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Family_Dog

Technics SA-E5 Speaker Terminals

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Hi Guys,

 

Not sure if this is the correct board in which to post, I was looking for a "Vintage" section and this seemed to be the only relevant forum.

 

I have collected quite a bit of Vintage gear over the years, mainly Pioneer, Sansui & Technics. I have repaired/restored may of these items and thought I would post here what I did this lazy balmy day today.

 

Below is simply a 'copy & paste' from our local AVForums South Africa.

 

 

 

So it was time to give the SE-A5 that I bought from KK a while back some loving attention.

 

TechnicsSE-A5NewampOldSpeakerTerminals_z


I had not even yet switched the SE-A5 on yet, but I abhorred those crappy speaker terminals, one of which was broken. Don't worry, I knew about it prior to purchase and one could simply have used the "Remote" terminals, maar nou ja!

TechnicsSE-A5OldSpeakerTerminals_zps3516

 

I figured it would be a reasonably quick job, probably an hour or two at most, but more about that later!


So I set about removing the old terminals and the easiest way to do so was to simply remove the whole Audio board, 4 screws and a couple of plug-in cables. The thicker output cables were hard-wired but no problem to simply swing the board to the best position for working on it.

This pic depicts the old board as well as the new binding posts and an ali-plate that I cut, drilled & punched to suit the new holes, as the old ones were far too large and the spacing was about 2-3mm out.

TechnicsSE-A5NewampOldSpeakerTerminals2_

I toyed with the idea of spraying the ali-plate black but in the end did not bother as it was practically completely out of site anyway.


To connect the PCB to the new binding posts I used some left-over hook-up wire that I have used for all my home-built amps, bought about 40 years ago when copper wire was cheap enough to buy 100m rolls of every colour known to man, and still doing good service. Copper was copper in those days! I decided to fit lugs to fit the binding posts so that the Audio board can be easily removed in future, if necessary, rather than solder directly on to the new binding posts.

But now the first problem arose - the left pair of bonding posts snagged against the plastic cover of the one speaker protection relay, that Technics conveniently put there just to mess me around. So I had to cut both solder tips off the two left binding posts and then also had to saw the one threaded bolt shorter as well.

 

TechnicsSE-A5NewTerminalscatchingonLeftP


Note in the pic above, the Audio board is laying to the left of where it normally rests.

More fun: The little solder tip I cut off jumped into the great abyss of the darkest depths of the amp towards the power supply, which is just a maze of thick wiring looms and I could not find it. So I stripped the rear panel and removed it, unscrewed the fuse block, the voltage selector, the small transformer (or choke ?) hidden under the maze of wires, still could not find the li'l bugger. The pic below shows the inside of the amp, the mass of power supply wires lays beneath the black plastic cover in front of the mains transformer

 

 

TechnicsSE-A5InsideTop_zps9a3a6793.jpg



Gave up on the looking for the tiny little brass doody that was messing me around and started assembling the amp, Every thing fitted perfectly; I was a bit concerned that the base of the ali plate might catch on the top of the PCB but I had left sufficient clearance so no problem there. And then, as I was placing the Audio PCB in its correct place, I found that stupid little brass solder pip that I had cut off stuck on one of the Audio Board heatsinks! Tiny thing, smaller than the head of a matchstick, so no photo but it was relocated to the dustbin.


The rear inner view of the new binding posts:

 

TechnicsSE-A5NewTerminalsRearInnerView_z


Note the top right (well, when working from the back of the amp, it was the left one!) binding post solder tip removed (this was the errant one) and the post below it had to be shortened and only one nut to hold the terminal lug and fasten the post.


And that was that, the job took a while longer than planned because firstly the disappearance, and subsequent reappearance, of that tiny solder pip that committed hari-kari inside the amp cost me about an hour of unnecessary stripping of the amp, and secondly, a Windhoek Laager called my name. Finished the job this morning and switched on, all seems good but have still to connect it to some speakers. The meter lights seem to not be working so that will be the next job.

 

TechnicsSE-A5NewSpeakerTerminals_zpsd9fa


Yes, a keeper!


-F_D
 

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Hmmm.... OK... There is a single solitary push-button switch near the lower centre of the front panel. This sets the output power from the nominal 120w to around 30w, apparently for subdued night-time listening. That switch also controls the meter lights, when in low power, itswitches them off. Crafty! This I found out after testing all the globes (which are series-wired) and finding that they are all A-OK!

