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Conion C100 - no sound?


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#31 stragulus

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Posted 06 October 2014 - 10:01 AM

Kicking this old thread. My box has the *exact* same issue as yours with the working alarm. Pops on switching the stereo lever, but the preamp controls don't do anything at all. And it also has the backgrounde noise plugged in. Mine's a Helix by the way.

 

I am still investigating it, thread is in the restauration section (fixing ebay legend). So far I have concluded that both my amp chips work OK. The function switch works OK (I traced the audio signal). It does indeed seem to be an issue with power to the preamp board, or at least that's my current hunch.

 

The power distribution on this thing is really weird. Usually there's a separate print with the transformer on it to drop voltage, a diode bridge to create DC from AC, and a couple of big caps to smooth out the power. Well, there is such a print, but it's missing the filter caps. The output goes to the pcb with the power and alarm buttons on it. From there, multiple wires go to multiple boards. I *think* the main power line goes to the top amp board, which does have several big caps in a corner. Also, from there, a couple of thick wires lead to the preamp board underneath. I don't know if they're supposed to carry power with them, but I have a hunch they do.

 

I hope to find someone who's willing to do some measurements on their box for me, lacking a service manual. I'll create a new thread by then after some more digging.



#32 blu_fuz

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Posted 06 October 2014 - 10:24 AM

Max sold his. I also sold mine with the same issues.



#33 DSMing91

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Posted 18 January 2017 - 08:20 PM

Kicking this old thread. My box has the *exact* same issue as yours with the working alarm. Pops on switching the stereo lever, but the preamp controls don't do anything at all. And it also has the backgrounde noise plugged in. Mine's a Helix by the way.

 

I am still investigating it, thread is in the restauration section (fixing ebay legend). So far I have concluded that both my amp chips work OK. The function switch works OK (I traced the audio signal). It does indeed seem to be an issue with power to the preamp board, or at least that's my current hunch.

 

The power distribution on this thing is really weird. Usually there's a separate print with the transformer on it to drop voltage, a diode bridge to create DC from AC, and a couple of big caps to smooth out the power. Well, there is such a print, but it's missing the filter caps. The output goes to the pcb with the power and alarm buttons on it. From there, multiple wires go to multiple boards. I *think* the main power line goes to the top amp board, which does have several big caps in a corner. Also, from there, a couple of thick wires lead to the preamp board underneath. I don't know if they're supposed to carry power with them, but I have a hunch they do.

 

I hope to find someone who's willing to do some measurements on their box for me, lacking a service manual. I'll create a new thread by then after some more digging.

 

Howdy. Did you ever get this resolved on yours? 



#34 dirtwolf

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Posted 02 March 2017 - 02:23 PM

Hi there! I had this same problem. On circuit board PCB 2 there is a chip Q204 located around the center of PCB 2. The solder on this chip had become loose. When I adjusted the position of this chip the unit started to work again. I am going to go ahead and re-solder the connection today. I really hope this helps!

 

Here is a picture of the problem chip:

http://imgur.com/XYnZ6k3



#35 caution

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Posted 02 March 2017 - 04:22 PM

D204 is a 2SD325 low frequency power amplifier that is part of the alarm circuit. It seems to act as a switch between regular audio and alarm audio. I think if it fails, it leaves normal audio switched off/silenced. I had to replace the neighboring 11V zener diode, D202, to bring mine back to life.

The transistor was fine.



#36 dirtwolf

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Posted 02 March 2017 - 04:55 PM

Thanks for clarifying Caution! Can you give me any tips on accessing the bottom of PCB 2? It looks like I may have to disassemble the whole boombox. I didn't see anything on the board regarding taking out PCB 2 or PCB 3 circuit boards. I already have all the wires labeled and have tons of pictures. Is there anything else I should consider that is specific to this unit? 



#37 caution

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Posted 02 March 2017 - 05:06 PM

You do need to disassemble a fair amount to expose the bottom of the amp board. You have to disconnect and pull out the frame, and undo all the screws for the controls and pull out both the amp board and I/O board under it, as a pair. It's messy and not recommended unless you really need to.

 

I don't think you need to if you are only going to replace small amp board parts. Just clip the leads on the top of the board and solder new parts to those.



#38 Superduper

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Posted 02 March 2017 - 05:13 PM

He said he thought that the transistor had a bad solder joint. Clipping & installing new device from above won't resolve his problem right?



#39 caution

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Posted 02 March 2017 - 05:20 PM

There are parts right next to it on the same node he can solder to.

 

33215511255_d07ddd92fd_o.jpg



#40 Superduper

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Posted 02 March 2017 - 09:27 PM

Perhaps, but a board diagram would be most helpful to be sure if it's doable. Schematics are frequently deceptive or misleading. I have seen components that are right next to each other on a schematic that was actually physically located all the way across the board. Unless the transistors leads can stretch across the nodes, I personally don't like the clip method, especially if lead extensions will be required. Long leads, especially on the base connections, and especially on high gain signal transistors (high hfe or beta) may act as antenna and introduce and amplify unwanted signals. Perhaps it's just me, but I much prefer to solder them in the proper way, even if significant disassembly is required to do that.

#41 caution

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Posted 02 March 2017 - 10:49 PM

I know what your preference is. No question. I guess we need to find out if dirtwolf went ahead with all the disassembly to reflow it.

 

If not, the wildcard is the emitter pin. On my open unit I see R242 right next to it, which goes to the base and collector. The emitter pin's first connection is an inch away at the positive side of C238, but it's a can, so the lead isn't exposed. Tacking a wire to jumper wire J211 would work, but if there's anything wrong with the emitter pin's solder, the connection to C238 will have to loop through the jumper wire and the original trace from J211 to C238. This may not be an issue since it's such a large value electrolytic.



#42 dirtwolf

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Posted 12 March 2017 - 01:48 PM

Hello again! 

I went ahead and disassembled the boom box and resoldered. I haven't done much work on circuit boards so working from the top seemed beyond my skills.

Working great now!

 

Caution, I saw the pictures of your work on your Conion! Very cool!

 

Thank You for the help!



#43 stragulus

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Posted 18 June 2017 - 09:33 PM

D204 is a 2SD325 low frequency power amplifier that is part of the alarm circuit. It seems to act as a switch between regular audio and alarm audio. I think if it fails, it leaves normal audio switched off/silenced. I had to replace the neighboring 11V zener diode, D202, to bring mine back to life.

The transistor was fine.

This was exactly my issue too with the Helix I quoted here years earlier. I think these may die if you reverse the DC voltage on the external DC pin and give it enough juice.