In Need of SA-7800 Schematic
- Thread starter greap666
- Start date
Quit is a four letter word, and is infrequently used in my vocabulary.
don't mistake time gaps as loss of interest.
my basement needed pumping out tonight....
that hasn't happened in a few years.
My biggest worry is you getting in over your head, mainly because of the potential of additional damage.
perhaps we can converse over the phone for a few sessions, i sense that the information density we need to exchange is slow and clumsy through these posts.
( btw for lurkers, there have been a LOT of emails going back and forth tonight, summing up, Q26, the driver for the positive half of the output circuit (Q4) was removed and there was still way too much base drive voltage at q26. it should be around plus 1.2 volts)
don't mistake time gaps as loss of interest.
my basement needed pumping out tonight....
that hasn't happened in a few years.
My biggest worry is you getting in over your head, mainly because of the potential of additional damage.
perhaps we can converse over the phone for a few sessions, i sense that the information density we need to exchange is slow and clumsy through these posts.
( btw for lurkers, there have been a LOT of emails going back and forth tonight, summing up, Q26, the driver for the positive half of the output circuit (Q4) was removed and there was still way too much base drive voltage at q26. it should be around plus 1.2 volts)
Cosmic Charlie
Well-Known Member
Sorry to hear that your basement flooded, I thought your gutters were doing their job (somewhat). Nothing worse than an unexpected chore to set you back a few hrs. or days. Hope the sun shines on you today. CC
greap666
Active Member
There are more important matters to tend to now with the flooding and all to worry about this. I really don't have a local tech that can do the work for me that's why I'm giving it a go myself in addition to limited budget.
By the way, this unit is really like an experimental piece. I don't have much invested in it I actually purchased it to supply parts for the SA-7800 that I already have in my stack. I figured since I have all of this equipment I wanted to try and learn what makes it tick. So I'm really not that worried about what happens as long as it doesn't involve electrocution but I also don't want you to waste your time either.
You have spent alot of time on this and I appreciate it.
Thanks.
Bill
By the way, this unit is really like an experimental piece. I don't have much invested in it I actually purchased it to supply parts for the SA-7800 that I already have in my stack. I figured since I have all of this equipment I wanted to try and learn what makes it tick. So I'm really not that worried about what happens as long as it doesn't involve electrocution but I also don't want you to waste your time either.
You have spent alot of time on this and I appreciate it.
Thanks.
Bill
Cosmic Charlie said:
Thanks CC, the sun IS shining now............. BUT ...............
Weather is reporting a probable encore tonight. 90 percent probability, so I'm just going to concentrate on battening down the hatches today.
The backyard was FLOODED last night. Coulda taken that boat / fishing gag photo I've wanted.
The backyard hasn't flooded like that since they paved the alley and installed storm drains, including a storm drain IN a neighbors YARD 2 houses down and 6 inches lower. The backyard used to flood regularily, as the runoff from the Church's gutters always ran into my yard.
But the guy (long since gone) in between me and the storm drain installed an improperly drained RAISED sidewalk before the alley went in (out of fibercrete, that &%$# hairy concrete will last forever!!!) that acts like a dam and makes it 6 inches DEEPER than before....
Giving me a water level a FOOT over the storm drain. Every time it floods, it's too dark for pictures to prove to the city that the sidewalk altered the drainage drastically, and was done without a permit.
When the sun came up this morning, most of the water had settled below the level of the grass, but it's like walking on a sponge, and the sidewalk is still flooded (it's a bit lower than the grass).
Strawman said:
Well, I'm just outside of O'Hare (West/northwest), and the worst of the damage is to the south side and south- southeast suburbs. It was just winding up to throw it's punch when it hit me, the worst whiffed on by and landed further south.
Wanna talk a ripoff? I have a Simer Ace in the hole (a5000) backup sump pump, and the float switch has failed. Simer customer service wants over $55 total for a replacement, with 12 bucks going towards shipping.
And my original sump pump packed it in last night, good thing I caught it fast and had a 1/3 hp utility pump that connects to a garden hose....
