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Yamaha cr-200

J

JonathanW

New Member
Hello Everyone,

Could I please have some help with a Yamaha CR-200 I have had it for about 20 years, I am assuming it's a circa 1975 build?. Its been working with no problems all this time but recently I have noticed a crackle from the right speaker, then without warning the crackle went full volume.

I can only describe this crackle as not a hum like 50/60hz although with everything disconnected from all inputs etc with the volume up high you hear earth like hum, anyhow I digress the crack sounds like dust on a vinyl record or a crackly pot however with the volume down to zero this crackle remains audible and as mentioned it sometimes goes full volume without warning

I have cleaned all the volume, bass, treble pots with servicesol super 10, and cleaned the speaker switches etc. Inside I can't see any bad capacitors or any sign of any component that has burned out!

The caps are original as far as I know or have certainly not be changed since I have owned it. It gets daily use so I am considering changing the lot.

Any ideas of what can be causing this will be greatly recieved.


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Welcome aboard... Need to see some interior photos of the amplifier area. Crackling and popping could be solder connections or transistor break down.
 
Remove the two 2200µf Capacitors and inspect the underside for leakage

4xkv0Hv.jpg
 
@avionic I have removed both they had no signs of leakage etc but I have now replaced them anyway. someone mentioned it could be the transistors in the preamp apparently A561, C734, A763 does this sound plausible? I can't find them online and am unsure of how to find equivalents can anyone shed light on this?
 
(2S)A561, (2S)C734, (2S)A763

These are probably the small black signal transistors. Most of the time, these are the one's which cause the static and popping problems with volume down and nothing playing.
 
Wow thank you @avionic ! Ive struggled to find them I will get on this and get them ordered, once they are in do i have to readjust the bias controls or leave them where they are?
 
I have found this for the test points can I confirm 25mv or 33mv?

I am assuming this is set with nothing connected to any source?

mbz said:
Maybe help with the easy stuff.
Working from CR-200E SM.

Bias test points
Left channel, TP2(+ve probe), TP1(-ve) R429 , 0.22ohms, adj VR401
Right channel, TP4(+ve probe), TP3(-ve) R430 , 0.22ohms, adj VR402
Click to expand...
 
No change required unless the outputs are suspect faulty. Just pointing out that this
is an earlier design using NPN(only) outputs. Most amps of this vintage use a PNP and
NPN complementary pair of outputs. Also it is quite different from the CR-200E (sm).

Check the bias by measuring the dc voltage at the test points (posts) highlighted.
This corresponds to the large white resistor, 0.22ohms, as a guess expect 6-10mV
(27-45mA).
upload_2021-8-4_18-57-17.png
 
I have now replaced the transistors and replaced them for the below section, the crackle has now gone for good I also replaced most of the capacitors and it seems a lot quieter now (less noise floor not output volume)
I have set the Bias at 20mv after 30mins of nothing playing the heatsink is warm about 35°c 95°f should I push higher for say 25mv?

2SA561 -- KSA1013YTA
2SC734 -- KSC2383YTA
2SA763 -- KSA1015YTA
 
To summarise what had been done :

Also thank's to @avionic @mbz @cademan for their help in this matter.

As I mentioned earlier in the thread, I have a circa 1974-1978 Yamaha CR-200 natural sound stereo receiver, I have had it for about 20 years, and gets daily use, so I wanted to repair it and give it a new lease of life.

The service manual I found was for the Yamaha CR-200E, and from what I have been told it is slightly different but it's useful for reference. https://www.manualslib.com/manual/814073/Yamaha-Cr-200e.html#product-CR-200E

FAULT:
The initial fault was a static crackle on the right channel that would occasionally go full volume without warning, other things were dirty pots, high noise floor, and an earth hum.

Repair:
The first thing: was to clean all pots, Volume, Bass, Treble, Balance, to do this I used Servicesol super 10 switch cleaning lubricant that worked well just be careful where you spray it as it makes a mess.

The second thing: I replaced the capacitors as they were original, only for the preamp, amp, eq (not the tuner section, I may replace these later but the tuner is fantastic and sounds amazing, it finds stations I never knew existed).

Capacitors:
1x 50v 3300uf,
2x 50v 2200uf
1x 50v 220uf
3x 35v 220uf
2x 6.3v 470uf
1x 16v 220uf
2x 25v 220uf
4x 25v 47uf
1x 50v 10uf
2x 16v 47uf
4x 25v 4.7uf
2x 16v 10uf
2x 25v 10uf
4x 50v 0.22uf
4x 50v 0.47uf
Total caps: 31

Amazing how small they have become over 45 years!

Before:
Oa10Kr1.jpg


After:
A8WdFV8.jpg
EFTrKuM.jpg


The third thing was the transistors only for the eq and preamp section.

Transistors:
4x 2SC1571 -- replaced with 2SC3198
4x 2SC734 -- replaced with KSC2383YTA
2x 2SA561 -- replaced with KSA1013YTA
2x 2SA763 -- replaced with KSA1015YTA

The main output stage has not been touched.

U5BUWWZ.jpg


Setting the Bias at the test points to 10mv each:

I found setting both to 10mv with nothing connected and no music playing just at idle, after 30 mins the heatsink would be 5-10°c 41-50°f above current room temperature:

EsVefCv.jpg


Left channel, TP2(+ve probe), TP1(-ve) R429 , 0.22ohms, adj VR401
Right channel, TP4(+ve probe), TP3(-ve) R430 , 0.22ohms, adj VR402

In truth, I found these would wander a little I set to 10mv but did see 9.6-11.2mv but the heatsink remained at a sensible temperature.

Conclusion:

After cleaning the pots I have nice smooth volume, bass, treble, and balance controls, I did also clean the loudness, source, and speaker selectors with the same stuff.

The replacement of the capacitors has silenced the earth hum sound.

The transistor replacement has brought the noise floor down to a minimum and the static crackle has gone.

The sound quality is now warmer and the treble really sparkles again, so worth the money and time!

Pride of place:

wqr0EeS.jpg


Once again a big thank you to all who helped!
 
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