Technics SU-8077 Rebuild
- Thread starter Ed Dumas
- Start date
Bert 1100
Super Member
To be short, there is no need for any heat shrink to the legs. I do not know how you put the two transistors together, but if you do it like below picture, it will fit the holes in the board without any shorts.
Thank you @jeromach so much for this drawing....I'm restoring a Scott 480A with the same 2sa798 / 2sc2291 and I have 60-70mv off DC offset, Ill try with the double matched ksa992 and ksc1845.
When assembling them like in your drawing, does the pinout correspond to the originals ? (BCECB and ECBCE)
Thank you again !
Oh, also, I have in the main amp 2 each of the 2sa798 and 2sc2291. do I need to match all 8 transistors ? or at least the 4 ksa992 and the 4 ksc1845 ? or is it ok to match only pairs for one device ?
Edit : OK, I see from the spec sheets that the pinout does correspond to the originals...nice!
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jeromach
With sufficient thrust, ducks fly just fine
You are welcome Bert 1100. Nice to see where this topic goes 
Yes, the pinouts correspond to the originals when you make them as in the drawing.
As far as I know (and I am also doing it like that!) there is no need to match all 8 transistors to each other, just the ones needed to make new pairs.
The whole concept, where they are used as differential transistors, is that what comes out of it is balanced. DC offset can be both positive and negative, preferably it is zero (mV), something that can be achieved by matching the differential transistors.
The idea behind the double transistor is that by combining the two in one casing there will be a thermal balance between the two, which at the same time takes care of a balanced electrical output (when matched at least).
Yes, the pinouts correspond to the originals when you make them as in the drawing.
As far as I know (and I am also doing it like that!) there is no need to match all 8 transistors to each other, just the ones needed to make new pairs.
The whole concept, where they are used as differential transistors, is that what comes out of it is balanced. DC offset can be both positive and negative, preferably it is zero (mV), something that can be achieved by matching the differential transistors.
The idea behind the double transistor is that by combining the two in one casing there will be a thermal balance between the two, which at the same time takes care of a balanced electrical output (when matched at least).
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Ed Dumas
Member
SUCCESS!!
Today, my thermal compound finally arrived, and I was able to assemble all the last bits of the Technics SU-8077. I built the double transistors using two singles the way Jeromach showed me, and then soldered them in. I also re-installed the power transistors with new Mica insulators and new thermal compound. Checked all the work, and then used the Dim Bulb Tester to carefully power up the amp, keeping my finger on the power switch of the dim bulb tester just in case.
Everything went flawlessly! Bulb went dim, amp lit up, and most importantly, there was no smoke or sparks!! I am very happy.
Then, I adjusted the amp as per the manual. I got the Idling Current to match at 15.5mV, which should be just great. BTW, I also learned that you need to take the amp off the Dim Bulb Tester to adjust it properly, or you do not get proper readings.
Then I powered it up with a pair of Paradigm Mark 5 speakers, and it sounds awesome! Excellent bass, and fantastic spatial imaging. I tested all the functions, and everything works like it should. Looks like it should do well for many years to come.
Thank you Jeromach for all of your sound advice! (Don't think you are the only one that can make a bad pun!) I very much appreciate all of your time helping me out. I owe you.
Next project, my real amp, the Technics SU-8088.
Today, my thermal compound finally arrived, and I was able to assemble all the last bits of the Technics SU-8077. I built the double transistors using two singles the way Jeromach showed me, and then soldered them in. I also re-installed the power transistors with new Mica insulators and new thermal compound. Checked all the work, and then used the Dim Bulb Tester to carefully power up the amp, keeping my finger on the power switch of the dim bulb tester just in case.
Everything went flawlessly! Bulb went dim, amp lit up, and most importantly, there was no smoke or sparks!! I am very happy.
Then, I adjusted the amp as per the manual. I got the Idling Current to match at 15.5mV, which should be just great. BTW, I also learned that you need to take the amp off the Dim Bulb Tester to adjust it properly, or you do not get proper readings.
Then I powered it up with a pair of Paradigm Mark 5 speakers, and it sounds awesome! Excellent bass, and fantastic spatial imaging. I tested all the functions, and everything works like it should. Looks like it should do well for many years to come.
