Need help with Sanyo 6CA-T45 (radio not working)

[Johan de Jong]

I got a nice Sanyo 6CA-T45 that needs repair. The clock is working fine, but I can't get any sound from the radio nor the buzzer.
Now I'm not so good with electronics, so I could use some help.
This is what I tried until now:
- I looked for any loose wires but could not find any.
- Contact cleaned all switches and the volume potmeter.
- Measured the switches and the potmeter and they seem to be doing what they should.
- Checked that the transformer is working: it outputs 14V AC to the small switchboard.
- The speaker seems to be working. A click is audible at the moment I push the radio button.
- Double checked with a headphone (it has a 3.5mm jack) with the same result.

Now I don't know what else to try or to check.
Any suggestions?

[Guest]

Check if the speaker is REALLY working. Detach positive and negative on the speaker and do an ohm check with a multimeter. The speaker may have the rating printed on the back of the speaker.

Speakers can still be bad and make "some" noise". Just a hunch! Maybe swap with another temporarily, if you can, for testing.

Also, with the radio on and attempting to make sound, press on the tuner and switching board with something non-conductive, like a pencil. This may reveal if there are any cracked solder joints causing connectivity issues.

[Guest]

How did you check the switches and potentiometers? If you checked them in-circuit, you may get skewed readings from other components upstream/downstream that are interconnected to them. It is doubtful the switches are bad. It can happen, but would be rare.

So, if all else seems to be working, then it could be some bad capacitors or maybe a semiconductor. It looks like this is an AM-only radio so replacing any of those items would be quite easy.

[Johan de Jong]

Thanks Engineer for the helpful advice!

No success yet, but at least I could rule out more possible issues.
I checked the speaker. It says 16 Ohm at the back and I measure 16.5, so that seems to be ok.
You are right about the switches that I might get readings via other connections. But I think if I see a significant change between the open and closed state, and the resistance in the closed state is zero, I can be confident that the switch is working. I double checked all switches and they seem to be working. Same for the potentiometer.
Also poked around with a wooden stick, but it stays completely silent.

Regarding the bad capacitors or semiconductors, there are quite a bunch of them, so I really don't know where to start.
I'll make some better pictures after the weekend. Maybe you can spot something that I missed.

[Johan de Jong]

Made some more detailed foto's. While doing so I noticed in the first foto that two of the tracks on the small circuit board were interrupted. Maybe someone crossed these out intentionally? I'm not sure. I repaired them as well as two wires that broke off due to my own (mis)handling, but alas, still no sound. Not the radio nor the buzzer.
Can you spot anything suspicious?

I'm getting close to accepting that this wil be a clock without a radio. I was not really gonna use that AM radio anyway but it just hurts my pride

[Guest]

Hmm, no clue why those traces were cut out. I would like to find a schematic to see if it is noted there.

Anyhow, nothing besides that looks to be out of sorts. There are only 4 capacitors and 3 transistors (looking like early Germanium metal can type) on the tuner board and 2 capacitors and one dual-diode on the switch board.

You could do a little trick. To see if the oscillator is functioning you can take another working AM radio and tune it in between a station so there is just static and no signal and then place it directly on top of the tuner of the "dead" radio. Then power up the "dead" radio and go through stations of that dead unit and if the radio portion is still functioning it will bleed into the "good" radio's speaker that is sitting in between stations. It is like a wireless transmit from one to the other.

That way you can tell if the dead one is still pulling in signals and there is a problem with it getting to the speaker.

[Johan de Jong]

I tried your trick and it worked!
I put the working radio in between stations, switched on the "dead" one and tuned it until a very faint, but unmistakable Supertramp song came through the working radio! Amazing trick!
So my tuner is working and there still is some hope. I searched for a circuit diagram but could not find any. I'll see whether I can reverse engineer it. To be continued...

[Guest]

Ok, so that means the tuner is working. This is good. So, this might indicate the possibility of a bad cap and/or transistor. The transistor handling amplification could be faulty.

I am pretty sure I see 3 of them. One is marked Sanyo and starts with 2SB...

If we can ID those then I can look up a crossover equivalent. This is a low-power tuner so it isn't common for a semiconductor to fail so I would at least try to replace the 4 or 5 capacitors, if you can. They could be dried out and possibly dead-shorted. Caps and transistors are very inexpensive.

[Guest]

I think I found the transistor layout for this model. I actually have these (NOS) in my parts bin!

2SA101 PNP
2SB186 PNP
2SB187 PNP (May be 2 of these)
1S188 DIODE (1N60 will work)

I doubt the diode is bad. This radio also seems to have been a European model only. Not seeing anything in the US that was an equivalent.

First thing I would do is replace caps. They are easy to source. Get the same values in uf (microfarad) and voltage can be the same or a little higher. Never go lower in voltage. For example, I see that Sanyo 220uf 12.5v. You can replace with 220uf 16v, 20, 25v.

[Johan de Jong]

Oh this is fantastic! That diagram is very useful. I will check how the diagram matches the components on the boards. And then find out the specs of the capacitors and order them. As well as the transistors and diode. And then start replacing them until this radio gets back to life. This all may take a while but I'll let you know how when there is progress.

Many thanks Engineer, you are of great help!

[Johan de Jong]

I replaced all 6 capacitors, but no succes yet.
To be sure I did make things worse, I did the test with the second radio again, and that still worked.

So now I would like to replace the transistors and maybe also the diode.
I checked the transistors on the board and these are indeed:
2SA101 PNP
2SB186 PNP
2SB187 PNP (2 of these)

My big question is now: how to find the correct equivalent transistors to use? I did some online studying, but I still have no clue how to pick one.
I usually buy at Conrad.com (or .nl actually): https://www.conrad.com/search?ATT_LO...chType=suggest

[Guest]

Believe it or not you can probably find NOS originals on Ebay. These transistors go back to the early 60s and so are positively ANCIENT.

I will have to look at their specs and see if something relatively modern can be a crossover. I think I have some here. IF I do I can post some to you. I will check.