Technics SU-8077 Rebuild

Well, I am certainly not the expert on this thread. I am the learner. But, did you happen to change the settings on the FL meter trimmers? Did you try re-adjusting them as per the manual?
 
The FL meter trimmers have no influence on the brightness of the FL meters.

There are a couple of options when something is not ok here;

- an issue with the power lamp. This should be the original normal incandescant lamp, 7,5 Volt, 75 mA (or something more or less similar)
- an issue in the power supply
- an issue with the wiring
- an issue with the bright/dim switch
- the meter itself at the end of its life. These meters - unfortunately - wear. Never use them in the bright modus for prolonged time and switch off the amp when not in use
- if you live in "a Manitoba town" it might be bugs

(the latter of course is a joke....)

I would check all voltages according to the schematic to see if there are any irregularities and if it gets everywhere. Take note that part of the voltages is AC!
 
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I was away a couple of days visiting my mother. :) Back now.

Today, I took out and cleaned the four switches that are located on the boards. I cannot mount them back in yet, as I am waiting on the Robbe's Miracle Grease coming from England. Might be a few days yet on that. I will get to the other 7 switches at the front plate probably tomorrow.

I found putting the switches in a small plastic container and doing an alcohol rinse first helped. It kept all the little pieces together, and the alcohol helped take the old grease away. Then I could do the more thorough scrub of the rails with chrome polish and keep the parts contained.

View attachment 893297

I found the first two switches that I did to be actually not bad at all. They looked to me like one had already been done, and maybe one had been replaced. So, I was figuring it would be a breeze and then I encountered the third and fourth switches. They required more scrubbing on the rails. Sigh... But, I think the alcohol helped melt the old dried grease.

While I have this amp apart, can I replace the speaker cable connectors to something that is more modern, like spade connectors? Might be kind of tough, though, trying to find something to fit onto the board in the same way. Do you know if anyone has done this before?

I never change the speaker cable connectors (unless beyond repair), keeping it original maintains the value of the amplifier and the actual binding posts suffice finely when used properly. Some people want to use very thick speaker cable, but I can't find any reason to do so; it will cost you and the quality improvement is zero.

Of course it is your amplifier and if you like it better with other binding posts, then you should absolutely go ahead. You can use anything you want, as long as there is room for it (some people cut holes in the back for this purpose) and the posts do not get in contact with the back plate electrically.

As for the Robbe stuff; I did some research on it, since it's becoming to get unobtainium, I think it can be replaced with other greases containing teflon/ptfe. I guess most important is that the stuff sticks to metal, drives away water and dust and does not seep out over time.
 
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The FL meter trimmers have no influence on the brightness of the FL meters.

There are a couple of options when something is not ok here;

- an issue with the power lamp. This should be the original normal incandescant lamp, 7,5 Volt, 75 mA (or something more or less similar)
- an issue in the power supply
- an issue with the wiring
- an issue with the bright/dim switch
- the meter itself at the end of its life. These meters - unfortunately - wear. Never use them in the bright modus for prolonged time and switch off the amp when not in use
- if you live in "a Manitoba town" it might be bugs

(the latter of course is a joke....)

I would check all voltages according to the schematic to see if there are any irregularities and if it gets everywhere. Take note that part of the voltages is AC!

Thanks for the tips, I checked the Voltage on 511 and 512 and it is 3,1 V. I do not know, how many Volt needs the FL meter. When I checked all the other things (lamp, wiring ...), I switched the Voltage selector at the rear, back to 220 V and the FL meter became brighter ! The voltage on 511 and 512 was now 3,5 Volt. Can I leave the AC Switch on 220 V ( in the socket I have 239 V) or can i change the R 511 resistor who makes the Voltage for the FL meter?
 
But what voltage do you have at fuse F503? Beware, this is AC! What lamp do you have at 504/505?

220 Volt where you have 240 I would not recommend for the 8077 (and for sure not for the 8088 and 8099), it will stress all your components above design and it will generate more heat.

Here in Holland wall voltages over time have changed from 220 to 230. If an amp has a voltage selector I sometimes choose to keep it on 220, because it will generate a little more power in that way, but not every amp will be able to stand it for prolonged time, 240 instead of 220 even makes it worse.
 
Yesterday I took some time to correct a problem in an SU-8080 that I already had shelved for a while.

When the source selector was at its normal position, there was no sound. Only when it was slightly turned the sound came on.
That indicated something was wrong with the switch.

That indeed was an option, since I rebuilt this amp a couple of years ago, sold it and now recently took it as a partial payment on another amp I sold to the customer.

So, what was wrong here? This amp contains three switches with a similar pinout, but two have three turns and one has four turns.
The four turns one was the one with the problem.

I took it out, took it apart and recleaned it, mounted it back and hey....
nothing.
What the...

I then thought that perhaps I mounted the slider wrongly, so I repeated the whole circus of taking it out, taking it apart etc.
I then found...
nothing
The slider could just be in one position only.
What the...