Thank you Jeromach for all of your sound advice! (Don't think you are the only one that can make a bad pun!) I very much appreciate all of your time helping me out. I owe you.
Next project, my real amp, the Technics SU-8088.
Ed Dumas
Member
As per my previous question of using bold type on some items in the parts list of Technics manuals, Tom Bavis suggested that the bold items could have been items recommended for repairmen to stock due to high use. Similar to my thought, but not that nuts and bolts wear out so much as get lost. That does make sense. What do you think?
jeromach
With sufficient thrust, ducks fly just fine
SUPER!!
It always feels great when you've done these open heart surgery kind of things when you finally - wiping off all the sweat from your forehead - power the thing up and you enter nirvana upon the click of the relay.
But, I wouldn't be the bully teacher I am if I did not at least try to cool your enthusiasm a bit, for you to stay humble and human...
What did you do with the relay?
Did you adjust the DC offset (and if so, what was the outcome)?
As for Tom Bavis' suggestion, yes, that sounds plausible. Just only, why wouldn't the fuses be in bold...
It always feels great when you've done these open heart surgery kind of things when you finally - wiping off all the sweat from your forehead - power the thing up and you enter nirvana upon the click of the relay.
But, I wouldn't be the bully teacher I am if I did not at least try to cool your enthusiasm a bit, for you to stay humble and human...
What did you do with the relay?
Did you adjust the DC offset (and if so, what was the outcome)?
As for Tom Bavis' suggestion, yes, that sounds plausible. Just only, why wouldn't the fuses be in bold...
Ed Dumas
Member
Oh, you are not bullying. I appreciate any advice you have, as I am still even learning the terminology. For example, I just learned that "Unbalanced DC Voltage" as used in the manual and "DC offset" are the same thing. Makes sense now that I see the two terms side by side....
Anyway, I adjusted the "Unbalanced DC Voltage" as per the procedure in the manual. I got the left channel to zero, and the closest I could get the right channel was to 5mV. That trimmer pot seems to jump around a lot, so if I touch it, it goes up to 20-30mV, or into the negatives. I figured it would have to do at 5mV, at least for now. With the Subsonic filter on, I got the left channel to 7 mV and the right to 1mV. Again, that seems to be the closest I can do as the pots jump around some.
I am regretting not changing those pots as well, and I think when I put in an order for parts for the SU-8088, I will add more pots to replace these on the 8077 as well. The Bournes pots I put in for adjusting the idle current are certainly a much better pot, and do not jump around like that. Much better to work with, which is why I could get the idle current so close to 15mV and a total left/right match.
Now your question, "What did you do with the relay?" I am not sure what you are asking here. Can you clarify?
Finally, as for the fuses not being in bold in the parts list, I have no idea. Do you think there is anyone at the Panasonic corp today that could answer this question? Technics back then is Panasonic today, is it not? Maybe someone there knows....
Just had a thought. When businesses would become an authorized Technics repair shop, were they expected to purchase a standard kit of parts to begin their stock supply for Technics products when they come in for repair? Maybe the bold list just showed which parts were immediately available in the standard stock kit from Technics, as opposed to a special order which would take some time to get in from Japan back then? Fuses would not be included, because everyone stocked those type of fuses at that time, including literally the local gas station. They were as common as water, so all repair shops already would have had a huge supply of them in stock.
Well, its a thought....
Anyway, I adjusted the "Unbalanced DC Voltage" as per the procedure in the manual. I got the left channel to zero, and the closest I could get the right channel was to 5mV. That trimmer pot seems to jump around a lot, so if I touch it, it goes up to 20-30mV, or into the negatives. I figured it would have to do at 5mV, at least for now. With the Subsonic filter on, I got the left channel to 7 mV and the right to 1mV. Again, that seems to be the closest I can do as the pots jump around some.
I am regretting not changing those pots as well, and I think when I put in an order for parts for the SU-8088, I will add more pots to replace these on the 8077 as well. The Bournes pots I put in for adjusting the idle current are certainly a much better pot, and do not jump around like that. Much better to work with, which is why I could get the idle current so close to 15mV and a total left/right match.
Now your question, "What did you do with the relay?" I am not sure what you are asking here. Can you clarify?
