Technics SU-8077 Rebuild

[Ed Dumas]

Hello Folks,

I am wanting to do a rebuild on a Technics SU-8077 amp that I picked up for cheap, which will educate me on doing this kind of work. I am hoping that this process will prepare me for my ultimate goal of re-building my real amp, which is the SU-8088.

Do you folks have any suggestions on what should be done (which parts should be swapped out), the order of doing the work, or any pitfalls to watch out for? I understand that no one wants to talk about which brand of parts to put back in, as that is a rabbit hole that never seems to end. Okay, no problem.

But, you could include general advice for newbies like me that are learning how to rebuild and upgrade equipment, specifically the Technics SU-8077 for a start. Any photos of work that you might have done pointing to specific parts would also really help!

Looking forward to hearing your thoughts!

Ed

 

[ryuuoh]

This may be of interest:
https://www.reddit.com/r/audiorepair/comments/3cvcn8/technics_su8088_rehab/

 

[Ed Dumas]

That link most definitely helps. Thank you for that!

For those curious, here is the info gleaned from that link. If anyone has a similar list for the Technics SU-8077, that would be a great help as well, as that is where I am going to start.

Cap List for Technics SU-8088

Legend:

BP = Bipolar / Non polar electrolytic

LL = Low leakage current electrolytic

Xn denotes the number of identical caps. For example "50V 1.0uF X7" would mean seven of these caps are present on the board.

HOT indicates the cap is in a location that gets hot. 105°C upgrade suggested.

RWF indicates that the cap is small enough to be replaced with a film type cap like a polyester/mylar type. These are inherently bipolar and low leakage and offer longer service life.

Power Output / Rectifier board:

56V 15000uF X2

100V 470uF X2

Main Amp / Regulator

6.3V 1000uF X2

25V 47uF HOT

50V 1.0uF X5 HOT RWF

50V 47uF X2 HOT

63V 33uF X2 HOT

Protection / Speaker Switch

16V 220uF BP

10V 220uF

6.3V 220uF (protip: Just buy an extra 10V 220uF and place it here.)

50V 3.3uF LL

Tone Stack / Preamp

50V 0.68uF X2 LL RWF

50V 0.68uF X2 BP RWF

50V 3.3uF X2 LL

16V 47uF X2 BP

50V 1.0uF X2 RWF

Meter

50V 1.0uF X2 RWF

6.3V 33uF X2

Headphone Jack + Display Regulator

50V 100uF

25V 33uF

25V 4.7uF X2

50V 2.2uF X2 RWF

EQ Amp / MC Head Amp / Input Selector

6.3V 1000uF X4

16V 100uF BP X2

50V 1.0uF BP RWF X2

50V 100uF

6.3V 220uF X7

25V 100uF X2

50V 47uF X2

35V 33uF X6

6.3V 100uF X4

50V 10uF X2

10V 47uF X6

16V 10uF

50V 1.0uF X2 RWF

If your meters are very dim, check the 2SC1983 NPN darlington transistor on the board with the headphone jack and you will likely find it to be open circuit with either one or both PN junctions missing.

 

[jeromach]

Does the amp still work? And if so, is it ok (or having some minor glitches, which mostly is no real issue to fix)?

There are some things that need to be replaced/done without any question;

To start with, a word of warning; be very very careful with the thermal diodes mounted on the two rear power transistors. Do not bend the leads, they tend to break and the part is nearly impossible to replace (the same goes for the SU-8088, but there they are mounted to the heat sink)

The trimmers right in front of the large filter caps need to be replaced (do NOT - I repeat NOT - try to adjust the old ones, this might blow up the power transistors).
The double transistors 2SA798 and 2SC2291 need to be replaced (Q301, 2, 3 and 4) - you need to use two normal transisors per double transistor and match the new ones (when you're there I can explain how to construct them)
Check all solder connections for bad ones, remove the old solder and apply new.
All switches need to be treated with de-oxit. This does not always work satisfactorily, they then need to be taken apart, cleaned and greased (ask for instructions before dismounting them).
The contacts of the relay need to be cleaned or the relay just replaced

As for the electrolytics, using Nichicon gold for all of them, except the large filter caps, will be ok. Panasonic FM will also do the job nicely.
The large filter caps is optionial if they still measure ok, but if you do not have the tools to do so, it is better to just replace them. Panasonic will be fine, but stocks run out or have done so already, since they stopped producing them. Cornell Dubilier also has nice large filter caps. The diameter is important to fit them in the existing brackets, new caps are smaller, but by just taking a cap with a higher voltage it must be possible to get the correct diameter.