(it was the sound of sudden silence during some rapid cycling that tipped me off, luckily!!)
I was standing there watching the water rise in the pit, with the 1/2 hp dead. I was waiting to see my backup pump finally do something... :saywhat:
nothing happens!!!! pressing the test button got the pump going, but i had to keep my finger on the button to keep it running. Grabbed an alligator clip and shorted the two contacts for the float connector, and rustled up that utility pump DA#@ quick.
It looks like we had about 4 inches of rain in an hour IIRC.
I'm gonna get pre-emptive tonight, and find/put another utility pump in the low spot that fills and floods my back stairs, and squirt it out downhill into the yard.
greap666
Active Member
I have no problem hanging with Mark Straw but the first priority is stayin' dry but if the man thinks I'm in over my head I gotta believe him and take whatever advice he gives me. Don't want him going crazy over some blown amp it ain't worth it.
Good luck Mark you'll be ok.
Good luck Mark you'll be ok.
Strawman
Addicted Member
Damn Mark, I hope it all works out good for you. I bought into a "flood plain", and had a water driven backup installed just in case the pump went out. Hired an independent surveyor, and got out have to pay the 1K and growing annual insurance. 4K later, and I don't pay it anymore. best of luck, there bud.
Greap, Mark will let you know know when it's time to throw in the towel, no offense inteded, but long distance fixing can reach a point where it isn't safe.
Good to see that you're interested, and I hope you get it alive, you'll know when it's time to "pass the torch".
Greap, Mark will let you know know when it's time to throw in the towel, no offense inteded, but long distance fixing can reach a point where it isn't safe.
Good to see that you're interested, and I hope you get it alive, you'll know when it's time to "pass the torch".
greap666
Active Member
I hear ya Straw I don't need to be leaving any money to anybody sooner than I need to. Believe me I understand the hazards when dealing with electricity. In the past I even had a chance to feel the wrath of 480 volts.......burnzzzz just a little bit.
But the first priority is staying dry and controlling the flood waters.
But the first priority is staying dry and controlling the flood waters.
Greap: take some pictures for yourself, that show the board before you do anything, they're a great reference for the question "now how was that thing in there?"
Then one at a time pull each of those nine transistors (13 actually) and test them, then replace it, IF it tests good. The idea is not to confuse yourself and mix up the transistors.
WRITE STUFF DOWN, paper NEVER forgets ---- I DO IT TOO!!!! -------
make drawings if necessary to be able to return things EXACTLY as they were found, especially lead arrangements.
That's the philosophy (mine too), ALWAYS be able to back out gracefully.
Troubleshooting is a methodical, careful enterprise, accumulating data until something clicks, and that Ah hah moment happens.
If you are fuzzy on the 6 tests needed to check EACH transistor, STUDY the EchoWars post I provided a link to.
If you have a question, ask, there will be plenty of answers.
Just because I'm floating down the river doesn't mean you are stalled.
Then one at a time pull each of those nine transistors (13 actually) and test them, then replace it, IF it tests good. The idea is not to confuse yourself and mix up the transistors.
WRITE STUFF DOWN, paper NEVER forgets ---- I DO IT TOO!!!! -------
make drawings if necessary to be able to return things EXACTLY as they were found, especially lead arrangements.
That's the philosophy (mine too), ALWAYS be able to back out gracefully.
Troubleshooting is a methodical, careful enterprise, accumulating data until something clicks, and that Ah hah moment happens.
If you are fuzzy on the 6 tests needed to check EACH transistor, STUDY the EchoWars post I provided a link to.
If you have a question, ask, there will be plenty of answers.
Just because I'm floating down the river doesn't mean you are stalled.
greap666
Active Member
Thanks Mark I appreciate it. You know me with pictures I have no problem taking them. I'll review the link of which I have bookmarked and pull the 13 and test.
I'll let ya know once I get them tested along with the numbers.
Hang in there buddy I'll throw ya a rope if ya need one.
I'll let ya know once I get them tested along with the numbers.