Ok, time for a more agressive strategy.
I took another SU-8080 (you'd need one to do that!), took out the switch, took it apart and...
compared it to the other switch.
Finally I found...
nothing.
Grrrrrrrrrrrrrrr.

Until......
the devil is in the detail
I found it...

aMrGlHX.jpg


eX4r08E.jpg



Obvious, huh.
 
Heh, I see. The clamp jumpers in the bottom picture actually do establish connections to more pins than in the top one.

Reminds me of my SU-A4: here's one of its switches disassembled:


Have a look at the blurry background. Notice something? It apparently came assembled like this from the factory! Luckily there's no difference in operation, despite this little glitch.
 
But what voltage do you have at fuse F503? Beware, this is AC! What lamp do you have at 504/505?

220 Volt where you have 240 I would not recommend for the 8077 (and for sure not for the 8088 and 8099), it will stress all your components above design and it will generate more heat.

Here in Holland wall voltages over time have changed from 220 to 230. If an amp has a voltage selector I sometimes choose to keep it on 220, because it will generate a little more power in that way, but not every amp will be able to stand it for prolonged time, 240 instead of 220 even makes it worse.

On the fuse F503 i have 6,5 V, then is there a resistor R511 (33 ohm) and behind the resistor i have 3.1 V.
The lamp on 504/505 is 7,5 V, 80mA, but there is no difference when the lamp is conected or not.
 
A couple of years ago, I restored and serviced the bigger SU-8099. A hell of a job with a lot of pitfalls. You may find my thread on that one on this forum. I definately want to stress that it is absolutely necessary to clean the insides of the sliding switches. And please be very careful not to break the leads of the heath sensing diodes, which are clamped on top of the power transistors. They are made of unobtainium. Though it might be possible to construct a replacement composed of several diodes packed together; that is a road you want to avoid. Good luck.
 
Heh, I see. The clamp jumpers in the bottom picture actually do establish connections to more pins than in the top one.

Reminds me of my SU-A4: here's one of its switches disassembled:


Have a look at the blurry background. Notice something? It apparently came assembled like this from the factory! Luckily there's no difference in operation, despite this little glitch.

Dreckiger Schalter... :D

Three pin jumpers in that switch? Weird!
 
On the fuse F503 i have 6,5 V, then is there a resistor R511 (33 ohm) and behind the resistor i have 3.1 V.
The lamp on 504/505 is 7,5 V, 80mA, but there is no difference when the lamp is conected or not.

It is weird. I'd expect more than this 3.1 V behind the resistor (unless you measure DC). The dim/bright switch is ok?

Otherwise I'd still suspect an FL meter going less good. You could experiment with changing the resistor for one with a lesser value, but it will again strain the meter more.
 
Heh, I see. The clamp jumpers in the bottom picture actually do establish connections to more pins than in the top one.

Very interesting that your jumpers, and even the rails are different than the ones that I posted in my earlier photo. In case you have forgotten and don't want to look back, I have posted another photo here of the rails and jumpers form my SU-8088. Notice again that the rails and jumpers are different from most that you have posted.

20170326_2244431.jpg

I guess different parts of the world, at that time, used different parts according to what was available.
 
BTW Update on the SU-8088. All of the caps are now installed, including the changes I had to make due to 1) my error in ordering, 2) errors in the service manual. I am still just waiting on the Robbe's Magic Grease before I can finish the re-assembly.
 
Good News! The Robbe's Precision Grease arrived today. I am actually quite surprised at how fast it got here from England. I wasn't expecting it for some time yet.

So, I finished putting the switches together. That went well, except for having to re-do the assembly on two switches because I assembled them backwards. (Not on board, but the switches themselves.) Good learning for next time! :)

Since I had the time, I decided to finish the re-assembly of the amp. Re-soldered the switches back in place, and checked the tiny solders on the back with a jewelers loupe. That all went well, too. Put all the boards back in place, and locked them all down with the brackets provided. I double checked and triple-checked that I did not miss anything.

Then, I fired it up using the dim bulb tester. More good news. The bulb went dim, and the new relay switched on in about 2-3 seconds. Excellent. If you remember, the original relay was taking 20-25 seconds to click on. Nothing sparking, nothing smoking, so I went to the next step.

I then plugged it in without the dim bulb tester, and then let it warm up a few minutes. Now to adjust it.

First, I set the constant voltage to 48 volts. With the new trimmers (love them!), I got it to +47.97 volts, and -48.10 volts. If you remember, when I did the original measurements before servicing, it came in at +31.5 volts and -31.25 volts. This is much better.

Then, I set the DC offset to exactly zero on both channels. Excellent. Before they were set to 26mV for left and 79mV for right. I was surprised that I got to exactly zero on both, but I will take it.

Finally, I set the idling current for the power transistors to 15mV for left and 16mV for right. Before service they were 10mV and 9mV respectively.

