outputs. Those were so over-rated for their purpose that I've never, ever replaced them.

So replacing the 5uf spots with 4.7uf's will be totally alright with little to no issue?

I will be ordering some this week! Could it also be possible I put the caps in backwards (I replaced the last 2 50 uf caps recently before my sound issue came up)? (arent they supposed to explode if you put them in wrong...?)

kyuubethe3rd

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Re: I think I might've killed my astro sonic. :(
« Reply #8 on: July 26, 2015, 03:05:37 AM »
I can't find the edit button on this forum, so I'll make a double post. I apologize for the annoyance, moderators.

I believe I might  (EMPHASIS on MIGHT) have solved the problem for now as far as my balance issues. I resoldered one of the caps I recently put in and I left one alone. I was half tempted to put in the old caps to see if that would fix anything (maybe its used to the fact that they're highly rated than marked...?), but I didn't go for it.

The hum isn't as pronouced anymore, only when I flip the plug around is the hum really bad. (this might be because I don't have an isolation transformer)

(OH, there it is)
« Last Edit: July 26, 2015, 03:37:57 AM by kyuubethe3rd »

Pat L

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Re: I think I might've killed my astro sonic. :(
« Reply #9 on: July 26, 2015, 09:03:35 AM »
These units were built before polarized plugs were in standard use, flipping the plug is necessary and normal. It's good to hear you've made progress in resolving the issues.

Alan Maier

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Re: I think I might've killed my astro sonic. :(
« Reply #10 on: July 26, 2015, 09:18:05 AM »
The strong hum when you reverse the AC cord is a giveaway - a capacitor is wired in wrong.  The Astro-Sonics should not be that sensitive to the polarity of the AC plug, so you may also have a failing PS diode. If this chassis has a multi-section can capacitor, keep in mind that it is can-positive.


As for the 50uf, today it's 47uf which is also cheap and common. If you reversed one, they won't explode but will fail, start to bulge and leak. Capacitors do have a safety feature that allows the case to expand and leak before exploding when used with the rated voltage.


Somewhere you have a capacitor reversed. Definitely one that is tied to the common chassis, and most people who deal with more modern electronics (which would still date back to later 1960's) and silicon transistors are used to the common "ground" (using the term loosely) to be negative. Not so with germanium circuits.


You might need to seek out a service manual for that chassis to get these parts installed correctly. With Magnavox, it's not the console model - it's the number on the actual chassis you are working with, and there are little white paper stickers there with the chassis number and date of manufacture... typically a 1Rxxxx type number.

kyuubethe3rd

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Re: I think I might've killed my astro sonic. :(
« Reply #11 on: July 27, 2015, 02:02:25 AM »
The strong hum when you reverse the AC cord is a giveaway - a capacitor is wired in wrong.  The Astro-Sonics should not be that sensitive to the polarity of the AC plug, so you may also have a failing PS diode. If this chassis has a multi-section can capacitor, keep in mind that it is can-positive.


As for the 50uf, today it's 47uf which is also cheap and common. If you reversed one, they won't explode but will fail, start to bulge and leak. Capacitors do have a safety feature that allows the case to expand and leak before exploding when used with the rated voltage.


Somewhere you have a capacitor reversed. Definitely one that is tied to the common chassis, and most people who deal with more modern electronics (which would still date back to later 1960's) and silicon transistors are used to the common "ground" (using the term loosely) to be negative. Not so with germanium circuits.


You might need to seek out a service manual for that chassis to get these parts installed correctly. With Magnavox, it's not the console model - it's the number on the actual chassis you are working with, and there are little white paper stickers there with the chassis number and date of manufacture... typically a 1Rxxxx type number.

>Service Manual

I have a sam's photofact on this chassis. Does that count or is there an official magnavox one that I am not aware of? (my chassis: r20401 40 - made Jan '64)

>50 uf caps

I got some new 50UF caps and they're by sprague (they looked new to me), but they're meant for guitar amps. Do I throw those out for 47uf's?

>Capacitor reversed

Please feel free to look at all the work I've done.

