Beau Geste
Italia
Beware, sometimes the Mtester fails in measurement .Maybe for some contact problem.
Finally we're now on a new page, have a nice lunchyou're welcome guys
Happy to get to page 9, I can't have lunch/dinner and checking this thread seeing at first the photo in post 141
We need to start calling you Professor!In-circuit transistor testing is exactly that: very difficult. The surrounding circuit poses low-resistance bypasses, capacitances, etc, fooling your transistor tester. For that reason, I always pull any transistor under test.
I made the following sketch to give an overview of the transistor symbols that Yamaha uses.
DISCLAIMER: this applies only to traditional Japanese TO-92 transistors (2S prefix).
View attachment 1092609
On the left side the rectangular 3-block symbol as printed on the PCB layout drawings in the service manuals. The black-shaded block on the left always denotes the emitter. This is important to know as this symbol presents the right transistor orientation regardless of the transistor format (TO-92, SOT-33, SC-38, TO-126, TO-220, etc.)
Now, if life was perfect and logic.... they would have printed the same symbol on the real PCB's..... but oh no.... that would be too easy...
Instead they printed either two "TO-92 footprint style" symbols on the PCB, even if the transistor to be installed is not a TO-92 device....
The only good thing about the TO-92 shaped symbols is that the black-shaded means a PNP device (so always a 2SA or 2SB), and the non-shaded always means an NPN device (so always a 2SC or 2SD). This will allow you to quickly and securely verify if you did not make a PNP or NPN mistake.
However, it does NOT allow you to verify if the transistor concerned is actually correctly installed (a mistake often made).
If we take standard traditional Japanese transistors (2S designation) then the ECB leg orientation for TO-92 and TO-126 transistor is indeed ECB as shown above.
I prefer to say: when looking at the printed surface with legs down. Which makes it easier to state that the default leg orientation for TO-220 transistors is the opposite: BCE.
This is why the TO-92 symbol printed on the PCB for TR712/715 is 180 degrees turned (or why the TO-220 devices are turned around 180 degrees, whatever you prefer)
Now, the CR-1020/2020 is a massive party of small signal transistors that are different from standard TO-92 devices. These are the small transistors with a flat rectangular body, which are:
2SA673A
2SA844
2SC1213A
2SC458
Which are so-called SC-38 or SOT-33 housings, and which have a reverse ECB leg orientation ! That's why they are installed with the printed text backwards with respect to the TO-92 symbol printed on the PCB. Hence, be aware that modern subs are most likely installed inverse of those (inline with the printed TO-92 symbols).
So far so good, no issue to install modern TO-92 devices, you may think.
Well.... there is one showstopper in these Yamaha units (and also in other Yamaha units like the CA-1010/2010): bias temperature tracker TR608.
View attachment 1092610
This transistor, an SC-38 shaped 2SC458, was deliberately chosen for its flat surface, so that it can make a good contact with the heatsink. Indeed, the flat surface of TO-92 device could do as well, no problem, besides that Yamaha laid out the PCB for a SC-38 device, hence the PCB ECB holes are in the wrong direction for using a true TO-92 device.
Only two options:
1) Keep the original transistor in
2) Use a TO-126 style transistor (installed with its back side to the heatsink surface)
Important: it must be a TO-126 transistor without a bare metal back side, or else the collector will be shorted to the heatsink.
Most suitable TO-126 transistor for this is the 2SC3503 (KSC3503), like this (the legs are Z-shaped to create the right offset from the board):
EDIT: the CA-1010/2010 uses a PNP in this case, i.e. 2SA1381 (KSA1381)
View attachment 1092612
One last note on two specific modern TO-92 devices that we use regularly:
KSC945C/KSA733C
KSC1008C/KSA708C
The C-suffix does not denote the Hfe ranking but the leg orientation. Fairchild makes them in C-version and in non-C version; make sure to order the C-version (which means center collector), or else it will go really wrong at power-up !
**********
And a bit more feedback on your last post: TR611 is a BJT, not a FET.
As you may notice on the PCB layout drawing that TR611/612 are shown with the transistor below the heatsink as where the transistors in your unit are installed inside the heatsink.
That is because TO-220 devices (2SC1624/2SA814) were installed in many cases, requiring the transistors to be 'belly down' with heat sink outside on top.
The ECB orientation of TO-126 devices (as in your unit) is the reverse of TO-220 devices, so they are installed 'belly up' and therefore inside the heatsink.
Excellent subs are the (obsolete) Hitachi 2SD669(A)/2SB649(A), but hard to find guaranteed genuine ones these days. But as I mentioned before, there are since very recently new subs for those on the market: Toshiba TTC004B and TTA004B.
In-circuit transistor testing is exactly that: very difficult. The surrounding circuit poses low-resistance bypasses, capacitances, etc, fooling your transistor tester. For that reason, I always pull any transistor under test.
none of it was aimed at you.please give me some feedback on "thread etiquette."
LOL Mmmm Mmmm good.I think Avionic ruined everyone's lunch with page 8. Hint: what do you see at the top of page 8?
none of it was aimed at you.
I think Avionic ruined everyone's lunch with page 8. Hint: what do you see at the top of page 8?
I might add a warning here:2) Turn around to the component side and do a general flux release and gently brush around (PCB + parts)
You'll be surprised how shiny your stuff will be
Give us some before-after photos
you mean something like this???
this should open your apetite
Seen that before..
learned from the bestThanks Pete, that's an excellent example !
Your custom heatsink is nice; but don't forget to have electrical isolation between the TO-220 transistors and the heatsink.
don't be shy to put the entire remaining chassis in the shower and give it a good soap and rinse.
I'm having some difficulty "wrapping my head" around this concept but I'll go with it. No Mr. Proper available here but I'm sure another oven cleaner will perform similarly. My larger concern involves determining what I would need to isolate from the water. I'll remove the faceplate and knobs, but take a look at the photo below and let me know if there is anything more I need to know before putting the dam thing in the shower!
I bet you see that alot. You got a dirty job my friend
Seen that before..