Hang in there buddy I'll throw ya a rope if ya need one.
greap666
Active Member
Just to insure that I don't waste too much time desoldering and resoldering I just want to insure the following are the ones that need to be pulled and tested:
Q2,4,6,8,10,12,14,16,18,20,22,24,26,28
That's 14 but if I understand you correctly you said 13 since we already pulled Q26.
I'll await your answer before continuing, while I wait I'll do a bit of reading.
Q2,4,6,8,10,12,14,16,18,20,22,24,26,28
That's 14 but if I understand you correctly you said 13 since we already pulled Q26.
I'll await your answer before continuing, while I wait I'll do a bit of reading.
Cosmic Charlie
Well-Known Member
good luck with the weather Mark, I hope it holds off till you get your pumps in order. Greap, keep plugging along, as long as Mark doesn't get frustrated. I'm sure you are learning, gotta start somewhere, What town in Ct. do you live?. I live out by the Indian casinos Foxwoods and Mohegan Sun, just curious. CC
greap666
Active Member
Hey Mark just to keep you abreast. I've just pulled my working SA-7800 from my stack to also use as a cross reference with photos and notes in the event I have questions about the positioning of the pulled transistors. Also after pulling it I performed the same test that we did last night to see what the actual readings should be on two good channels along with just a visual inspection while it's open....but I ain't messin' with a good working one that's for sure!
greap666 said:
YIKES... was I out of it!!
I thought I had generated a list of transistors on this thread, I hadn't....
Q2 is a dual transistor that shares a common emitter lead, so adjust the testing accordingly, Q4 has the base and collector connected, so also adjust accordingly, one side can be tested as a transistor, the other as a diode.
Q6, Q8, Q10, Q12, Q14, Q16, Q18, Q20, Q22, Q24, Q26 on this board, and the power outputs Q2 and Q4 offboard will test normally.
It won't hurt to test Q28, but that isn't part of the amplifier circuit IIRC.
Yes your list IS correct.... and I didn't hit the suds last night..... :screwy:
Use minigrabber clips for readings, and insulate all but the very tips of your probes so any slips of the probe (and that happens to us ALL) isn't a recipie for tears.... :tears: or bad language....
greap666
Active Member
Hi Mark,
Glad to see you're still with us and not down river.
No problem with the list. I figured since that was the bad channel from the previous tests those were the ones.
Can you give me an idea of the possible test results on the DMM lets sau for Q26. I just want to make sure that I'm doing it correctly and not giving you the wrong readings.
Glad to see you're still with us and not down river.
No problem with the list. I figured since that was the bad channel from the previous tests those were the ones.
Can you give me an idea of the possible test results on the DMM lets sau for Q26. I just want to make sure that I'm doing it correctly and not giving you the wrong readings.
OK, here are the results of multimeter diode tests on TWO GOOD bipolar transistors,a 2sa725 pnp transistor and a 2sc945 npn transistor (from a sx-550):
first the PNP:
black lead to base, red lead to collector, result = 675
black lead to base, red lead to emitter, result = 688
red lead to base, black lead to collector, result = OL = No conduction
red lead to base, black lead to emitter, result = OL = No conduction
black lead to emitter, red lead to collector, result = OL = No conduction
red lead to emitter, black lead to collector, result = OL = No conduction
next the NPN:
black lead to base, red lead to collector, result = OL = No conduction
black lead to base, red lead to emitter, result = OL = No conduction
red lead to base, black lead to collector, result = 677
red lead to base, black lead to emitter, result = 680
black lead to emitter, red lead to collector, result = OL = No conduction
red lead to emitter, black lead to collector, result = OL = No conduction
stating it another way:
B..C..E....PNP....NPN WHERE B=BASE, C=COLLECTOR, E=EMITTER, PNP AND NPN ARE RESULTS
B..R...x....675....OL decoded: black lead to base, red lead to collector, emitter not connected, pnp conducts and npn doesn't.
