Technics SU-Z45 vintage amplifier repair

[goodpsusearch]

Got this for free, previous owner said when he connected speakers on amplifier he heard very loud cracking noises and immediately disconnected it to avoid damaging speakers and he was going to throw it away.


When I opened the case I didn't notice anything visibly burn/bulging.

Then I connected some suicidal speakers and turned on amp. Nothing.

Then played with volume control and heard noises that could be due to dry/dirty potentiometer.

Then connected audio input and retried. Left channel was working but the right channel was dead and when cranking up volume, it would make terrible noises indeed, now I get why previous owner got scared.

I checked every cap and found 1 cap that has gone short circuit (0uF capacitance , 5-15 ohm resistance).

I also found some caps that have started to go high esr.

Caps had date codes of 1982, so I proceeded to preemptively replace most of them including the bad ones, using exclusively good Japanese brands 105c and entry level low esr.

Unfortunately the amp uses the dreaded STK IC Here it is STK2038B (not to be confused with STK2038II , they are totally incompatible!) and the right channel is dead.

Sanyo has stopped producing them since late 90s, so it is nearly impossible to find original ones. I was lucky to find some probably fake Chinese clone. Costed me around 10 euros and when it finally arrived, checked it and found it noticeably lighter than the original broken one

So, I replaced faylty STK with good working one and also cleaned the switches and pots with CRC contact cleaner and the amp is working again!

I attach some pictures that I took during repair, unfortunately I forgot to take an overall photo of the amp before putting back the metal cover.

Here are 2 photos from the internet:
http://nvivo.free.fr/Site/Technics_SU-Z45_files/3_1.jpg
https://www.avsite.gr/forum/proxy.ph...f9819d9d5638a6

I also replaced the 2x 6800uF main caps with 2x 10000uF 50V Nichicon GU 105C

[goodpsusearch]

Here is a pic that tries to include every improvement/repair that I made on this amplifier:

https://www.badcaps.net/forum/attach...1&d=1642275924

Any comment is welcome

[CapLeaker]

I've got the same amp in silver. On mine I have a little trouble with the display kicking in and out randomly. I've been saying for the past 8 years now that I am going to fix it, but since there is so much other toys stacked over the amp, I just left it sitting right there. Its a pretty good sounding and simple amp.
Your first post, second link isn't working for me.
Other than that it would be nice to attach the service manual to this thread, if you have one...

[goodpsusearch]

Originally Posted by goodpsusearch

Here are 2 photos from the internet:
http://nvivo.free.fr/Site/Technics_SU-Z45_files/3_1.jpg
https://www.avsite.gr/forum/proxy.ph...f9819d9d5638a6

Uploading second photo here, since link is not working

Originally Posted by CapLeaker

I've got the same amp in silver. On mine I have a little trouble with the display kicking in and out randomly. I've been saying for the past 8 years now that I am going to fix it, but since there is so much other toys stacked over the amp, I just left it sitting right there. Its a pretty good sounding and simple amp.
Your first post, second link isn't working for me.
Other than that it would be nice to attach the service manual to this thread, if you have one...

If I remember correct it has trim-pots to adjust watts level on left and right channel. Mine, always shows one channel watts lower than the other but I didn't feel like disassembling it again.

Another unresolved issue is that the bass level adjust trimpot is not working even though I tried to thoroughly clean with CRC Contact Cleaner. I just let it in 0 position and don't want to mess more with it.

Ok, also uploading every pdf I have, related to the amp

AN7060 is the preamp IC. The unit has 2 x AN7060, each one on an identical daughter-board.

[momaka]

Looks like Panasonic built this amp for Technics, judging by the many AN-- ICs and (old) Panasonic logo on the big transformer.

I guess be careful if you try to crank this thing up. From what I've heard/read on other sites, counterfeit STK modules do work, but conk-out at much lower power output level likely due to small transistor dies for the final outputs (read: cheaper to manufacture.) Certainly better to pair it with speakers that are "easy" do drive (8-Ohms impedance and DC resistance, smaller diameter like 6.5" or 8", and preferably a light paper cone or polypropylene.)

[CapLeaker]

Mine is original... never has been apart and always used "easy" on the volume, but daily until I got it. Mine has a cold solders on the display. I tap the display, I can make it come on or off... It's been like this for a long time However I should be taking it apart and give it a nice refresh some time. At least that is what I've been telling myself. lol

[goodpsusearch]

Originally Posted by momaka

Looks like Panasonic built this amp for Technics, judging by the many AN-- ICs and (old) Panasonic logo on the big transformer.

I guess be careful if you try to crank this thing up. From what I've heard/read on other sites, counterfeit STK modules do work, but conk-out at much lower power output level likely due to small transistor dies for the final outputs (read: cheaper to manufacture.) Certainly better to pair it with speakers that are "easy" do drive (8-Ohms impedance and DC resistance, smaller diameter like 6.5" or 8", and preferably a light paper cone or polypropylene.)

After assembling it, I kind of stress tested it with those speakers:

https://www.dali-speakers.com/produc...tor/spektor-2/

DALI SPEKTOR 2 SPECS
Product series SPEKTOR
Frequency Range (+/-3 dB) [Hz] 54 - 26,000 Hz
Sensitivity (2,83 V/1 m) [dB] 84.5 dB
Nominal Impedance [ohms] 6 ohms
Maximum SPL [dB] 105 dB
Recommended Amplifier Power [W] 25 - 100 Watt
Crossover Frequency [Hz] 2,600 Hz
Crossover Principle 2-way
High frequency driver, Quantity 1 x 25 mm
High frequency driver, Diaphragm type Soft Textile Dome
Low frequency driver, Quantity 1 x 5,25"
Low frequency driver, Diaphragm type Wood Fibre Cone
Enclosure type Bass Reflex
Bass Reflex Tuning Frequency [Hz] 51.5 Hz
Connection Input Single Wire
Recommended Placement Shelf or stand
On-Wall
Recommended Distance From Wall [cm] 1 - 80 cm
Dimensions (HxWxD) [mm] 292 x 170 x 238 mm
Accessories Included Rubber Feet
Manual
Wall Bracket
Weight [kg] 4.2 kg

So, the sensitivity is just 84.5 dB and they are 6ohms speakers. I cranked the volume as high as I could stand but the system was in my bedroom that is too small, so I guess it is easier to fill with sound.

Took a pic while testing:

https://www.badcaps.net/forum/attach...1&d=1643660536

The case of the amplifier just got warm during this. Maybe the 10000uF caps helped the unit, same with MX4 applied as thermal paste. Don't know, but it sounded good!

Technics always belonged to Matsushita ,now called Panasonic.

[momaka]

Originally Posted by goodpsusearch

After assembling it, I kind of stress tested it with those speakers:

https://www.dali-speakers.com/produc...tor/spektor-2/

So, the sensitivity is just 84.5 dB and they are 6ohms speakers. I cranked the volume as high as I could stand but the system was in my bedroom that is too small, so I guess it is easier to fill with sound.

Neat little speakers!

Yeah, despite the low sensitivity, I'm sure they were plenty loud. After all, you have them very near the corners of the bedroom, so that probably helps a lot, especially with the bass output.

They might be 6 Ohms, but the fact that they have lower efficiency and smaller cone size actually makes them "easier" to drive for the amp. Smaller and lighter cones mean less mass to accelerate and stop, which means lower transient currents for the amp. And low efficiency generally goes hand-in-hand (though not always) with lower back-EMF generation... which again means lower transient currents from the amp trying to dampen cone movement (though the low efficiency does go both ways, in that the amp also needs to provide more power to drive the speakers to the same volume as more efficient ones.) But in general, this will usually make the speakers more consistent (linear) in terms of power input.

Originally Posted by goodpsusearch

Took a pic while testing:

https://www.badcaps.net/forum/attach...1&d=1643660536

The case of the amplifier just got warm during this. Maybe the 10000uF caps helped the unit, same with MX4 applied as thermal paste. Don't know, but it sounded good!

Cool setup!

I see you have lots of CDs and blank optical media. The cassettes, though - awesome! I've kept all of mine as well. I even managed to save a few reel-to-reels from my dad. He had a R2R Sony deck, but randomly decided to give it away one day some 20 years back. Luckily, he forgot where all of the reels were. So when I found them 5 years later during a cleanout of my parent's old apartment, I saved all of them. I'd love to get a R2R deck one day. But the prices of those currently... yeah, it ain't gonna happen anytime soon.

[goodpsusearch]

Originally Posted by momaka

Neat little speakers!

Yeah, despite the low sensitivity, I'm sure they were plenty loud. After all, you have them very near the corners of the bedroom, so that probably helps a lot, especially with the bass output.

They might be 6 Ohms, but the fact that they have lower efficiency and smaller cone size actually makes them "easier" to drive for the amp. Smaller and lighter cones mean less mass to accelerate and stop, which means lower transient currents for the amp. And low efficiency generally goes hand-in-hand (though not always) with lower back-EMF generation... which again means lower transient currents from the amp trying to dampen cone movement (though the low efficiency does go both ways, in that the amp also needs to provide more power to drive the speakers to the same volume as more efficient ones.) But in general, this will usually make the speakers more consistent (linear) in terms of power input.

I already knew some of the above information but it's the first time someone put it all together and explained in a simple (but not simplistic) way how they are all connected. Thank you so much!

Originally Posted by momaka

Neat little speakers!


Cool setup!

I see you have lots of CDs and blank optical media. The cassettes, though - awesome! I've kept all of mine as well. I even managed to save a few reel-to-reels from my dad. He had a R2R Sony deck, but randomly decided to give it away one day some 20 years back. Luckily, he forgot where all of the reels were. So when I found them 5 years later during a cleanout of my parent's old apartment, I saved all of them. I'd love to get a R2R deck one day. But the prices of those currently... yeah, it ain't gonna happen anytime soon.

This is an ongoing project.

Me dream is to have a system that will have the following (working :p) parts:

front speakers
rear speakers
sub-woofer

5.1 amp
stereo amp

cassette deck of acceptable quality (doesn't need to be very high end)
turntable
VHS
media player PC with good quality sound card, should be at least ALC1220

Optional:
CD player deck (only if I get for free, wont pay for that)
separate FM tuner (same as above)
graphics equalizer (just to watch the lights synchronizing with the sound level)
DVD Player/recorder (don't really want that, I just have so many lying here!)

I started collecting parts to build that system on my living room. But turns out that due to terrible sound insulation and not patient neighbors I end to listen 95% of my music and watching films on my bedroom. So I started building a second system for my bedroom.

It feels so nice that almost every part is used/repaired and many of them saved from the landfill. I tried as far as I can to avoid buying new crap that will break after some years.

I am going to create new threads and ask for your help as I make progress on this.



BTW I have a Grundig reel to reel that my grandfather found and collected from the dump back in 90s. It has been sitting in storage since then waiting for repair. It is one of the compact, portable ones though. My grandfather passed away back in 2012.

I hope someday I will find the time to try to fix that one too.

I would send it to you without a second thought if you lived in Greece or close to Greece anyway to make it a viable option

[momaka]

Originally Posted by goodpsusearch

Me dream is to have a system that will have the following (working :p) parts:

front speakers
rear speakers
sub-woofer

5.1 amp
stereo amp

In all honestly, I don't think I can say I've ever been impressed by home 5.1 setups, ever. In theater rooms - sure. But at home, it's just really hard to do it properly. First, you have to have a fairly "proper" room for it with good symmetry (for better acoustics.) Then comes the burden of playing with the speaker placement, since that is probably the most important thing of how the system will sound. However, trying to "balance" the sound out of 5 speakers instead of just 2 really really increases the complexity. And even then, you will likely find that no matter how much you play with the speaker placement, there will still be areas in the room with poor acoustics. This goes for a simple stereo setup too, but at least it's easier to correct it overall, since you just have to deal with only 2 speakers.

So IDK, I tend to shy away from those 5.1 / 7.1 setups. More speakers doesn't necessarily mean better sound. It can... but there's a reason why cinemas have professional audio engineers setup their surround sound systems.

Not saying you shouldn't try it, though - that can still be fun, and going through the whole process, you may even learn a lot of new things. Just making sure you don't set your expectations too high and then end up not liking it. You may get really good results... but you may not, either.

Originally Posted by goodpsusearch

cassette deck of acceptable quality (doesn't need to be very high end)

For cassette decks, probably better to go with something from the 80's and that only has one deck. The dual decks, IMO, is where they started making them cheaper and not as good. Of course, good dual decks do exist out there... just fewer. Only problem with getting a really old deck is you'll probably run in the same issues with any old gear - likely deteriorating pots and switches in need of deoxit... AND BELTS!