Finally, as for the fuses not being in bold in the parts list, I have no idea. Do you think there is anyone at the Panasonic corp today that could answer this question? Technics back then is Panasonic today, is it not? Maybe someone there knows....
Just had a thought. When businesses would become an authorized Technics repair shop, were they expected to purchase a standard kit of parts to begin their stock supply for Technics products when they come in for repair? Maybe the bold list just showed which parts were immediately available in the standard stock kit from Technics, as opposed to a special order which would take some time to get in from Japan back then? Fuses would not be included, because everyone stocked those type of fuses at that time, including literally the local gas station. They were as common as water, so all repair shops already would have had a huge supply of them in stock.
Well, its a thought....
Ed Dumas
Member
Okay, here is another thought. Manufacturers would possibly have had a local warehouse in various areas around the world to stock new products ready for sale, and also to stock parts for distribution to authorized repair outlets. Maybe the bold list showed what was available at the nearest warehouse as opposed to ordering from the factory back in Japan?
Another possibility....
Another possibility....
jeromach
With sufficient thrust, ducks fly just fine
The DC offset / unbalanced DC voltage etc. etc. 
is perfectly fine. The jumping (which I call dancing) is rather normal, it does not necessarily have to be the trimmer pot, but it might come from the components too. Nothing to worry about and 5 / 7 mV is fine.
As for the relay, it should either be replaced or the contacts should be cleaned. It can cause intermittent sound and distortion if the contacts are burned in or dirty.
It is not so difficult to clean the contacts, the casing of the relay can be removed with two flat (not too big) screwdrivers inserted at the long sides of the cover and the contact rail by removing the small spring (don't loose it!). I use a fibre glass pen for this purpose. Works quite nicely, but you need to take precautions not to let the fibre glass enter your skin or worse, your lungs. When you work carefully it should be save.
I think I now can say without being bold that we have enough plausible theories for the service manual.
is perfectly fine. The jumping (which I call dancing) is rather normal, it does not necessarily have to be the trimmer pot, but it might come from the components too. Nothing to worry about and 5 / 7 mV is fine.As for the relay, it should either be replaced or the contacts should be cleaned. It can cause intermittent sound and distortion if the contacts are burned in or dirty.
It is not so difficult to clean the contacts, the casing of the relay can be removed with two flat (not too big) screwdrivers inserted at the long sides of the cover and the contact rail by removing the small spring (don't loose it!). I use a fibre glass pen for this purpose. Works quite nicely, but you need to take precautions not to let the fibre glass enter your skin or worse, your lungs. When you work carefully it should be save.
I think I now can say without being bold that we have enough plausible theories for the service manual.
Drew Dumas
New Member
Hey all! Just thought I'd chime in. I'm now in possession of the much-discussed SU-8077 in this thread (not by coincidence; OP Ed Dumas is my Dad). It sounds really great! Currently, it's powering a pair of Technics SB-L200's (that Dad also worked on). There is a little bit of crackle in the right speaker. I have yet to determine the source of the crackle. Any thoughts?
Thanks!
Thanks!
Ed Dumas
Member
The DC offset / unbalanced DC voltage etc. etc.
I am quite positive the dancing as you call it, is the trimmer pot, because as I was rotating these trimmers, I could see that they were not moving in a correct arc in the outer shell of the trimmer. They could move a little side to side, and as they did so, you could see the meter jump. I am glad that the levels I got them to is acceptable, though. I could tell that the Bournes trimmers I used elsewhere were vastly better. No side to side motion, and they moved easily and gently round to adjust. I might just want to replace those trimpots at another date, because they are quite easy to do and I am sure I would get a more precise reading after they are replaced.
Drew and I have been in discussion regarding the crackle he is experiencing, and we have isolated it down to one of the speakers that he has. It might be a driver going, a loose speaker cable, or a wire inside the cabinet rubbing on a driver. He is going to check those out.
I elected to leave the relay on the 8077 alone for now. It seems to be working well, and I suspect that it too was cleaned by the serviceman that I got the amp from. But, if you think the relay switch tends to fail over time, then I might also want to replace that soon, too. When I order parts for my SU-8088, I can just include these extra pieces and do it then. I would rather replace it than have it fail later. Is there anything else on this amp that should be considered?