The final step was to put the amp back in place and try it out. Oh my gosh, what a fantastic sound! I notice that the highs are clearer, but the bass is still as strong as it always was. Very clean, very clear sound, with excellent sound stage. I am very happy. I will keep a close eye (and ear) on it for the first little while, and let you know if I find anything wonky, but so far so good.

Thanks everyone, especially Jeromach, for all the help and encouragement! Now, wine and music...
 
Super, congratulations! Ready for the next 40 years.

Praise for me perhaps, but for sure for you too, since I haven't met someone who was able to - except for some smaller hiccups that I even today experience all the time - manage to do a complete rebuild so meticulously well.

I'm afraid I would be a much less good music student :).

Ok, next time you're in Veendam please bring me a visit, I will do the same first time I'll be in Canada, so I can admire the 8088 in its full glory as well as meet its friendly owner :)
 
Praise for me perhaps, but for sure for you too, since I haven't met someone who was able to - except for some smaller hiccups that I even today experience all the time - manage to do a complete rebuild so meticulously well.

I mentioned before that in doing this work, I recognize that I have the luxury of time. A real repairman (and I am in no illusion that I am a repairman now!) does not have that luxury. Repairman must get it in, get it diagnosed, get it repaired and back out the door in one week max. I have had this amp apart for a few weeks now. If the owner complains, it is my own fault! ;-)

From our musical world, I compare it to this. Drew, whom you met on this site, is a fantastic repairman of musical instruments (winds). I have worked for him, but am under no illusion that I am as good as him. When it comes to diagnosis, that is where the real skills come in. But, he has to deal with literally thousands of instruments that just need a good cleaning, fix a quick problem or two, and then send it back out the door. What he would really like to do is spend his time rebuilding high-end instruments, but few people will pay what it takes to have that done, as well as give up using that horn for the next several weeks while it is being rebuilt.

As an electronics repairman, I would have a great deal of trouble spotting why things are not working. I have also had the luxury of using equipment that is basically working, but needs rebuilding. That is a completely different story than diagnosing and repairs. I might still have to ask you some questions!

Speaking of which, I have purchased an SU-8600 off the internet for cheap. It should arrive here shortly, and then I am going to see what I can do for it. Maybe there is a market for amps here after they are rebuilt. But, this one comes with a flag that it powers up but has "no output." (Hence the reason it was cheap). We shall see what I can do with it once it gets here.

BTW I would love to visit Veendam! I am hoping that my concert band (I am the conductor) will visit there in 1-2 years, as we have a band from nearby there visiting us next month. Very cool! Should be a blast! (pun intended...)
 
Thanks for the kind word, Dad! I'm excited to hear the SU-8088!
I think there is a market for vintage amplifiers that have been re-build/upgraded. Especially with the big vinyl boom right now. I think people will dig the old amps out of the closet and find that they need repairs.

BTW, you're not going to Veendam without me. There are some really great wind instrument repair shops in Holland that I'd like to visit.
 
Cooll guys, would be nice to meet you here. Although, Canada might be closer by for me (just a 20 minutes ride to Schiphol airport), while Veendam is a 2½ hour drive from here... :D

The 8600 is a nice amp, but has its own "set" of problems.

Some tips in advance;

Check for the presence of the pre/main amp jumpers in the back (one of the most common "faults" I have seen with these amps :))
Clean all the switches. You can try deoxit to see if gets to work, but in the end you'd need to take them out and clean them. Best is to do them one by one, so to not mix up internal parts. Ah, and if I recall well, this one has the very tiny metal parts between slider and lever that can easily be lost, be careful.
NEVER EVER adjust the bias voltage without first replacing the trimmer pot meters. Unless you like fried power transistors.
The volume potmeter is a pita. It can't be accessed and it can't be taken apart properly. My solution, drill a tiny hole at the upper left or right sides of the several compartments, then put in some deoxit. Afterwards, close the cap again, either with tape or with a plastic filler cap. I specifically stock these for that purpose.
Of course the relay needs to cleaned or replaced and all electrolytics, since the lilac panasonic ones mostly are bad or just broken. In front of the filter caps is a place where a lot of heat is generated, the caps at that spot will be bad, but mostly also two resistors will have cracked mantles. They probably function normally, but perhaps better can be replaced too.

The picture below shows some of the nasties; the lilac caps below the filter caps, one of the bias trimmer pots at the right side and the resistor with the cracked casing below the two large 82 ohm resistors.

FYUNth0.jpg
 
@jeromach: what about Wageningen? I'll have to move there in summer for the PhD, and I'll definitely bring my system with me! Otherwise, a trip to Amsterdam is of course never a bad thing IMHO.:)

Oh, and edit: if Technics engineers messed up something, it's definitely the trimmer pots. I HATE those things; in my SU-A4 even staring at them in a sincere way makes the phono DC offset voltage turn from +10mV to -500mV. Urgently need to replace them cheesy crappy bastards!
 
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