 

 

TechnicsSE-A5_1_zps153d7a7f.jpg

 

 

-F_D

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Not a touch on "The Master", pete, but your comment is appreciated. Yopu have done some excellent restorations which I am still reading about.

 

So after final testing last night, the On/Off button simply disappeared behind the front panel when I switched the beast off. Off with the cover, only to find out that the switch itself was fine but the pushbutton in its plastic holder was simply glued to the reat of the front cover and over time this glue had lost the will to live. A bit of a clean-up and a dab of Superglue soon sorted that out.

 

Amongst my pile of odds and ends, I found a Marantz AV600 Tuner/Preamp which I will be using together with the SE-A5. Ideally, I would love to use the partnered Technics pre-Amp but I do not have this - yet.

 

 

-F_D

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*Drools* I would love to own this amp haha!

 

It would make a nice addition to my SU-Z980's pre-out.

 

Great work done to it too!

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OK, here's a bummer! The SE-A5 played absolutely perfectly for a few days and then went into protection. Volume was not set high.

 

Off with the covers and start looking - but where?

 

First thing was to check the setup as per the manual, all was good. Started probing around the voltage regulator circuit as Q311 is prone to pop on these amps and Technics issued a service bulletin in which they suggest a resistor in each channel be changed from 68-ohm to 100-ohm. This had been done by a previous owner.

 

But now here's a thing: Q312 is a 2SA1124 PNP transistor, my Technics had a 2SC640 NPN transistor fitted in its place. I do not have 2SA1124 trannies nor can I find any place in RSA that has them in stock, the closest I found (that I have) is an NTE159 PNP trannie which looked as if it would work albeit with different gain & Ic characteristics.

 

Inserted it, taking care to swap the leads around as the configuration is different and reset the voltages & quiescent bias once more as per the manual.

 

The SE-A5 worked for a couple of hours then went into protection again.

 

There are no dry joints, there is no sign of over-heating and all voltages seem correct. DC bias on the speaker posts does seem to vary slightly but when the set goes into protection, this of course is removed.

 

Before I end up bald (I am already grey), does anyone else have suggestions for me?

 

 

-F_D

Edited by Family_Dog

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Latest:

 

Sadly the amp is lying in pieces on my workbench :(

 

post-150010-0-30696100-1421517721_thumb.


It played absolutely perfectly for about a week, then kept cutting out and going into protection. Traced various faults, one of which amazed me somewhat, somebody had fitted a NPN transistor (2SC640) in place of a high-voltage PNP one (2SA1124) in the power regulator circuit. But it still worked, strangely enough. Not having a 2SA1124 transistor I used the closest thing I had, a NTE159. Same problem, the amp stayed on for a while and then randomly went into protection mode.

 

 

post-150010-0-88773700-1421518097_thumb.

Q312 was fitted, different lead lay-out hence heat shrink on legs to prevent short-circuits.

Tracing the speaker-protection circuitry - and here I was very ably assisted by my partner at work, who is an electronics fundi (I grew up on valves, not pieces of sand) - we came to the conclusion that the speaker protection relay driver TA7137P IC had an internal fault where the final stage had an intermittent open-collector status and its output was going high intermittently, thus enabling the speaker-protection relay. Proof of the pudding was the fact that there was nothing triggering it to do so as those voltages were spot-on. By earthing the IC's output, I could bring it out of protection. But now I had no speaker protection!

 

post-150010-0-26357200-1421518168_thumb.

The IC (Q551) is obscured under the two blue & one orange wires bottom left of the pic (of course, whoever said it would be easy!)
 

 

Frantic e-bay searching web-searching eventually led me to a local supplier who had just one IC in stock, as well as 2SA1124 trannies, so I am hopeful that by this time next week, the Technics will be its usual chirpy self again!


-F_D

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Sadly the amp is lying in pieces on my workbench :(

 

 

 

But not any longer! It is singing happily along (and has been for the past seven hours) since I replaced that gaga TA7137P speaker-protection IC. While I was at it, I replaced the temporary NTE159 transistor with the correct 2SA1124 which I also managed to get locally. The biasing was still perfect, so I guess I could just as well have left the NTE159 in, but I've got them now.

 

 

post-150010-0-43841400-1422121745_thumb.

 

 

The sexy power-amp is definitely a KEEPER!!