Speaking of relay switches going, I notice on the SU-8077 that the relay takes about 3 seconds or so to turn on. On my main amp, which is the SU-8088, it takes 20-25 seconds to turn on. Does this longer time delay mean that this relay is going?
Ed Dumas
Member
I would like begin to assemble a parts list for my SU-8088 amp, if there is nothing else on the 8077 to do. I can look up all the values now for all the electrolytic caps (I have a service manual, and you have taught me well, Master!). I will also do the trimmers, and I think I will order the relay switch at the same time. I will also do the double transistors, and I have lots of extra pieces now if they are the same part as the 8077 so I should be able to get some matches. I will double check that too.
Are there any other capacitors that should be done as well, such as polyester and polypropylene caps? I understand those are usually quite durable, so if you think they are fine, I will leave them, but I am happy to do them now while I am at it if they should be done. Is there anything else that has a tendency to wear or fail on those units and should be done? I prefer to order all the parts at once in order to save on shipping, which can get very high compared to the cost of the parts.
I was figuring that I would not replace the trimmers for the FL peak meter, as I do not have a Low Frequency Oscillator in order to adjust them afterwards. Though, I might be able to borrow one if you think I should do it...
I appreciate your thoughts!
Are there any other capacitors that should be done as well, such as polyester and polypropylene caps? I understand those are usually quite durable, so if you think they are fine, I will leave them, but I am happy to do them now while I am at it if they should be done. Is there anything else that has a tendency to wear or fail on those units and should be done? I prefer to order all the parts at once in order to save on shipping, which can get very high compared to the cost of the parts.
I was figuring that I would not replace the trimmers for the FL peak meter, as I do not have a Low Frequency Oscillator in order to adjust them afterwards. Though, I might be able to borrow one if you think I should do it...
I appreciate your thoughts!
Ed Dumas
Member
Okay, another question. So many...
Anyway, I was looking up Low Frequency Oscillator for adjusting the FL Peak Meter on the SU-8088 in the event that I decide to replace those trimmers. The Oscillators that I have seen seem to be not very expensive. Is it worth getting one and then doing the trimmers on the SU-8088 after all? Do you have a recommendation of an LFO to use for this?
Anyway, I was looking up Low Frequency Oscillator for adjusting the FL Peak Meter on the SU-8088 in the event that I decide to replace those trimmers. The Oscillators that I have seen seem to be not very expensive. Is it worth getting one and then doing the trimmers on the SU-8088 after all? Do you have a recommendation of an LFO to use for this?
jeromach
With sufficient thrust, ducks fly just fine
20 - 25 seconds to turn on is BAD!
It's not the relay itself, but the underlying circuitry, most likely a bad electrolytic capacitor. You could check the DC on the outputs too (when the relay is engaged of course). If it is too much, do not adjust it before the rebuild.
Do you still use the 8088 on a daily basis? If so, check how much heat it generates, the cover should be a little warm to touch, but not hot. If it is hot, you'd for sure better not use it anymore before the rebuild.
The FL meters normally can be left alone, including the trimmer pots. Only if you notice strange behaviour - for instance; I once had one that always had one segment lit - you should adjust it.
And for the osicillator, not really a need for those anymore nowadays when you have a computer with a sound card or a smartphone with a tone generator app.
Here for instance you find an online tone generator; http://onlinetonegenerator.com/
With the DMM on AC you can adjust the volume to the 0.75 Volt you will need for the adjustment of the 8088 (the 8077 might be the same).
Advise on replacing the relay; relays seldom or never go bad by themselves. The contacts can get burned if there are shorts or too much sparking (only when an amp is in bad condition already) or they can just be dirty. Of course a new relay will prevail any possible shortcoming and it is more convenient, since it will spare you the trouble and working with these pesky fibre glass pens. But it will save you some money servicing the old one and - for the real "vintage" aficionado's, the amp retains a more original look.
I never replace any of the other capacitors nor resistors if they are ok. And they will always be, unless perhaps they were at a spot where something went severly wrong. But even then for instance ceramic capacitors nearly always survive. Resistors is another thing, they can go up or down in resistance when stressed and fuse resistors can break down without showing any damage, but again, fortunately, Technics doesn't use these kind of little devils...
It's not the relay itself, but the underlying circuitry, most likely a bad electrolytic capacitor. You could check the DC on the outputs too (when the relay is engaged of course). If it is too much, do not adjust it before the rebuild.
