I had exactly the same thing trip me up on a Pioneer SX-1980! Now I use a cheap transistor tester to verify the pin-out of the old transistor and the new one I'm putting in. This also saves me from silk screen mistakes on the board and me grabbing an incorrect transistor when I think its the correct one :)
Hi. One thing I like to do is get a red and black fine-tip sharpie marker. Before removing a transistor from the board, I mark the base with a small red dot if NPN, or a small black dot if PNP. Then, I’ll mark the emitter with a larger dot of the same color, and no dot for the collector. Once I’ve got a replacement, I’ll put it in one of those testers (I have the Peak Atlas DCA55, but there are others) to make a quick check if the replacement is good and to identify the pinout. Then I’ll mark the base lead with a small dot right where the lead comes out of the package, and the emitter with the same-colored dot, but further down where the lead has a “bump”, or changes width (like with a TO-220 package). Again, red for NPN and black for PNP. With both the transistor and the PCB marked, you can quickly tell if you put a PNP where an NPN should go (or vice versa), or if the pins are in the correct holes! HTH. 😊
The problem issues with their fixes are the most valuable part for me, so you fixed it and put it back together flawlessly you thought and it doesn't work, now what? Thanks Tony!
I'm sure your excited about getting this beautiful Receiver up and running. Sometimes we all make simple mistakes during these times. But I enjoy the mistake videos, you actually learn more. Thankyou
@ 14:35 , I was reading a service manual on a old Sherwood S7210 Receiver, page 4 (as a prospective purchase), and for instructions on setting the bias, 3 methods of bias calibration were described, one using a THD meter at the output, another using a IMD meter, and the third was to monitor the line power current, they suggested that monitoring the line current going in with the amp on, no signal, and bias controls both turned down, it was acceptable to adjust the bias until a slight increase in line power wattage was measured on each channel. @ 25:14 , The base connection of the protection transistors Q3 and Q8 seem to be at a point where they monitor the Q3 and Q6 driver transistors output current, but that is different from a lot of other amp designs I've seen where that base connection is on an emitter connection of one of the output transistors, which makes more sense to me, as it will do a better job of monitoring the actual current output of the amp instead of monitoring it at an intermediate stage that can't sense what may be going on at the speaker terminals.
Wasn't it brilliant to not label the prefix on transistors so you don't know if you are looking at a 2SA733 or KSA733? And of course why not change the pin out! I've always hated how a transistor is labeled as A733, etc. Just put the whole number! I'm sure this has tripped up many experienced techs and weekend techs too! Great series!
I have worked on amps since my teenage years, never restore, just repair. Many times i had the wrong parts with different lead config, and i always checked and double checked with a meter. I was too scared of blowing things up and i was doing it to make money. I didn't know of dim bulb testing back then too. I rarely.made those type mistakes. I think c to e conducted one way so i used that to determine those 2. Been so many years.
Hi Tony, thank you so much for showing the troubleshooting process. I really like your "keep calm and measure" approach to tracking down the sort of errors we all come up against. I am working a bit further down the ladder on an SX-750, sorting the case and a relay to ease the load on the power switch before I move on to the amplifier electronics. I am enjoying the process very much and am continually learning from your videos.
The Tony Syndrome strikes again! 😲 That’s pretty nasty that they change the pinout on those transistors. I would be popping them in my little tester before installing just to make sure the EBC are where I expect them to be.
The first clue was the slow DC offset drop at initial turn on. Shortening t-shooting time is what I’m all about because I’m not making videos. If I was, I couldn’t take the heat of moron commenters like myself telling me how to do it faster 😂. Thanks for what you do!
In those days people didn't use super accurate DMM's for adjusting within 1% of the "ideal" value... if the meter was about in the ball-park the settings were OK.. meaning less than 50mV off-set (unaudible click) and bias within a couple of mv of the "ideal" setting. So, yes... adjustment was possible.
In my experience, it was much more difficult to adjust to even "good enough" specs. With a single turn pot (that only had about 300 degrees of actual rotation), just barely moving the pot made a huge jump in voltage. I replaced a lot of output transistors because those pots changed "just a little" and the bias shot way up. It's a much easier process with a 10-turn pot.
I have scratched my head for hours over this 'C' notation before as I had it with the 2N5401C and the 2N5401 also its complement. The parts are identical but one has collector ('C') in the middle one does not the and the nearest I can get to an answer to this is that the manufacturers of PCBs prefer the collector in the middle and some don't !! Anybody know why the two exist ?....cheers.
No lesson like a hard lesson... On the bright side you drilled into us to check pinout, and compare to original, along with whats printed on the board. I have been writing on the bag or the ammo strip the pinouts, so no chance of using my non existent memory.
