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Sansui Eight help - hum on one channel

Progress was made today. The current state had been that I was getting about 35V DC offset at speaker terminals. Both channels seemed to be affected equally. The only configuration that gave a difference in the two channels was with F005 and F006 pulled and no driver boards in. Then I was getting offset of -24V on L channel and 0.3 V on R channel.

So, in this configuration with pre-out and power-in separated (jumpers pulled and speaker output set to C) I swapped TR855 and 856 (2SA566) to see if the higher DC offset from L channel would move to R. No change. Then swapped TR853 and 854 (2SC680). No change.

Next decided to measure the pin voltages for all connectors with the driver boards out on both channels. Significant differences marked with an arrow.

Pin, L, R
P, 51, 51.9
O, 0, 0
N, 0, 0
M, -1.7, 0.17 <--
L, -1.6, 0.18 <--
K, -1.7, 0.26 <--
J, 42.7, 42,7
I, -4.3, -4.0
H, -27.5, 0.9 <--
F, -42.2, -42.0
E, -42.7, -42.4
D, -0.16, -0.5 <--
C, 0, 0
B, -50.2, -49.9
G, 0, 0
A, 0, 0

So, MLK are BCE of TR853; however, since I swapped TR853 and 854, I focused on TR857 since K is also base voltage for this transistor and H is connected to the emitted through a cement resistor.

Took ECB readings on TR857 and TR858 for comparison:

TR857, -42.2, -28, -42.5
TR858, 0, 42.6, 1.06

Seemed like TR857 was bad (Sony 2SD88A), so pulled that and replaced with the one good 2SC1079 I had on hand. (I tested the Sony with my transistor meter, and it tested ok.)

Turned back on and 8H is reading 0V on both channels. :thumbsup:

Decided to put fuses F005 and F006 back in, still getting offset of 0V. :thumbsup:

Decided to put R channel driver board in. Got 27V at speaker C out. :(

Took the same driver board and put in L side, 27V output but then R839 smoked. :eek:

That resistor connects pins F and E, which is B9 power supply and TR855 C.

Realized I probably should have checked all pins for driver boards before putting the board back in. :oops:

So, with F005 and 6 back out, checked all pin voltages.

Pin, L, R
P, 49.1, 49.2
O, 0, 0
N, 0, 0
M, 4.2, 0.16 <--
L, 4.2, 0.18 <--
K, 4.4, 0.24 <--
J, 40.5, 40.7
I, 27.9, -9.0 <--
H, 39.4, 0.76 <--
F, 39.5, -40.2 <--
E, -40.5, -40.5
D, 39.9, -0.9 <--
C, 0, 0
B, -47.5, -47.8
G, 0, 0
A, 0, 0

So, MLK are BCE of TR853/854 and IFD are ECB of TR855/856.

I'm at the point where I think all of these transistors along with OT need to be replaced. They test ok on my transistor test meter and do not test shorted on my DMM diode setting, but these voltage readings do not look good. What are the replacements for TR853/854 and TR855/856?

On the positive side, all of the PS voltages have come down from before changing TR857.

I also assume that it is not OK to use 2SC1079 in TR857 and 2SD88A in TR859 as these are differently rated transistors? Probably should have thought about that before putting the driver board in on the L channel.
 
KeithD said:
What are the replacements for TR853/854 and TR855/856?
Click to expand...
These are TO-66 case transistors, so for TR853/854 = 2SC680 (NPN) the replacement is MJE15032G (NPN)
and for TR855/856 = 2SA566 (PNP) the replacement is MJE15033G (PNP)

Note that these replacements are a TO-220 package, which was designed so they could be used as TO-66 replacements, so you will need TO-220 mica washers for them as well. (you may need an 'insulating set'? - which also includes insulating bushes). Note well that the tab of the TO-220 device is the collector which must be insulated from the chassis.
KeithD said:
I also assume that it is not OK to use 2SC1079 in TR857 and 2SD88A in TR859 as these are differently rated transistors?
Click to expand...
At this stage it's fine to use them, but I would try to make sure you use the same type for all four when you get all the troubles ironed out.

I can tell you are beginning to 'feel this problem out' - well done, keep it up. :thumbsup:
 
Hyperion said:
These are TO-66 case transistors, so for TR853/854 = 2SC680 (NPN) the replacement is MJE15032G (NPN)
and for TR855/856 = 2SA566 (PNP) the replacement is MJE15033G (PNP)

Note that these replacements are a TO-220 package, which was designed so they could be used as TO-66 replacements, so you will need TO-220 mica washers for them as well. (you may need an 'insulating set'? - which also includes insulating bushes). Note well that the tab of the TO-220 device is the collector which must be insulated from the chassis.
Click to expand...
OK, thanks for those recommendations. So, would one normally mount these laying flat on a mica insulator? I assume you would clip the center pole off and use the top tab as collector putting a screw through that and the mica insulator into one of the the threaded holes the the TO-66 transistors were screwed into. Then, you'd have to bend the E and B legs 90 degrees to fit into the holes for them. Is that what people usually do?
 
KeithD said:
I assume you would clip the center pole off and use the top tab as collector putting a screw through that and the mica insulator into one of the the threaded holes the the TO-66 transistors were screwed into. Then, you'd have to bend the E and B legs 90 degrees to fit into the holes for them. Is that what people usually do?
Click to expand...
Yes, that's exactly right. ;)
 
Exactly as John says, flat mica washers, cut off the middle (collector) - I've done this in two amps. Here is a post I shared so you can see what it looks like. Now, AK member Kale shows a more professional way to implement this, and I think John has a better way as well. I will say that I have never had any issues or hot drivers - in my opinion the legs you do insert fits very firmly, so as long as you carefully check your work - continuity check that mica is seated correctly - this simply method will get the job done and as you can read I firmly believe, especially with the Eight, that this combo is better than original - it is certainly way more robust as well.
 