Do you still use the 8088 on a daily basis? If so, check how much heat it generates, the cover should be a little warm to touch, but not hot. If it is hot, you'd for sure better not use it anymore before the rebuild.
The FL meters normally can be left alone, including the trimmer pots. Only if you notice strange behaviour - for instance; I once had one that always had one segment lit - you should adjust it.
And for the osicillator, not really a need for those anymore nowadays when you have a computer with a sound card or a smartphone with a tone generator app.
Here for instance you find an online tone generator; http://onlinetonegenerator.com/
With the DMM on AC you can adjust the volume to the 0.75 Volt you will need for the adjustment of the 8088 (the 8077 might be the same).
Advise on replacing the relay; relays seldom or never go bad by themselves. The contacts can get burned if there are shorts or too much sparking (only when an amp is in bad condition already) or they can just be dirty. Of course a new relay will prevail any possible shortcoming and it is more convenient, since it will spare you the trouble and working with these pesky fibre glass pens. But it will save you some money servicing the old one and - for the real "vintage" aficionado's, the amp retains a more original look.
I never replace any of the other capacitors nor resistors if they are ok. And they will always be, unless perhaps they were at a spot where something went severly wrong. But even then for instance ceramic capacitors nearly always survive. Resistors is another thing, they can go up or down in resistance when stressed and fuse resistors can break down without showing any damage, but again, fortunately, Technics doesn't use these kind of little devils...
Ed Dumas
Member
I do not use the 8088 on a daily basis, but once or twice per week. It gets warm, but not terribly hot. I have a rather unique sound system that has pretty much nothing as vintage and unchanged. Everything has been modified, to some degree, to achieve a sound that I am looking for. The 8088 has only been modified by using a Music Fidelity tube buffer in the pre-out/main ins position. But, that tube buffer has also been modified with a Rock Grotto upgrade kit and a proper transformer instead of the digital wall-wart.
Would this tube buffer cause a delay in the amp relay firing? Does the tube buffer have to warm up first? I will check the relay time on the 8088 when I remove it from my system, and I am okay having this system down for a couple of weeks while I do the work.
As for changing the relay, I am totally okay with that, too. If it saves problems later, I would rather do it. The cost of the part is not huge, but the shipping of each individual part can be high. I would rather add on the part now while I am paying for the shipping already. Can you tell me which part you used for that? I looked some up, and was not sure which way to go.
For the rest of the caps, that sounds good. I will have a look at them when I open the case and see if anything looks bad before I order. Thanks again!
Would this tube buffer cause a delay in the amp relay firing? Does the tube buffer have to warm up first? I will check the relay time on the 8088 when I remove it from my system, and I am okay having this system down for a couple of weeks while I do the work.
As for changing the relay, I am totally okay with that, too. If it saves problems later, I would rather do it. The cost of the part is not huge, but the shipping of each individual part can be high. I would rather add on the part now while I am paying for the shipping already. Can you tell me which part you used for that? I looked some up, and was not sure which way to go.
For the rest of the caps, that sounds good. I will have a look at them when I open the case and see if anything looks bad before I order. Thanks again!
Drew Dumas
New Member
Update on the "crackle" mentioned earlier upon testing the SU-8077:
There was a flaw in my test LP. Sounded a lot like speaker was crackling, when really it was just doing its job very well! Changed to a different LP, crackle is gone and the SU-8077 sounds marvellous. Rookie mistake. D'oh!
On another note: I'm disappointed that the record is flawed because it's brand spanking new, and I backed the recording project. You'd think they'd at least send me a good record.
Consider this post "un-hijacked." Now, on with the SU-8088 rebuild! Can't wait to read about it!
There was a flaw in my test LP. Sounded a lot like speaker was crackling, when really it was just doing its job very well! Changed to a different LP, crackle is gone and the SU-8077 sounds marvellous. Rookie mistake. D'oh!
On another note: I'm disappointed that the record is flawed because it's brand spanking new, and I backed the recording project. You'd think they'd at least send me a good record.
Consider this post "un-hijacked." Now, on with the SU-8088 rebuild! Can't wait to read about it!