B..x...R....688....OL
R..B...x....OL......677
B..x...B....OL......680
x..B...R....OL......OL
x..R...B....OL......OL
The first row is the header and is the only row where b means base of the transistor. That first row defines which transistor lead we are talking about. On the next six lines B means the black meter lead and R means the red meter lead. x means NO connection. OL means there is no conduction (high resistance) and a number means there is conduction and the voltage drop across that transistor junction.
Just for grins here is the link to EchoWars Bipolar Junction Transistor Testing Basics thread.
first the PNP:
black lead to base, red lead to collector, result = 675
black lead to base, red lead to emitter, result = 688
red lead to base, black lead to collector, result = OL = No conduction
red lead to base, black lead to emitter, result = OL = No conduction
black lead to emitter, red lead to collector, result = OL = No conduction
red lead to emitter, black lead to collector, result = OL = No conduction
next the NPN:
black lead to base, red lead to collector, result = OL = No conduction
black lead to base, red lead to emitter, result = OL = No conduction
red lead to base, black lead to collector, result = 677
red lead to base, black lead to emitter, result = 680
black lead to emitter, red lead to collector, result = OL = No conduction
red lead to emitter, black lead to collector, result = OL = No conduction
stating it another way:
B..C..E....PNP....NPN WHERE B=BASE, C=COLLECTOR, E=EMITTER, PNP AND NPN ARE RESULTS
B..R...x....675....OL decoded: black lead to base, red lead to collector, emitter not connected, pnp conducts and npn doesn't.
B..x...R....688....OL
R..B...x....OL......677
B..x...B....OL......680
x..B...R....OL......OL
x..R...B....OL......OL
The first row is the header and is the only row where b means base of the transistor. That first row defines which transistor lead we are talking about. On the next six lines B means the black meter lead and R means the red meter lead. x means NO connection. OL means there is no conduction (high resistance) and a number means there is conduction and the voltage drop across that transistor junction.
Just for grins here is the link to EchoWars Bipolar Junction Transistor Testing Basics thread.
greap666
Active Member
Well folks just to give everyone that cares to hear an update on the progress here. Mark has definitely gone above and beyond to assist me in bringing this baby back to life.
After testing the power supply ass'y we moved on to the power amp ass'y where we found that we had one bad channel. Several resistors had to be replaced along with a systematic and methodical test of all transistors, diodes and resistors in the bad channel. We found two bad output transistors I believe Q3 and Q5 (on the heatsink) and now need to purchase replacements. I fired the amp up today with a tuner and headphones after moving over the two good output transistors from the good channel. The output to the headphones was a success, of course without one channel but definitely a major step to putting one more fine Pioneer amp back in action.
I just can't say enough about Marks patience with me being the novice that I am, several nights staying with me till 1 or 2 am.
Anyway maybe this is a bit premature but I believe the patient will live.
Also the thread that EW put together on performing the BCE tests on bipolar transistors was a priceless tool to have at the bench.
This thread would have probably been easily filled with another 75 or so notations but Mark and myself thought or adapted after a while email.
Anyway as I told Mark the steak dinner is on me.
Thanks again Mark:thmbsp:
After testing the power supply ass'y we moved on to the power amp ass'y where we found that we had one bad channel. Several resistors had to be replaced along with a systematic and methodical test of all transistors, diodes and resistors in the bad channel. We found two bad output transistors I believe Q3 and Q5 (on the heatsink) and now need to purchase replacements. I fired the amp up today with a tuner and headphones after moving over the two good output transistors from the good channel. The output to the headphones was a success, of course without one channel but definitely a major step to putting one more fine Pioneer amp back in action.
I just can't say enough about Marks patience with me being the novice that I am, several nights staying with me till 1 or 2 am.
Anyway maybe this is a bit premature but I believe the patient will live.
Also the thread that EW put together on performing the BCE tests on bipolar transistors was a priceless tool to have at the bench.
This thread would have probably been easily filled with another 75 or so notations but Mark and myself thought or adapted after a while email.
Anyway as I told Mark the steak dinner is on me.
Thanks again Mark:thmbsp: