OK. I know I once had some of that de-soldering wick stuff, but so far I can't find it. Where should I look to buy replacements for those? I think it's obvious that they have leaked.
Yamaha R-50
- Thread starter Hamm
- Start date
Either that or someone spilled something in there.
What µf and voltage are they ? What diameter and length in mm are they ?
There is no sign of anything spilled on their tops or sides. Only seemingly coming out from underneath.
50v - 6800 UF
25mm dia - 50mm height.
Going to want to scrub that dark /crusty portion of the circuit board as clean as possible. Address any oxidation of component leads and jumper leads. Caused by the leakage.
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Pins 12 & 13 are the standout faulty results.
High pin 13 voltage may correspond to low current draw, ie an open.
I don't see a pin to pin test that would confirm the open. You could try
a diode test, red probe on pin 10 black probe on pin 14, amp powered off/unpluggesd, expect 2xVbe, 1.4V
Maybe others with better eyes will pick something up.
High pin 13 voltage may correspond to low current draw, ie an open.
I don't see a pin to pin test that would confirm the open. You could try
a diode test, red probe on pin 10 black probe on pin 14, amp powered off/unpluggesd, expect 2xVbe, 1.4V
Maybe others with better eyes will pick something up.
Well, I ordered the capacitors and wick from Mouser. They don't show having the STK, but other sites do. Should I order that as well? I'll try performing that diode test, but most of this goes right over my head. Baby steps. I mean, I do generally know what a diode does, but beyond that lies a dark abyss...
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Diode allows current flow in one direction (of the "arrow") and blocks flow in the reverse direction (hence the bar). They are multifunctional from providing a simple 0.65Vdc drop to bias transistor/Vbe tracking duties to rectification to ... Diode test (diode symbol on MM) is a common procedure for testing transistors. Nice graphic from markthefixer
Attachments
If you download a copy of the STK4873 datasheet you will find an equivalent circuit on page 2. The test was for pin 10 & 14 so looking at the equivalent circuit for a path between 10&14 you will see a b-e path via the VAS(?) transistor and another b-e path. If either of these transistors had failed then this would give you a different result, test is limited to the b-e junction, does not cover the c-e junction. I suspect that the vas transistor (with the cap) has failed c-e short(?) or maybe one of the driver transistors.
Years ago I messed with some of this type of thing after a neighbor guy gave me a Heathkit tuner he had built. I still have it. I believe one channel is out and I have some recollection of what component was suspect. I intend to look into that after I get through with this Yamaha (if).
Sparkplug
Super Member
The datasheet contains a logical/equivalent diagram of the STK. The transistors I mentioned are part of the STK "internals"
Get used to googling xxxx datasheet pdf
Oh, so not accessible. Got it. So is the STK fried, then? If so, can we deduce a cause? Could those bad/leaking caps be related? I have read that these STKs can be a bit fragile. Could it just fail with no outside cause? I was playing the system pretty loud, but I've done that many times. Was driving a pair of JBL control 1's. I believe they are 4 ohms. I have also read that this tuner/amp was/is good at driving low impedance loads, if that's the right way to say it.
I have seen this STK listed for sale. Is there a specific source I should use or are they all pretty much the same?
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audiotemp
Super Member
Is this what your speaker connections look like? (This is from thr R-50 user manual.)
Do you see where it says speakers should be 8 to 16 Ohms?
Who told you the R-50 could drive 4 Ohm speakers?
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