Ed Dumas
Member
Ed Dumas
Member
Okay, I have some very interesting readings from my SU-8088 amp. Note that I did not adjust anything, just wrote down some measurements.
First, I measured the relay response without all the bells and whistles on the amp, which includes the tube buffer, tube phono stage, and all the input pieces. That relay response was 3 seconds. Much better than the 20-25 secs when it is all connected up.
Then, for "Constant Voltage Power Supply" it is reading +31.5 volts, when it should read +48 volts. This is dramatically undercurrent, and is probably not a good sign. That is between terminal 152 and ground. Going from terminal 153 to ground reads -31.25 volts. Consistent, but not good. Does this mean that the filter caps are going? I am going to replace them all anyway.
For DC offset, the left channel reads 26 mV and the right channel reads 79 mV. These are also not very good considering that they are supposed to be 0. The amp was in for some significant service about 2 years ago, which included some adjusting. I guess it has gone out since then?
For idling current, it is reading at 10mV on the left, and 9 mV on the right when it should be 15 mV. That is probably a symptom of the undercurrent above. I guess under is better than over?
Interesting to hear any comments you folks might have.
First, I measured the relay response without all the bells and whistles on the amp, which includes the tube buffer, tube phono stage, and all the input pieces. That relay response was 3 seconds. Much better than the 20-25 secs when it is all connected up.
Then, for "Constant Voltage Power Supply" it is reading +31.5 volts, when it should read +48 volts. This is dramatically undercurrent, and is probably not a good sign. That is between terminal 152 and ground. Going from terminal 153 to ground reads -31.25 volts. Consistent, but not good. Does this mean that the filter caps are going? I am going to replace them all anyway.
For DC offset, the left channel reads 26 mV and the right channel reads 79 mV. These are also not very good considering that they are supposed to be 0. The amp was in for some significant service about 2 years ago, which included some adjusting. I guess it has gone out since then?
For idling current, it is reading at 10mV on the left, and 9 mV on the right when it should be 15 mV. That is probably a symptom of the undercurrent above. I guess under is better than over?
Interesting to hear any comments you folks might have.
The Fuxtor
Addicted Member
I
Need to recap the power supply for sure and sounds like the protection circuit too.
I just fixed a Sansui Quad that had no relay whatsoever, it was due to 3 capacitors that were dragging the voltage down causing too little voltage for the relay to engage....20 - 25 seconds to turn on is BAD!
It's not the relay itself, but the underlying circuitry, most likely a bad electrolytic capacitor. You could check the DC on the outputs too (when the relay is engaged of course). If it is too much, do not adjust it before the rebuild.
Do you still use the 8088 on a daily basis? If so, check how much heat it generates, the cover should be a little warm to touch, but not hot. If it is hot, you'd for sure better not use it anymore before the rebuild.
The FL meters normally can be left alone, including the trimmer pots. Only if you notice strange behaviour - for instance; I once had one that always had one segment lit - you should adjust it.
And for the osicillator, not really a need for those anymore nowadays when you have a computer with a sound card or a smartphone with a tone generator app.
Here for instance you find an online tone generator; http://onlinetonegenerator.com/
With the DMM on AC you can adjust the volume to the 0.75 Volt you will need for the adjustment of the 8088 (the 8077 might be the same).
Advise on replacing the relay; relays seldom or never go bad by themselves. The contacts can get burned if there are shorts or too much sparking (only when an amp is in bad condition already) or they can just be dirty. Of course a new relay will prevail any possible shortcoming and it is more convenient, since it will spare you the trouble and working with these pesky fibre glass pens. But it will save you some money servicing the old one and - for the real "vintage" aficionado's, the amp retains a more original look.
I never replace any of the other capacitors nor resistors if they are ok. And they will always be, unless perhaps they were at a spot where something went severly wrong. But even then for instance ceramic capacitors nearly always survive. Resistors is another thing, they can go up or down in resistance when stressed and fuse resistors can break down without showing any damage, but again, fortunately, Technics doesn't use these kind of little devils...
Need to recap the power supply for sure and sounds like the protection circuit too.
Drew Dumas
New Member
Surprised to hear how "out of whack" those readings are for a couple reasons. A: It's had very little use since the servicing it received. B: It still sounds really good! Perhaps the servicing was not as extensive as you were lead to believe... 