The Last Transistor, and associated "extra" components, has been replaced. I verified my work with a checklist, and it's very close to being powered up. I have some tidying up to do, along with cleaning the soldering flux off the back of the PA Board, and I'll do that tomorrow with fresh eyes.
And I finally bought a decent workbench for the garage. Now I have a place to mount a proper bench vise, belt/disc sander, bench grinder, and a drill press.
Stand by for pix!
And for my friend SiG, 19% humidity!
Just gorgeous today, and I'm out in the garage painting some small parts, and dropping the exhaust manifold off the Supra so I can get at some bolts located behind it. Good thing I decided to do this, as three of the seven bolts were almost "Finger Loose", and the two end ports were blowing exhaust out. The other four bolts came out very easily, and were soon to be loose. The manifold is mounted on studs screwed into the cylinder head, and "Prevailing Torque" nuts hold it to the studs. All seven studs came out, but the nuts stayed on them. I'm having a difficult time getting the nuts off the studs, and might just buy new ones, as they're still available from Toyota.
The infamous Last Transistor for the Fisher RS-2010 got here yesterday, so I'll be installing those later today. I saved these two for last as they have an "extra" transistor (NOT on the schematic diagram) just "scabbed in there", and I still have to document what number transistor it is, and exactly how it's connected.
Hope you enjoy the upcoming weekend, as March will be going out next week accompanied by rain and snow here.
Keep your head on a swivel, as with the warmer weather coming, things might get spicy....!
Yow, this receiver was a gen-you-ine PITA to source the parts for. There are two transistors in each of the two Power Amplifiers. They're what's called a Complementary Pair, which means one is a PNP type, and the other is an NPN type, and their characteristics are matched to each other. There are several part numbers for each pair, -BUT- while I could easily find one of the pair, the other one was nowhere to be found for any of the suitable parts I was searching for. I was finally able to hook up with a forum member who had purchased a large number of these when they were still available, and after contacting him he agreed to sell me TEN of each type I needed.
So I now have enough of the correct parts to finish the Power Amplifiers, and have some spares for future use.
She's 40 years old this month. I go by the door tag that says she was built in March, 1985, but I've never tried to dig deeper to see when she was built in March. Toyota could most likely tell, but they're not saying.
She has an interesting story.......
I bought her and drove her home on New Year's Eve, 2012, so I've really had her about 12 years and a few months. I looked at about a dozen of them, and all of them either had a rod knock, rust holes you could put your fist through, trashed interiors that looked like they'd held raccoon fights, really bad body work, missing parts, or all of the above.
She was owned by the original purchaser for 27 years, and mostly had the typical maintenance a Toyota gets. She came with a shoe box full of receipts, so I was able to determine when some of the parts had been replaced, but I considered it a spotty record at best.
The original owners lived in Redlands, CA which is in San Bernardino County, which is a very dry, hot area, so NO RUST! They sold her to a single Mom who bought it as a bribe for her teenage son. If he finished High School, got his Driver's License, and a job, she would have given him the car and taken care of the maintenance, insurance, and licensing. Needless to say, that didn't happen, so she sold it to the guy I bought it from.
He said he'd bought it "To Restore", but judging from the JDM Honda Civic he drove up in, I doubt it. He said he was being forced to sell it because his girlfriend squawked about having to park her brand new Accord in the street, while his two off-road trucks, his three motorcycles, his boat and trailer, and his two other Honda Civics were taking up all the parking spaces at their place. He wanted $3500 for her, and while he said he knew I'd take excellent car of the and fix it up, nut if I wouldn't pay the price, he had "Ten kids lined up who wanted to buy it and drift it".
OUCH! A fate worse than death for these cars!
So I coughed up the Benjamins, and brought her home.
It's been a fun ride!
Yeah, it's been a few weeks, and a busy time it was with the gorgeous weather we've had for the last week.
And then I got clobbered with the cold/flu/whatever. Anywhoo...feeling much better.
Back to the Fisher RS-2010 Stereo Receiver I've now had almost a year. Yes, I'm embarrassed, but it turned out to be a LOT more work than I estimated. I'm now down to searching for ONE transistor, with all the rest having been sourced, and on-hand. The issue is that it's one of what's called a Complementary Pair, and while a sub for one of the two is readily available, it's compliment is not. Soooo....I have to dive into either finding a vendor with some in stock (NO eBay or Amazon....too many fake parts!), -OR- start going through the "sub-for-the-sub" routine, and find a complementary pair that's available.
Bags of new transistors awaiting their long overdue compatriot.
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It gets a bit tedious....
So what killed several transistors, and let the smoke out of three resistors? Who did the dirty, dastardly, despicable deed?
'Twas a shorted Zener Diode, it was.... that's what who dunnit!
The diode in question is labeled "DO6" in this clip:
In this application it's being used to develop a voltage which is 12 Volts less than the supply voltage, rather than developing "just" 12 Volts. They do this because the entire amplifier is isolated from "DC Ground", and floats between the +60 Volt and -60 Volt power supplies. The only transistor in this circuit connected to the chassis, is Q06. When the diode failed, it put Q04 into saturation (FULLY turned on), meaning it had only .65V drop across it, which in turn took out everybody connected to it by putting them into an over-voltage condition. A classic example of a Cascading Failure.
So that's where I'm at right now, changing transistors, and getting ready for a brief test when they're all replaced. After I verify all the voltages are back to where they should be, I'll be ready to run it at 50% power for a few hours while I monitor the temperatures to make sure nothing goes bonkers, and then run it Pedal-to-the-Metal for a couple of hours to see how it well it performs.
Gettin'n close, finally, to a resolution on this one.
