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.
Separate names with a comma.