 

 

-F_D

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Yet again the Technics went into protection mode, and so back to the work bench once more. This is getting tiresome but i suppose with vintage equipment, this sort of thing can be expected. I was becoming somewhat disillusioned with the SE-A5 because nothing made sense, whenever I tested it on the bench, everything just seemed right. Put it back into working mode and a few days - weeks - later, the ugly "Protection Mode" lamp shone brightly.

SO - back to the work bench but this time a little gut feeling hinted to me to hook up the 'scope to the speaker protection IC 'trigger' pins, so I did just that. Lo & behold, all was revealed - there was a very noisy 50Hz half-wave floating on Pin 1 of the IC, which is the pin used to measure for DC on the Speaker terminals. Now this varied in voltage and when it hit positive peaks, it was just enough to trigger the IC into protection. This "AC ripple" is not evident when measuring DC with a DMM, which is what I had been doing up to then. The diode is used to provide a negative bias of -0.9v to pin 1 of the IC, any voltage approaching 0v and above will trigger the IC into protection.

Unfortunately I never took any photos of this because at that stage I figured it would not prove anything.

Now, high ripple in a rectified circuit is usually due to a reservoir cap being duff, so out with the 50uF 3.3v cap and in with a new 50uF 50v (all that I had, but same physical size) and I felt confident my troubles were over.

They weren't, a few minutes later the amplifier went into protection once more.

Disgusted, I left it for a couple of weeks partly because of the damn 'flu I picked up and also because I just didn't feel like taxing an already worn-out brain.

The 'flu passed and I wondered - not for the first time - whether the little rectifying diode wasn't faulty. But I figured it is such a low voltage (12v AC) and so lightly taxed with only milliamps flowing through it, that it could not possibly be faulty. A diode normally works or it does not, I have never come across one that works intermittently.

Until now! I replaced the diode with a 1N4007 (again, all I had) and switched the amp on again, expecting the protection lamp to once more burn brightly. Well... this was yesterday lunch time and up to now, Sunday afternoon, the amp has not yet gone back into protection. A quick couple of checks with the 'scope showed a near perfect DC waveform without AC ripple.

The guilty parties here are D551 and C552 in the circuit below.
 

 

post-150010-0-35344900-1427647456_thumb.


Now the number of times I thought about putting a 'scope probe to the pins of the IC and then pooh-poohed the idea as insane, the number of times I bumped the amp against the 'scope base as I turned the amp over (the 'scope is mounted on a smaller shelf above the work bench in the previous pics), and the number of times I had to move the scope probe leads which kept getting in my way as well, were all trying to tell me something: Use the Oscilloscope!!

Touch wood, it seems that the cause of the intermittent tripping of the SE-A5 was one ridiculous 5c diode! Changing the electrolytic cap is also a good idea because the original cap would obviously have had AC applied across it during the times when the diode went leaky.

This is the type of repair that should only have cost less than 50c for components and 30 minutes labour - had one known! I tried to eliminate all the usual suspects and could never find a specific fault, although when I replaced the original TA7317P with newly-purchased ones, all the readings went completely haywire. It seems that those ICs were incorrectly marked and were actually other ICs but definitely not the same as original TA7317P types.

 

post-150010-0-81207900-1427647556_thumb.

So far so good, the Technics is happily singing once again coupled to the Marantz tuner/pre-amp combo and Wharfedales and is once more making very sweet music!

 

Please hold thumbs that I do not have to add yet another sequel to this, but so far, so good!  :)


-F_D


 

Edited by Family_Dog

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One week later and the SE-A5 (in daily use) is still merrily chugging along!  :)

 

 

-F_D

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It is now one month to the day, and all's well still!  Happiness :)

 

I kept the diode that broke down "under stress", it still tests fine with a DMM out of circuit and I am still befuddled as to how it broke down under such low voltage and current demands.

 

 

-F_D

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All things fail.

It's called entropy.

 

As for your diode, maybe oxidation that started from manufacture ?

Vibration fracture ?

Diodes are known to be 'noisy' components at the best of times.

 

Last few repairs I've had have been stupid small things that had no right to fail, yet they did.

A single 1/8th watt resistor (in a chain of two) went o/c and tripped an amps power supply into full rail swing to one side that thankfully put it into protection. Cause 55vdc into a speaker isn't good for it :D

Another integrated amp that intermittently wouldn't select the right input (or any at all) because a single transistor was generating noise at its output feeding an input i.c.

 

Times like these you just want to replace everything so you don't have to worry about pulling it all apart again.

Except for the realization that some parts do fail from new............