Been flat on my back since Monday. Aches like I've never had (even my knees hurt), coughing, sneezing, going between sweats and chills, and all sorts of other things.
Finally got out of bed today for more than 30 minutes, and while I'm still a bit wobbly, at least I'm feeling somewhat better.
Was celebrated yesterday. My Sweet Little Wife, knowing me rather well, decided to get married on Valentine's Day so I'd never forget what day it was.
Pretty smart cookie, she is!
Her Maid of Honor and the Minister who married us will be out here in May for a Girl's Trip, so we'll renew our wedding vows while they're here.
I didn't really think I'd get married again, but then she came into my life and completed it.
I love you, honey, and I'd do it again in a femtosecond!
Work continues on the Fisher RS-2010, and I finally sourced all the transistor needed to finish it. The parts should be here this coming week.
Have a pleasant weekend (snowing here and cold), stay in Condition Yellow, and stock up on popcorn. I think the next few months will be 'interesting'.....
With apologies to Wayne Carini.......
One of the things about working on old equipment is that sometimes the parts are hard to find, especially if they were declared obsolete years, or decades, ago.
Now while most passive components like resistors and capacitors are readily available, some of the semiconductors are not. Diodes are easy to find, and even the infamous "Darlington Power Packs" now have discrete versions available, but most of the Small Signal Transistors have been extinct for quite some time.
The issue then becomes finding suitable replacements, of modern manufacture. Most "US" transistors have a "2Nxxx" number on them, like one of my old favorites, the 2N2222.
Japanese transistors use a completely different numbering system, as explained on Wikipedia:
"The Japanese technical standard JIS-C-7102 provides a method of developing part numbers for transistor devices.[1] The part number has up to five fields, for example in the number 2SC82DA:
OK, so that at least tells me about what they are, but to find out exactly what they are, I had to get the datasheets for each (obsolete) part number. The datasheets list all the parameters for the described part number, and from there, you can use the selection guides on the vendor websites (I like Mouser the best) to find currently available parts with matching specifications.
But what if you can't find a datasheet? Remember, these are obsolete parts, and sometimes a datasheet hasn't been scanned and posted somewhere. Well....then you're getting down to hand-to-hand combat. First you look at the schematic, and see what the applied voltages are, and make a best guesstimate as the the current and power dissipation required.
This is the schematic for the right channel of the power amp :
At this point I've found current replacements for all but three of the original transistors, but it's going to take a bit longer to decide what to use for the last three.....
And it might hit Seventy on Monday. And it's been pretty windy, with wind warnings of sustained winds of 50~60MPH, with gusts to 85+ up around the Colorado/Wyoming border.
The dog sure loves it as she can sit outside, pull her ears back, half close her eyes, sit into the wind, and sniff, sniff, sniff about as long as she wants to.
Picture from November:
Had the windows open to air out the house, and even did a bit of yard work, and admired the new fence. Yes, the installers used metal poles, like for a chain-link fence, dug the holes with a little tow-along auger, and set them in with QuickCrete, plumb-lines, and levels. The next day they hung the new panels, and cleaned up the remaining bits and pieces of the old fencing.
Looks nice, but I see I forgot to secure one of my radials to it.
And work continues on the Fisher receiver, with a big post to follow.
Hope you all had a blessed, peaceful Sunday, and stay in Condition Yellow.....
Or should that be Odyssey?
You might be thinking that since this was the "Original Problem" that brought it here I would have tackled it first, and I did do some troubleshooting very early on this assembly.
BUT....(always one of those...) when I noticed the underrated capacitors, the extra parts on this board, the out-of-date "Service" Manual that doesn't match the "As Built" configuration, and the tuning mechanism that fell apart in my hand, et al, I knew I needed to address those issues before I continued on.
So I took care of all the other issues this receiver had before going into the Power Amp.
After carefully bringing it up on my "Variac" while monitoring the current (YAY! NO smoke!), I started checking the voltages on all the transistors. ALL of them were way off, indicating some other issues on the board. A search on the AudioKarma forum showed that this is commonly caused by some of the diodes used to bias the transistors were failing. Sure enough, two of the six diodes used were shorted, and both of the 12V Zener Diodes had failed; One shorted, and the other not regulating at 12 Volts. Unfortunately this took out a couple of small signal transistors on the board, so I have to make another trip down Substitution Lane to find some suitable, currently made transistors.
So the work continues, one step at a time......
And YOWZIR! It's gonna be COLD the next few days. We've had a night here and there that were below zero, but this week should break the record for the season
Started snowing around 1700, and now at 2140, we have a good 3" on the "Snow Table", and it's still kinda-sorta snowing. Looks like dry, fluffy snow, and it's going to stay that way. Should be easy going for the Ariens tomorrow.
Took advantage of the 60* ( ! ) weather the last few days and knocked out some yard work. Got the Big Back Gates secured properly for winter weather, and cut six more logs up and stacked them in the garage. After they finish drying (Reeeeal fast here with the low humidity) I'll split them up for the wood box. I'd really like to find a place where I could get some "logs" about 6~10" in diameter and 6~8' long. I can cut them to 18" lengths for the fireplace, rack 'em in the garage, and split-as-needed, which is what I've been doing with the huge limb that came down from out Ash tree in the back yard. Geez....We've gotten four years worth of firewood from that fall!
Annnnnnd.....Work continues on the Fisher, with another post in the works. That thing has some very poor design and layout issues, other than the low cost capacitors they used.
And it takes some and digging around when the Service Manual is wrong, the parts called out on the schematic don't match the parts in the Parts List, and some other things.
Take care of yourself, take care of each other, and keep that head on a swivel!
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