No. That's just what was there.
PS: It's crusty-looking, as if some liquid evaporated and left that crust behind.
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Yamaha R-50
- Thread starter Hamm
- Start date
PS: It's crusty-looking, as if some liquid evaporated and left that crust behind.
OK. Found them. They are larger/taller than most other resistors and are grey. On R346 I get a consistent .003 or .004 read on the 2v scale. However, on R345 I can't get a consistent reading. It will jump to high numbers such as .3v or .8v or a full 3v or 4v or 14v or 18v and then immediately drop back to no reading at all. It's all over the place, or won't read at all.
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OK, problem with left channel.
Measure dc voltage at connector white(?) wire LO marked in red OR either sider of R307.
Also measure at either side of R319, marked in blue.
Voltages stable? or bouncing around?
Attachments
OK. Nothing is labelled or laid out like the diagram, but the 3-pin white connector I believe is the right one has red and white wires on either end. Not marked LO or RO, but each one reads .005 to .006. There are 5 resistors in the area where I believe R319 must live. Each one reads a steady .005.
OK. I wondered about that. Some things did seem mirrored. Still, there are no numbers for any of my resistors. I was going by numbers shown for other nearby components.
PS: After considering the mirror image situation, I feel confident that I located R319. It reads .005.
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OK, the point to those measurements was to check if the voltage variations were due to an earlier stage, ie, bs in bs out,
Need to take a closer look at the STK, need to measure the dc voltage at each pin and note if the voltage is stable or if it bounces around, try to give range eg, 2.2-3.1V...
Don't attempt to probe the STK pins, you will slip and fry the STK. I haven't worked on an R-xxx, hopefully it has a removable base plate, best to probe from the solder side, ie, identify pin #1 and follow the track to a safe measurement point/solder blob, repeat for pin 2 etc...
If you can't easily access the solder side then the alternative method is to probe a connected part, eg, looking at the schematic, notice that pin #1 is also connected to C241, R323, C235, C239, these parts are connected to the same node, test at any of these parts is the same as pin #1. Testing at R323 is probably easiest since the legs are exposed.
Again, don't probe STK legs, note Vdc at each pin and if it's stable.
Measurements completed. I am unsure whether there are 15 pins or 16. There is one solder point at the end of the line which looks different than the rest. I am also unsure which end is pin #1. ALL READINGS WERE STEADY. Looking from the back side of the board, and starting on the right end, with the front of the unit facing me, the first soldered connection in that line is the odd-looking one, but I measured it too. It reads 1.09v. If there are only 15 pins, then I'll call the next one pin 1- 10.15v; pin 2- 34.7; pin 3- 33.6; pin 4- 40.4; pin 5- 40.2; pin 6- 36.2; pin 7- 40.6; pin 8- no reading; pin 9- 40.5; pin 10- 40.2; pin 11- no reading; pin 12- 1.3; pin 13- 35; pin 14- .4; pin 15- .4.
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Might want to lift those large caps and see if one of them vented.
By lift, do you mean unsolder them? It certainly seems to me that stuff came out of both of them. The crusty stuff is all around both of them. It looks like they were both originally glued down. Not sure how tenacious that glue might still be.
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I didn't pay attention to that, but I can get those tomorrow.
Then I numbered the pins wrong in my description, but I still don't know which end to call pin 1. It faces the back. The heat sink stuff is toward the front.
PS: On another thread here I found out how the pins are numbered. It says "from left to right". I'll re-do my measurements tomorrow with the correct pin numbering and note all polarities.
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Yes.. The only way to inspect the underside.. It is likely no longer glue..
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audiotemp
Super Member
In a correctly operating STK4873, pins 5, 8, and 12 should all be at essentially zero DC volts. Pins 5 and 12 are the amp outputs (hence, they will be within a few 10's of mV of ground) and pin 8 is hardwired to chassis ground (and so should be exactly zero, within the accuracy of your meter). The correct numbering of the pins must give pin 8 at zero volts.
I think the pin numbering on the PCB diagram (the "1" and "16" at either end of the row of STK pins in the pic in post #23) is backwards and most of the STK pin numbers in the schematic are wrong (in a way that matches up with the wrong PCB numbering). So I think when you number correctly things will no longer agree with the SM. I think pin 12 connects to R345 via 0.47 Ohm R337 but it's late so do your own checking on the pin numbering.
In any case, it appears you have one STK output at rail voltage, which isn't good.
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Revised measurements are in. The two I thought had no reading before were because I was on the wrong scale- I'm learning...
Pin#
1 -.37
2 -.4
3 35
4 -1.3
5 Jumping from -.002 to -.006
6 -40
7 -40.2
8 -.006
9 40.2
10 35.9
11 -40
12 -40
13 33.2
14 34.4
15 -10.1
16 -1.0
Pin#
1 -.37
2 -.4
3 35
4 -1.3
5 Jumping from -.002 to -.006
6 -40
7 -40.2
8 -.006
9 40.2
10 35.9
11 -40
12 -40
13 33.2
14 34.4
15 -10.1
16 -1.0
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