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Nothing beats the good feeling of having luck on your side and gazing upon serviced equipment still chugging along for many hours of listening to come. 

 

I had something happen years back with an EL84 amp that kept blowing tubes and arcing them. Could not source any problem till I started eliminating one component at a time - very time and cost consuming and ay presto, the result was a weak diode and filter cap, both measured and worked fine in another circuit. So sometimes it is an odd duck.

Edited by DefQon

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And the Technics SE-A5 did it yet again! Protection light came on - speakers dead. But once again intermittently.

Got a bit disgusted at this stage, so simply yanked the SE-A5 out of service and listened to LM Radio using a Denon 3805 powering the MA Silver 6 speakers for the past week or so.

Today being a holiday, I figured let's give it a go. First thing to do (of course!) was to measure and scope the ripple on D551, which powers pin 1 of the speaker protection relay to a negative voltage. Once again, the diode checked out fine and appeared to be doing its job, but pin 1 had a small positive reading of just about 500mv, enough top trigger the IC into protection. It should have read 0.9v negative. But once more, no fault found anywhere else in the amp, so I removed the diode, 1N4007, that I had previously inserted. Tested the diode again - it was 100%.

So now attention turns to the original diode - a Panasonic MA162A, the original of which is - of course - obsolete. But looking at the specs on a 1N4148 switching diode, the two appear to be a good match. I have 1N4148 diodes in stock, so inserted one.

That was three hours ago and the Technics is still a-singing! Now, what can a simple 1N4148 do that a far beefier 1N4007 cannot do, all it does is rectify a very low 11.8v AC at 50Hz, at a current minute enough to probably not even be measured. Perhaps that was its downfall, it might have been too beefy for the job and was incapable of performing at probably a few microamps? Don't know, but let's hold thumbs now for the 1N4148.

As nice as the Denon is, I feel the SE-A5 matches the Monitor Audio speakers better! I was starting to miss that bright and breezy sound.

And so ends another chapter in the saga, let's see for how long ;)


-F_D

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 Now, what can a simple 1N4148 do that a far beefier 1N4007 cannot do

 

 

 

Switching speed.

 

The 4148 will switch a damn sight faster than the 4007.

 

I worked on a HP bench multi meter once.

Some 'tech' was supposed to only align it, but they dropped a probe into it and blew its power supply.

They replaced the 4148's with 4001's.

After several years it came to me totally dead.

 

My research said the diode difference was speed.

 

Swapping out the 4001 for the correct 4148 got the meter trying to work, but the damage this idiot had done was terminal.

The hp custom voltage regs and other ic's were no longer available.

Take one x thousand dollar multi meter and throw it out.

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I considered switching speed, as that is where the 1N4148 excels over the 1N4007. But I reasoned that this was probably not the cause because the unit performed perfectly every day for a period of minimum 6 hours per day and 12-14 hours over weekends. Prior to inserting the 1N4148, I did fit another 1N4007 more out of morbid curiousity and it worked as well for a few hours but then I decided to read up the specs on the MA126A and found it was more or less equivalent to a 1N4148 - indeed a closer match to that than to a 1N4007. So I fitted the 1N4148 and can only assume it is 'cleaner' in operation at this low volatge and current than a 1N4007, which is obviously designed for far higher voltages up to 1A.

 

While replacing the diode, it also gave me a chance to clean up flux residue from previous repair attempts when I replaced the 9-pin SIL Audio Protection IC - four times! I never had anything on hand to clean the flux at the time but Wurth Brake Cleaner does this nicely.

 

 

-F_D

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OK, the Technics is still playing and all still seems good!  :)

 

I have added a 10k resistor across C552 in the circuit above, so that there is a small current drain through the diode. Perhaps it became a bit shaky after the initial charging current of the cap passed through it and I'm surmising it would appreciate a small, but steady, current flow through it to keep it 'switched on'.

 

Time will tell, at the moment it is once more producing that lovely sound that I have grown to love!

 

 

-F_D

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So now with the Technics out of the way, I figured I would pay some attention to one of my Sansui AU-III amps that was slightly under the weather.

 

A fellow AVForums member, Reef, came to visit today, and I conned him into lifting the uber-heavy Sansui AU-111 from the lounge and carry it to the workshop for a once-over. This Amp was connected to the equally heavy 15" Tanny Monitor Gold speakers and should have produced gloriously blazing pure valve sound at about 40w - only it sounded more like 2w at full volume - both channels. This puzzled me because I had not had any volume problems with it before and the fact that both channels were affected seemed to indicate a power supply problem.