Here's a cap list;

Column 3 and 4 is what is stated in the service manual, column 5 and 6 is what actually came out.

 

[Ed Dumas]

Jeremach, thank you for that excellent info! I appreciate that you have spent some time on this...

I just picked up the SU-8077 today, and it is very clean, and in good working order, albeit original. The man that sold it to me is actually a professional serviceman, and he spent the time to clean it and de-ox the switches and pots, so that is nice. I will hook it up tomorrow, but by the looks of it, it is a clean machine and I did not hear any scratchy noises on dials and things when he played it for me. I will check that out closer, anyway, though.

That is an awesome list above. When I get down to doing those mods, should I go with what is listed in the service manual or what was originally used? From what I have learned elsewhere, raising the voltage of the caps should create no new problems, but could rather avoid problems later on. Is that your take? Thanks.

 

[slimecity]

raising the voltage of the caps should create no new problems, but could rather avoid problems later on. Is that your take?

Increasing the voltage of new caps wont really don't much except leave you with a bigger cap to put in the amp - the same voltage cap as the original cap will generally be a little bit smaller (new ones = more modern = more compact and smaller) than the old caps in your technics.

Good stuff - I have upgraded an 8080 and recently a V6 and I love working in technics units - great service data (have u downloaded a service manual for your amp yet) and both sides of the PCB are usually silk-screened.

 

[Ed Dumas]

Yes, I have downloaded the service manuals for both the 8077 and the 8088, though the 8088 service manual is not scanned very well. I will find another.

I opened up the unit tonight to have a quick look, and I feel much better about doing this work now. Things are reasonably easy to find, and I think I can mostly see how to take the circuit boards out. I am reasonably optimistic to begin, at least to learn now!

"The trimmers right in front of the large filter caps need to be replaced (do NOT - I repeat NOT - try to adjust the old ones, this might blow up the power transistors)." I am not sure what these trimmers look like. I have uploaded a photo with a line to what I think is the trimpots. Can you confirm? What should they be replaced with? Something non-adjustable?

Oh, and the thermal diodes are pretty evident, too. I also found the double transistors you mentioned. Thanks.

 

[MacPhantom]

Yes, these are indeed trimmers.

 

[jeromach]

New caps in the same capacity and voltage can be a whole lot smaller. Mostly that is fine, but it can be an issue when replacing new with old, due to lead holes being too far apart from each other or brackets being too large.

In nearly all cases only bracket mounted caps will pose a problem, if the cap is too small to fit the bracket. I sometimes use 160 volt caps to replace 63 volt caps, just because it will fit the old bracket.

The 8077 btw uses a clamp and it might not be easy to find a proper replacement, since it needs both be wide and high enough. But I just checked what for instance Digi-Key has available and most likely all of these will be ok (I looked at 12k uF too, that would be an upgrade, although probably not really noticeable); http://www.digikey.nl/products/en/c...=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=25

If the diameter of the old caps is 40mm than it would probably be best to take one of 65mm high, then it will probably fit the clamp nicely. Then these two would be the ones to choose;
http://www.digikey.nl/product-detai...nics-cde/383LX103M080N062/338-2034-ND/2256635
http://www.digikey.nl/product-detai...nics-cde/382LX123M080N062/338-2109-ND/2295339

Please take note that all of these are "Radial, Can - Snap-In - 4 Lead" versions, these will fit the existing print without modifications. Also, please check all sizes before ordering, my recollection of sizes might be wrong!

As for the trimmers - (trim pots is the better word I guess ), yes, indeed those on the picture you made. They should be exhanged with similar but new ones. The existing ones very often break down, although they just look fine.

 

[jeromach]

PS: If Digi-Key does not automatically switch the links to the Canadian version, you can replace the .nl part in the link with .ca

And of course there are other suppliers too, like Mouser and Newark Element 14.

However, do not buy caps through eBay, still a lot of those are either fake or do not meet the desired quality standards the larger distributors will all supply.

 

[jeromach]

Jeremach, thank you for that excellent info! I appreciate that you have spent some time on this...
That is an awesome list above. When I get down to doing those mods, should I go with what is listed in the service manual or what was originally used? From what I have learned elsewhere, raising the voltage of the caps should create no new problems, but could rather avoid problems later on. Is that your take? Thanks.

For the largest part, just stick to what the service manual mentions, I just listed the other ones so that you will not be surprised something different comes out. There might be different differences in yours too . As for all less than 25 volt versions I would take 25 volt (or higher). Sometimes higher voltaged caps are even cheaper!

Higher voltage caps indeed might have some longer life, but I would not regard that as a particular benefit when rebuilding these amps, they lasted 40 years in the first place, with the new caps they'll probably last another 40. If at all I would be present at that time, I probably can't recall what I wrote here anwyway...

 

[Ed Dumas]

Thanks Jeromach. I noticed that there were another 4 trimpots on a different board, just to the right of the large black filter caps. I think it was an input board. Should those be replaced as well? Those trimpots look as good as the ones in the above photo.

 

[jeromach]

I did not replace the other ones and I do not think it is necessary. The four you mention are for adjusting the DC offset. There are another four for adjusting the FL power level meter, these also can be left alone.

In the 8088 there is the same issue with the ICQ adjustment trim pots, these too need to be replaced (without attempting to adjust the old ones!), if at least you want your power transistors to live a little longer. These trim pots are different models btw.

 

[MacPhantom]

@jeromach: sorry for thread-hijacking, but now that you mention Icq: how do you adjust this with high power amps?
I have an SE-A3 in which I've aligned everything - except for the level meter (no scope at home, but nvm) and said Icq, as I don't have dummy resistors rated for 300W.

 

[Ed Dumas]

Jeromach, I have another question for you. Before I run out and purchase all those caps that you have listed (thank you again for that list - and I see several good places to purchase them, none of which would have been eBay), are there any there that need to be a cap in a hot spot. I see that Nichicon has some nice audio caps rated for 105C. Do I need those anywhere in that list?

Thanks.

 

[jeromach]

All the old caps are 85C and the amp lasted 35 years, so I do not think it is particularly necessary

I work with Nichicon Muse for nearly all cap needs I have (except the large filter caps) and specifically Nichicon Fine Gold for the regular electrolytics.

But if you would want to go for the very long haul, Panasonic FC would be perfect too (and these are 105).

 

[Ed Dumas]

The only caps on your list that I am having trouble finding are the ones listed at .68uF. Those seem to not be available in either Fine Gold or MUSE from Nichicon. What do you think of this?

http://ca.mouser.com/ProductDetail/...GAEpiMZZMtZ1n0r9vR22bWlSlpQNIMtKvp6yK%2bAlTs=

Or, is there a similar product from a different company that you might know about?

 

[jeromach]

I probably used these (or something similar); http://ca.mouser.com/ProductDetail/WIMA/MKS2C036801E00KSSD/?qs=sGAEpiMZZMv1cc3ydrPrFwgzP98AO9idOj31VloNnOw=

There's no polarity thing with those, they can be mounted either way (like an electrolytic bipolar cap).

Perhaps, when you've made your decision about what to use you could post it here so we can walk it through.

 

[Ed Dumas]

I also found these Pulse X capacitors at ERSE. Note that though the .68uF spec is right, they have an extremely high voltage rating (630 vdc vs 50 vdc), and they are an axial cap instead of a radial cap. They are also non-polar. Can I mount an axial in place of a radial by bending the leads, or is that just Bad Karma? Any thoughts? If that is too weird, then I think I will just go with the film capacitor you suggested above.

 

[slimecity]

Can I mount an axial in place of a radial by bending the leads

Yep - no real issue with this - it just comes down to space and make sure you insulate the lead that you have bent to ensure it doesn't contact with anything else. In this position though I reckon either a film or electrolytic will be fine.