Discussion in 'Yamaha' started by LFazio51, Nov 25, 2017.
Damn.. Enough dirt in there to plant potatoes.
Quote of the Day: "Change is the end result of all true learning!"
@Oilmaster Thanks for the education involving the original power transistors. I started a Thread in DIY to gain some additional insight and you've confirmed what several have mentioned. It's funny how one can engage in so much research and STILL not get the true picture. I thought that these trannies would show some similar hFE measurements based on all I've learned but never considered the conditions for which they were being tested. And again, the educational aspect of this hobby is both remarkable and fascinating!
Main Amplifier Control Board
I will definitely put these new transistors on my list
Main PSU Control Board 1 - Transistors
I'll order this one as well but am concerned about the other small transistors and would love to get someone to comment about them as I DO NOT want to have to replace any after I've completed the project. I would like to identify any "bad actors" that are known issues and should be replaced. I've listed them below for anyone that would like to comment on this request.
Yes, potatoes, spinach, and squash!
I'm also open to any advice/comments on cleaning as well.
See this excellent effort by @rottalpha (hail hail) on general transistor substitutes; suggest to add this to your watched threads list
Things you always have to validate for yourself:
1) Is the in-circuit voltage (including signal swings) across emitter and collector (i.e. Vce) higher than the allowable Vce (start downloading datasheets into a dedicated archive)
2) Is the in-circuit current above the maximum allowable collector current (i.e. Ic). Simplified calculations using only real resistor values between known voltage rails will do)
3) Never make the mistake to think bigger-is-better, as that often adds unwanted properties into a circuit.
And a whole bunch of other things, but the above being mandatory.
I will point out special cases if any.
Dang! Waht a NEWB I AM!! I tried to keep from bothering everyone and spent a few hours researching AK threads and the database, but couldn't find anything! I did run across some excellent threads on 2020/1020's that many of you participated and I've definitely "watched" them. I'll take a look at the link but since you've not recommended any specific ones from the list that are typically "known bad actors," I feel a little better.
I think I'm going to be severely "hamstrung" in the transistor area as I don't believe I have enough knowledge to preform the mandatory tasks you've mentioned. I'll have to dig into some serious research just to understand much of what you've said, SO, lot's more learning to do for ME!
No worries; AK has grown so big that it can take hours to find things back.
Just giving you and others simple directions; but from there you'll have to graze the grass a bit yourself
Otherwise this thread is (too) soon over in a few more posts
No panic to get a PHD in transistor science; Pete's list will help you a lot.
I couldn't agree more, I need to shorten my posts and take a little "wind out of these bagpipes!"
@avionic - The cancer has been irradicated! Freshly coated end-bells!
I'll bet those bolts were fun to remove with all that resin all over them.
Actually no; the resin is not "tacky" so there was really no adhesion to them. lol! I'm coming to learn It's always a "good thang" to focus on the positives with this project.
Getting ready to take transistor measurements tonight on the L.CH main amp board.
Good afternoon all. Been busy testing transistors on the L.Ch. Main Amp Board and have run into some confusion that's prohibiting further testing of TR607 (2SA844) PNP transistor. It seems that on the original spec sheet, that case style is slightly different than the 2SA844 installed, creating some confusion when trying to determine the pin positions. The photo below is an example. (FYI - I've only been able to locate what appears to be the original Hitachi 2SA844 spec sheet - maybe there are others but I've not been able to locate them). If someone can provide some much needed guidance on the orientation of these pins it would be greatly appreciated.
There are a few transistors like that old style "outhouse" TO-92.
Assuming the OEM transistor is installed correctly. Center pin is the collector. Look at the circuit trace. Emitter of TR607 is connected to the pos. side of C613. The Base is connected to the center collector pin of TR608.
Thanks - I got it now!
Main Amp C. Board Transistor Measurements - In an effort to educate myself and identify any potential problem transistors, I've researched several threads and have tested the transistors with (3) devices; a Uni-T 61e, Fluke 787, and the inexpensive e-Bay MTester in an attempt to glean some insight into their current disposition. After reading many threads, I realize this is by no means perfect while while in-circuit but there is no other higher quality means available. I'm hoping that with your assistance, we may be able to "glean" some insight and identify any that may seem suspect. Once complete, I will then remove for further testing.
I believe I've performed these tests correctly as I do believe all pin positions were validated, both by schematic and visual inspection of the board. I created a PDF of the pin positions of the board layout and attached for review. If anyone can see an issue, please let me know. I feel this will be helpful for a "Newb" if I have to replace any of these.
The photo below illustrates the equipment used to test in case anyone isn't familiar.
My first pass of testing was performed with the MTester (device on the right above) using (3) leads. It returns the pin position along with hFE and Uv. It also provides a nice little diagram on the read-out (see pic below). These values have been document but not shared in this post. I will share if necessary but it's a lot of information and it may not be necessary until I receive some feedback on this post. With that said, this initial test returned some interesting results and has caused me to question its capabilities. An example of this would be the results for TR611 (2SC1212 B) - Original spec sheets show this to be an NPN with TR612 (2SA743 B), its compliment to be a PNP. I've tested TR611/612 twice, on separate days and each time it returns TR611 as a JFET! (see photo below
TR611 - MTester Results
TR612 - MTester Results
After the first pass, I noticed that it would not register a reading for TR604, 605, and 607, so I decided to test these three transistors with the Uni-T, Fluke, and MTester (diode method). The photo below illustrates the results.
Measurements using a DMM under diode settings
The MTester continues to return some weird results using the Diode function. The screen shots below represent those measurements where you see "2-Diodes" and "Resistor" in the data sheet above.
It seems to me that there is some consistency between the Uni-T and Fluke measurements but not so much with the MTester. The MTester also seems to be failing to properly identify the pin positions with respect to the schematic and board layout. This may be due to several reasons, not the least of which may be "in-circuit" issues as I've used for capacitors after removal and all seems to match with my DMM.
In conclusion, it seems as if TR605 and TR607 may definitely be bad, especially TR605 "base to emitter" tests where I'm not only getting a small reading but a "beep" as well. When time permits, I'd love to acquire some feedback on these measurements so I can continue moving forward. Thanks everyone and have a Great evening.
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).
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:
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.
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)
One last note on two specific modern TO-92 devices that we use regularly:
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.
Great explanation as alway, thx!
That was a very useful post Oilmaster, regardless of which amp one is working on.
you'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
Separate names with a comma.