Originally Posted by goodpsusearch

CD player deck (only if I get for free, wont pay for that)
separate FM tuner (same as above)

LOL! I'm with you on that one, though.

Originally Posted by goodpsusearch

I started collecting parts to build that system on my living room. But turns out that due to terrible sound insulation and not patient neighbors I end to listen 95% of my music and watching films on my bedroom. So I started building a second system for my bedroom.

Originally Posted by goodpsusearch

It feels so nice that almost every part is used/repaired and many of them saved from the landfill.

Same here.
The only thing I buy new (sometimes!) are parts to fix/refurbish old, well-made stuff.

Originally Posted by goodpsusearch

BTW I have a Grundig reel to reel that my grandfather found and collected from the dump back in 90s. It has been sitting in storage since then waiting for repair. It is one of the compact, portable ones though. My grandfather passed away back in 2012.

I hope someday I will find the time to try to fix that one too.

Sorry to hear that. Hope you do indeed get it fixed one day. Would be just another nice thing to remember your grandfather with.

[goodpsusearch]

Originally Posted by momaka

In all honestly, I don't think I can say I've ever been impressed by home 5.1 setups, ever. In theater rooms - sure. But at home, it's just really hard to do it properly. First, you have to have a fairly "proper" room for it with good symmetry (for better acoustics.) Then comes the burden of playing with the speaker placement, since that is probably the most important thing of how the system will sound. However, trying to "balance" the sound out of 5 speakers instead of just 2 really really increases the complexity. And even then, you will likely find that no matter how much you play with the speaker placement, there will still be areas in the room with poor acoustics. This goes for a simple stereo setup too, but at least it's easier to correct it overall, since you just have to deal with only 2 speakers.

So IDK, I tend to shy away from those 5.1 / 7.1 setups. More speakers doesn't necessarily mean better sound. It can... but there's a reason why cinemas have professional audio engineers setup their surround sound systems.

Not saying you shouldn't try it, though - that can still be fun, and going through the whole process, you may even learn a lot of new things. Just making sure you don't set your expectations too high and then end up not liking it. You may get really good results... but you may not, either.

Totally agree with you on this.

It is next to impossible to balance volume levels, early reflections, height of each speaker, etc.

I think that the modern Audio Video Receivers solve many of those issues with the automatic calibration software with the use of microphone, such as audyssey multeq-x and Yamaha ypao.

I am "lucky" that my room doesn't allow a center speaker so I have to deal with only 4 speakers and a sub.

Here is another pic of my bedroom:
https://www.badcaps.net/forum/attach...1&d=1646516894

You can see the ghetto stand of the rear left speaker, the speaker is a cute little Dali Spektor 1, they are perfectly capable as surround speakers.

I watched this horror movie recently https://www.imdb.com/title/tt5140878/
with the now repaired Roister sub and I could hear the sound of pieces smashing from the evil spirit coming from back left.

I don't care about perfection, it's just fan to watch movies like this, especially action scenes like helicopter scenes or bullet scenes. I want to have the same setup on my living room too but I need to fix the other Sony AVR that I have first.

Originally Posted by momaka

For cassette decks, probably better to go with something from the 80's and that only has one deck. The dual decks, IMO, is where they started making them cheaper and not as good. Of course, good dual decks do exist out there... just fewer. Only problem with getting a really old deck is you'll probably run in the same issues with any old gear - likely deteriorating pots and switches in need of deoxit... AND BELTS!

I am now a happy owner of 3 cassette decks:

1)very old rack type single deck, totally dead. Got it for free, will start a thread some day for troubleshooting
edit: found pic of it online:
https://i.ebayimg.com/d/w1600/pict/1...Deck-Mc-11.jpg
but my unit is of black color

2) Marantz SD4050 dual cassette deck, from late 90s. I am quite sure this was not made from Marantz, must be an OEM product that they just slap the name such as Marantz, Pyle, Ion, Pioneer, Teac etc. Seems to be working, might need new belts. Of course the cassette mechanisms are plastic. Supports Dolby B and C. Costed 30 euros

3) Just one week ago, I got a Fisher CR-W345 dual cassette deck along with Fisher MT-345 linear type turntable. Paid 10 euros for both, so I couldn't resist buying them. They were made in the 80s and they were typical Fisher products, made in Japan but relatively cheap. The linear tracking mechanism of the Turntable needs service and the cassette deck needs new belts because the original ones have perished. Will create threads about them too when I find time.

