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Old 17th Nov 2018, 5:10 pm   #1
michalism
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Default Sanyo G-2601KCA - one channel audio

Hello

I am trying to restore a Sanyo G-2601KCA music centre. I have read some posts related to this system in this forum, but in general, it does not seem to be a popular system

My problem is that only the right channel is working. Left channel is almost dead.
I do not have service manual, so I'm working in blind mode, and being a newbie, this is a real challenge!

Anyhow, I think that the output stage is working, because none of the output transistors seems shorted and if I apply a signal to the base of the transistors I hear a buzz of equal power on both channels.

I checked where the audio signal is fed to the amplifier board, and the input signal on the left channel is too weak! I tried two sources - radio and tape.
that is why I am suspecting a problem with the small board holding the volume and balance controls at the front.

there are two things I would like to ask:
1. how can I completely eliminate the possibility of a bad power transistor? the unit is using germanium transistors, and I do not want to buy replacement parts unless it's absolutely necessary.
2. Can these old green polyester caps go bad? is it possible that they might be my problem.

I forgot to mention that I already replaced some leaky electrolytic capacitors.

Any advice would be much appreciated!!!

Thank you very much in advance!
Michalis
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Old 17th Nov 2018, 5:25 pm   #2
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Default Re: Sanyo G-2601KCA - one channel audio

Have you checked the volume and balance controls themselves? If you hear any crackle when you move them that can be a sign of dirt inside them. That can cause the channel to cut out, especially the balance control. Spraying them with Servisol can sometimes cure the problem, depending if the track inside is not to worn.
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Old 17th Nov 2018, 7:00 pm   #3
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Default Re: Sanyo G-2601KCA - one channel audio

Let us know what test gear you have: DVM?

Then we can advise. It's not likely to be the output trannies.


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Old 17th Nov 2018, 7:14 pm   #4
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Default Re: Sanyo G-2601KCA - one channel audio

Quote:
Originally Posted by Grubhead View Post
Have you checked the volume and balance controls themselves? If you hear any crackle when you move them that can be a sign of dirt inside them. That can cause the channel to cut out, especially the balance control. Spraying them with Servisol can sometimes cure the problem, depending if the track inside is not to worn.
Yes, I have checked the potentiometers. Actually they were very dirty, but I was able to clean them up and the sound now is very clear!
What are the chances that the balance pot is completely worn out only on one side? slim I suppose ?

Quote:
Originally Posted by John_BS View Post
Let us know what test gear you have: DVM?
I have a couple of DMMs, and an (extremely cheap) analogue one. I also have an analog scope and a chinese DDS.

Thank you both for taking the time to answer
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Old 18th Nov 2018, 1:30 am   #5
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Default Re: Sanyo G-2601KCA - one channel audio

What I tend to do with stereo amps with one side playing up is to prod the two channels with an insulated tool. While the unit is on. It will produce a buzz on each channel. The right channel being the same as the left using the same parts as the right, which you know works. If you prod in the same places on the right first then left, you know what should produce a noise and what shouldn't. Often the noise will change and give the game away.
With this method I have tracked down many of fault without resorting to test equipment till I suspect something is playing up.

PS don't short anything out!
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Old 18th Nov 2018, 8:03 am   #6
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Default Re: Sanyo G-2601KCA - one channel audio

If I get your point, the tool you're using can be anything, as long as it is not metal.
As I understand this, the procedure will help with poor connections, cold joints, etc. but how is it going to help with anything else?
I am not questioning your method, I am just trying to make sure I understand it correctly

Otherwise, I think I am failing to understand what is the difference of this method as opposed to feeding a low level signal in various stages of the amp?

PS. Will try not to!
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Old 18th Nov 2018, 4:52 pm   #7
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Default Re: Sanyo G-2601KCA - one channel audio

ok, I may be getting a little closer to a faulty part.

The amplifier part has 4 transistors, let's name them Q1-Q4, Q1 being the closest to the input signal.
I rechecked the input stage of the amp, and at least for the radio signal, both channels were at the same level. But the transistor on the right channel seemed dead. After poking around like Grubhead suggested, I noticed that touching Q3 produced a buzz on the right channel!
Before that, I measured some voltage (I think 1-2V) on the base of left channel's Q1, but there was no voltage on the base of right channel's Q1.

All passives on the amp board are ok, also all transistors give the correct readings on my DMM.
Is it still possible that the transistor is at fault?