 

 

SansuiAU-111_zps4687ac2e.jpg

 

I opened the Sansui up and gawked at about 8 years of dust build-up. Connected the amp to my trusty 30w Sony satellite testing speakers and confirmed the volume was very low on all inputs. Inverting the AU-111 into an upside down position so I could measure HT and bias settings on the output valves - all was correct to within 2%, allowing for possible 240v AC mains variances from the mean.

At this point despair sets in. Was I doomed to rebuild this amplifier ala Johan Potgieter style? I was not looking forward to that and immediately wondered how busy Johan was. I ambled back to the PC & printer so I could print out a copy of the schematic for further digging - always useful when you are probing around 500v DC.

But all voltages checked normal, the valves were still 100% as tested on the AVO Mk 4, all the front panel controls were in excellent health and not sticky.

And that was about the time that I looked more closely to the hum-bucking pot on the rear of the channel which was mounted on the rear panel just out of site in the pic, above the 4 x KT88 output valves. This is commonly used to balance out any potential hum caused by small imbalances in the 6.3v AC heater wiring and I was somewhat astounded that they could use such a tiny dual-ganged pot instead of a beefier wire-wound pot for this. So I carefully adjusted this pot and.................. the audio level increased by some few hundred percent. Sansui had fitted an over-all sub-level audio control and if I had only had the rear of the unit facing me and not the front panel, I guess I would have noticed the pertinent wording that Sansui had so thoughtfully provided for people who lack suitable intelligence - "Sub Volume Level Adjust".

Anyway, all was not lost. I reset this to 90% and grabbed a cell-phone pic of the innards. Please do not compare this to Johan's restoration of the AU-111, but it still looks sexy!

 

My vintage AU-111:
20150620_165316-1_zpsictdecln.jpg

 

 

 

A Sansui AU-III lovingly restored by Johan Potgieter:

post-150010-0-75904300-1434829673_thumb.

 

The "Sub Volume Level Adjust" is easily visible in this second pic, behind the one KT88 closest to the speaker terminals. So easy when you know about it!  :)

Reef, you may come visit me again -  I need to cart the monster back to the lounge.


-F_D

Edited by Family_Dog

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So the SE-A5 started misbehaving again - playing perfectly when set to the low-power position, but cutting out and going into protection when switched to high-power. In order to preserve the meter lights (expensive and snotty to replace), I normally run it in the 30w low-power mode which switches the lights off when running. The other day I wanted to show off the luvverly illuminated VU meters to someone and switched to high-power mode, and the lights came on displaying the true beauty of this magnificent beast. Five seconds later the amp went into protection mode. Back to low-power mode, runs perfectly. High-power mode - protection.

 

Opened it up and took bias measurements - all was fine. Unsoldered the 10k resistor which I had fitted to the input of the protection IC and the amp worked perfectly, all measurements were still in line. Left it on for four hours or so and took measurements again. Immediately noticeable was the left channel heatsink which was running hot, not too hot to touch, but much warmer than the right channel. Measured the voltage of the Bias settings control pot that controls the quiescent collector current of the output transistors and it was running very high at 65mV (should have been 15mV), resulting in the over-heating. So it had drifted. Resetting this to 12mV seems to have cured the problem. Not sure why it ran away like that, I guess one of the biasing trannies might be going wonky but it played fine at the high-power setting for something like 30 hours without going into protection mode again.

 

This is a magnificent amplifier but most certainly not the easiest one to work on.

 

-F_D

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The Technics has been playing for about a week now, so far so good! I did find that it takes a good 30 minutes or so for the collector currents to stabilise, apparently quite normal for this amp and it is running cool with no problems (yet!).

 

Technics_SE-_A5_with_B_O_2600_Speakers_R

 

The Beovox 2600 speakers are probably around 50 years old and still original, including the crossovers. They are probably only rated at 20w or so - if! I have various B&O speakers at hand and just grabbed these because I had already fitted wire pigtails on them, the others I have all require the 2p DIN plug connectors. I am also keen to test the SE-A5 with the Beovox S45 speakers I bought second-hand a few years ago but I need to make up a DIN lead for them first. I have a pair of KEF Concertos which I am also keen to try with the SE-A5 but as can be seen, space is at a premium.

 

The B&O speakers would probably be better off standing on a pair of stands but the pointy ones I have will not do the woodwork any good at all. Think both these options will make a nice combo.

 

 

-F_D

 

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