Driver board: https://dl.dropboxusercontent.com/u/62158991/2015-07-27%2001.04.47.jpg
Driver board solder side: https://dl.dropboxusercontent.com/u/62158991/2015-07-27%2001.10.56.jpg

Speaker Couplings (Ignore the 470UF, that will be replaced with a 300-300uf on a user's suggestion but see what I did wrong)
Coupling1: https://dl.dropboxusercontent.com/u/62158991/2015-07-27%2001.05.56.jpg (I might get new caps for these since I might have killed the new caps, but which side is negative since these caps weren't clear - it just had an arrow, so I took a complete shot in the dark)
Coupling2: https://dl.dropboxusercontent.com/u/62158991/2015-07-27%2001.07.37.jpg

I look forward to hearing your feedback, I want to get this thing to sound right and beautiful no matter which side of the outlet I plug in. Also keep in mind, my work is being done in the basement in a house where those grounded plugs are at.

One more thing, I'm on Mouser's site, and does the ripple current matter? Or can I ignore this and just get the 4.7uf 50v and not worry about the rest?

I just hope I can keep my promise to my friend's parents as I promised them I would make this thing sound great again and they wanted to see it work right, too! (Its mine forever, but they wanted to see it work again.)

Thanks for all your help and suggestions in advance. I wish I found this forum sooner (as magnavox friends didn't want to accept my invite) or I would have been done long before yesterday with this amp! :P

Duce67US

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Re: I think I might've killed my astro sonic. :(
« Reply #12 on: July 27, 2015, 09:54:41 AM »
Just looking at the pics, 
On the Driver Board Topside: there are a number of wire terminations (203, 204, 205...)  that are wires wrapped around a post.  It could help to FLUX these and solder each connection.
Done right, it should NOT look like a blob of solder, but you should be able to watch it flow into the joint.
Underneath Driver board:
  Check the + leg of C209 and 210.  The - of 218.   There is a bit of residue from Solder around each of the caps you replaced,  It may help to Clean (Scrub) the joints with 90% Iso. Alcohol and a toothbrush.

In Pic Coupling 1 there is soldier splash on the resister below the LEFT Coupling cap.  So, a melted blob of solder fell into your chassis, and may have also landed elsewhere.   Look for other splashes.   

In Coupling 2 :  On the terminal strip, there is a junction of red wires,  Looks like Loop #6 counting from the left is not Soldered..

While you are in there, grab your ohm meter and check the 470 and 490 ohm resisters hanging off the terminal strip.

Alan Maier

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Re: I think I might've killed my astro sonic. :(
« Reply #13 on: July 27, 2015, 10:14:31 AM »
Great photos! Let me look at those closer this evening and see if something catches my eye.


As for the 50uf you already have - that's fine. Here is the scoop on capacitors... a lot of the values changed since the 1960's, but they are all similar and common. Here are some examples,


2 uf > 2.2uf
5uf > 4,7uf
20uf > 22uf
30uf > 33uf
50uf > 47uf


You get the idea as you multiply the values. The new values are very common and, especially from Mouser, very low cost. Just as long as the voltage rating is the same or higher, you are okay.  No need to worry about the ripple current. I use a lot of "audio grade" caps, but it's simply due to my repairing a lot of tone board and preamp sections of high-end receivers and the cost is just slightly higher. If I bought parts for an Astro-Sonic, I wouldn't spend any extra as it isn't needed. Seems to make a difference on vintage Marantz and Sansui, but it will never be an issue with the "soft" character of an Astro-Sonic chassis.


As for the Sam's - you're okay, but keep in mind that Sam's is often wrong and also Magnavox was known for marking capacitor polarity incorrectly on boards on occasion.


A couple more thoughts for now. Try disconnecting the balance pot from the circuit. Also I am really uneasy over the high level of hum you are getting when you reverse the AC cord. Some is normal, but a lot means there is a problem somewhere. Keep in mind that the console is a stand-alone device. No other electrical connections to the AC mains happens, unlike a component system where you have a turntable, tape deck and CD player each plugged into an AC outlet and also into the receiver. Here the receiver, turntable and speakers are all self contained and common.

kyuubethe3rd

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Re: I think I might've killed my astro sonic. :(
« Reply #14 on: July 27, 2015, 08:45:38 PM »
Thanks for all the tips. I have another amp I got for knobs+parts and its the same chassis model number, too. Can I use how its wired as a reference? The top part speaker couplings have both 200uf caps - I have not touched this one.