In this post, I see that the transistors are 2SC537-D.
What would be a suitable replacement?
Should I change all transistors in one go, or go slow?
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Old 19th Nov 2018, 1:14 am   #8
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Default Re: Sanyo G-2601KCA - one channel audio

Quote:
Originally Posted by michalism View Post
If I get your point, the tool you're using can be anything, as long as it is not metal.
As I understand this, the procedure will help with poor connections, cold joints, etc. but how is it going to help with anything else?
I am not questioning your method, I am just trying to make sure I understand it correctly
I meant a "metal" tool with insulation to protect you from electric shock!
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Old 19th Nov 2018, 7:51 am   #9
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Default Re: Sanyo G-2601KCA - one channel audio

well... I started too cautiously, by using a wooden stick, but then when I found that transistor I used my finger to touch the plastic cap of the transistor, especially since I knew the voltages around it.
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Old 19th Nov 2018, 11:16 am   #10
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Default Re: Sanyo G-2601KCA - one channel audio

I ordered some BC546C's that someone suggested could be a good fit. Also other recommendations included the KSC1845 or ZTX1051A but they were not in stock. I will go to another store when I get a chance, but I'll first check the ones I ordered. I should have them tomorrow.

I checked in my parts bin, and found several transistors that seem to be a match. For example, C1815, C945 and S9014 all have specs that seem within limits and have hfe>500.
I'm tempted to give them a try, but then I'm afraid that I may cause more issues.
What do you think?
Also, what worries me is that the transistors in my parts bin are from ebay, I just got them to play with, and not really use them in mission critical situations...
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Old 19th Nov 2018, 1:57 pm   #11
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Default Re: Sanyo G-2601KCA - one channel audio

My Towers book suggest for the 2SC537 a BC347A

BC347A-Transistor-Silicon-NPN-Case-To92-Make-Motorola

There are some originals on E-Bay USA but you have to get 10.
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Old 19th Nov 2018, 3:23 pm   #12
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Default Re: Sanyo G-2601KCA - one channel audio

Thank you! I will check for those as well.
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Old 20th Nov 2018, 5:19 pm   #13
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Default Re: Sanyo G-2601KCA - one channel audio

And the search continues...
I swapped out the suspicious transistor, but the problem is still there, and I do get the same behaviour when I poke it with an insulated tool.
In the attached picture, this is Q2.
I tried to trace the incoming signal on both channels. The difference I found is that the right channel leaves the emitter of the transistor (Q4 in the pic) with a DC level added to it, while this is not the case for the left channel. I mean the signal has no dc component after it leaves Q2.
Also, I took some measurements with respect to ground on Q1 which is the transistor that receives the power for the board.
Left channel: Vc= 25.4, Vb = 6.6, Ve = 6
Right channel: Vc = 25.4, Vb = 3.2, Ve = 0,69

As you can understand, I am confused, and i'm not sure what to look for.
All capacitors are measuring fine, and all resistors also are within limits.
I have the schematic of the system that I have found in a post here, but it is too blurry to understand and I think it is a little cropped. I am attaching it in case any of you can share some advice!
Thank you
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Old 20th Nov 2018, 6:21 pm   #14
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Default Re: Sanyo G-2601KCA - one channel audio

I'm finding it difficult to read the diagram, but there is something wrong around, or with, the right channel Q4. A silicon transistor needs between ca. 0.5 & 0.7v between it's base and emitter to conduct and amplify. With those readings the B-E voltage of Q4(Right Channel) is a shade over 2.5v. The readings for Q4(left) appear to be correct.
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Old 20th Nov 2018, 6:39 pm   #15
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Default Re: Sanyo G-2601KCA - one channel audio

True, the diagram is almost useless, especially since I can't tell where's the signal input, and where the power comes from.

I just realised that I swapped the channel by mistake. The left channel is the one not working. I have edited the text. The measurements are correct.
My trouble is to find what is causing the wrong readings on the left channel. I was assuming an open component, but everything reads ok.
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Old 20th Nov 2018, 11:24 pm   #16
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Default Re: Sanyo G-2601KCA - one channel audio

Q4 (left) could be breaking down when powered. Replacing it with a known good, preferably new, transistor would prove this. Remember that the pin-outs of the replacement device will almost certainly differ from that of the original type.
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Old 21st Nov 2018, 7:09 am   #17
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Default Re: Sanyo G-2601KCA - one channel audio

I think I will replace all transistors of that channel
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Old 21st Nov 2018, 5:03 pm   #18
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Default Re: Sanyo G-2601KCA - one channel audio

I can pop a couple of 2SC1815 BL's in the post if you're still looking?
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Old 25th Nov 2018, 9:05 am   #19
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Default Re: Sanyo G-2601KCA - one channel audio

Thank you very much for you kind offer! I already have some C1815 available, and from I can tell they are (almost) identical. I'm realising that in many cases in transistor codes the initial digits may be omitted; am I right?
Can you educate me a little here?

As a side note, I've been battling with a nasty cold for almost a week now, and I did not have the chance to make any progress on my quest
Next week is also going to be really demanding as far as my day job is concerned, so I will be slow on responses and progress as well.
Just a heads up that I'm still around!
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Old 26th Nov 2018, 3:32 pm   #20
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Default Re: Sanyo G-2601KCA - one channel audio

Japanese transistors makers generally do leave off the 2S, unless the transistor is big enough to get the whole thing on.
Some do it with IC's as well.
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