Originally Posted by momaka

Sorry to hear that. Hope you do indeed get it fixed one day. Would be just another nice thing to remember your grandfather with.

Me too

[momaka]

Originally Posted by goodpsusearch

I am "lucky" that my room doesn't allow a center speaker so I have to deal with only 4 speakers and a sub.

You also have to deal with cats, I see.
But I approve! ... and looks like they do as well.

Originally Posted by goodpsusearch

Here is another pic of my bedroom:
https://www.badcaps.net/forum/attach...1&d=1646516894

You can see the ghetto stand of the rear left speaker, the speaker is a cute little Dali Spektor 1, they are perfectly capable as surround speakers.

Nice, I like that setup.
Your bedroom actually looks fairly trivial for a speaker setup, due to its shape and where your listening position tends to be.

In my bedroom / computer room, my listening position (when on my computers) is right in the middle between the speakers on the front and where the back wall is. So I get nice balanced reflections and the stereo image is as good as it can get from a stereo setup. However, the bass is really weak in that position, likely due to canceling waves. I've even tried adding a subwoofer at various positions, but it helps very little. Plus, the few positions where it did, I'd have to trip over it, lol. Also, at that point, the bass in other places in the rest of the room get obnoxiously loud and the decorative PCBs I have on my walls start to make noise from vibration. Pretty sure the neighbor can hear that. So unfortunately I have to make due with reduced bass output. But if I sit back in my bed, which is close to the wall opposite of the speakers, the bass is great.

But again, yours just being a smaller and more symmetrical room, I think you'll always get great acoustics. And I don't even want to imagine what will happen if your turn all the way up that Roister sub in there with the door closed. Well, actually I can imagine what will happen - the door probably won't stay closed for long!

Originally Posted by goodpsusearch

I watched this horror movie recently https://www.imdb.com/title/tt5140878/
with the now repaired Roister sub and I could hear the sound of pieces smashing from the evil spirit coming from back left.

I don't care about perfection, it's just fan to watch movies like this, especially action scenes like helicopter scenes or bullet scenes.

Oh I hear ya.
I did the same downstairs in the living room - moved the table in front of the couches and put a single armchair just a few feet away from the TV, where it's equal distance from all of the surround speakers. Then I played The Last of Us (on PlayStation 3) with the sub volume cranked up and... WOW, that game is a total trip when you get into it. If you have or ever get a PS3/PS4, it's definitely my #1 recommended game for it. And with that setup in the living room, it was exactly like you describe - I could really hear everything going on in every scene. Without giving too many spoilers here, there is one level where you go into a leaning downtown building, and the creaking that building makes while you're in it is absolutely chilling. Granted the sub/surround system I have is nothing special... but it still works well. Just have to crank it up a bit. This is one reason I can never watch a movie over at my sister's place - they always turn it way down and I can't hear anything most of the time. I don't want to read subtitles if there is audio! So I always crank up the sound when watching movies.

Originally Posted by goodpsusearch

I am now a happy owner of 3 cassette decks:

1)very old rack type single deck, totally dead. Got it for free, will start a thread some day for troubleshooting
edit: found pic of it online:
https://i.ebayimg.com/d/w1600/pict/1...Deck-Mc-11.jpg
but my unit is of black color

2) Marantz SD4050 dual cassette deck, from late 90s. I am quite sure this was not made from Marantz, must be an OEM product that they just slap the name such as Marantz, Pyle, Ion, Pioneer, Teac etc. Seems to be working, might need new belts. Of course the cassette mechanisms are plastic. Supports Dolby B and C. Costed 30 euros

3) Just one week ago, I got a Fisher CR-W345 dual cassette deck along with Fisher MT-345 linear type turntable. Paid 10 euros for both, so I couldn't resist buying them. They were made in the 80s and they were typical Fisher products, made in Japan but relatively cheap. The linear tracking mechanism of the Turntable needs service and the cassette deck needs new belts because the original ones have perished. Will create threads about them too when I find time.

Cool!
Looking forward to seeing these when you get the time.