OK, starting to develop a BOM of parts. Besides the OTs and driver transistors, what else should I be looking at ordering to have on hand? There are only 4 caps on the driver boards. I've got
MKS4B041002C00JF00 1µF/50V on hand that should work for C801. What is recommended for C802? I don't have any 10µF caps with that high of voltage rating.

Not sure I want to tackle the PS board, but might be prudent to order the parts. What are the recommended e-cap replacements, or which line of Nichicon caps should I be looking at? Would you recommend upping the voltages from spec? Any transistors I should make sure I have on hand?
 
OK, when I worked on some of the Pioneer gear I had, seemed like all the BOMs used Nichicon UPW for most applications, with UKL for some of the small caps. I still have a lot of those on hand, but Sansui used caps with higher voltage ratings than Pioneer, so there's not a lot of overlap.
 
KeithD said:
OK, when I worked on some of the Pioneer gear I had, seemed like all the BOMs used Nichicon UPW for most applications, with UKL for some of the small caps. I still have a lot of those on hand, but Sansui used caps with higher voltage ratings than Pioneer, so there's not a lot of overlap.
Click to expand...
'PW' would be low ESR, 'KL' would be low leakage, very important, in my opinion for the best results, to find 'right capacitor right place' - then you will extract the best SQ out of the restored gear.

Anything that observes the value and voltage will work well, but for that extra few percent.........
 
Hyperion said:
'PW' would be low ESR, 'KL' would be low leakage, very important, in my opinion for the best results, to find 'right capacitor right place' - then you will extract the best SQ out of the restored gear.

Anything that observes the value and voltage will work well, but for that extra few percent.........
Click to expand...
Yes, and this is where I am lacking in knowledge/skills. In the past I have followed BOMs posted in the Pioneer forum, but that does not appear to be the "culture" in the Sansui forum. I do not have the necessary knowledge/background to determine the best cap for each location, hence my question. I did ask before about a BOM for the Eight, but it doesn't seem to exist. I don't need to order caps for the PS, but thought it would be a good idea.

Also, should probably replace the trimmers on the driver boards. What have others used for those?
 
We do share some list on occasion, but the thing about Sansui is that they often changed parts/values during a production run. Besides, you already have a BOM.....board by board in the SM. Then you simply copy that, and then board by board verify if it matches your particular unit. There aren't many caps so this is easy to do, the more time consuming part is writing down all the long part numbers and then building your purchase list.

You could recap the entire thing just using Nichicon finegold, just like Sansui only used the same grey Elnas - it wasn't until a few years after the Eight, that Sansui began to use different colored caps based on their duty (power supply, signal, coupling etc) I honestly wouldn't worry too much about that part, the sound is already build into the design. By using dedicated caps for various positions you might gain a tiny bit longevity or a tiny bit better detail in a specific freq range.....but likely beneath anything you could credible discern in a blind test. However many of us use this formular:

Tone board: Elna Silmic II
Power supply: Nichicon UPW
Equalizer (phono board): Elna Silmic II
Driver board Nichicon audiograde KG, KZ or Finegold, and a wima in the C801 position.

That's it. Can't go wrong. Once it's up and running you can always revisit it later and try a tweak here and there, with the benefit of now having established a Sonic baseline - that's the fun part.
 
stereofun said:
We do share some list on occasion, but the thing about Sansui is that they often changed parts/values during a production run. Besides, you already have a BOM.....board by board in the SM. Then you simply copy that, and then board by board verify if it matches your particular unit. There aren't many caps so this is easy to do, the more time consuming part is writing down all the long part numbers and then building your purchase list.

You could recap the entire thing just using Nichicon finegold, just like Sansui only used the same grey Elnas - it wasn't until a few years after the Eight, that Sansui began to use different colored caps based on their duty (power supply, signal, coupling etc) I honestly wouldn't worry too much about that part, the sound is already build into the design. By using dedicated caps for various positions you might gain a tiny bit longevity or a tiny bit better detail in a specific freq range.....but likely beneath anything you could credible discern in a blind test. However many of us use this formular:

Tone board: Elna Silmic II
Power supply: Nichicon UPW
Equalizer (phono board): Elna Silmic II
Driver board Nichicon audiograde KG, KZ or Finegold, and a wima in the C801 position.

That's it. Can't go wrong. Once it's up and running you can always revisit it later and try a tweak here and there, with the benefit of now having established a Sonic baseline - that's the fun part.
Click to expand...
Thanks Tom. This is exactly what I was looking for!

Any recommendation on the trimmers?

(By the way, I think all of the e-caps in my Eight are Chemi-Con.)
 
KeithD said:
Any recommendation on the trimmers?
Click to expand...
I always use Bourns multi-turn types, but they can be a bit tricky to find on the Mouser website if you don't get the search exactly right - this freaked me out a couple of times. ;)

Getting the new trimmer with the correct adjuster orientation is the trick, you want to be able to reach every trimmer with the unit assembled. :)

I could give you part numbers - but I need to see how the old ones are orientated with reference to the innards of the 'Eight'. - and I would need the values of the ones in your unit now...
 
Thanks John, if you look way back to post #11, I've got pictures there of the two driver boards. The adjustment is facing up when the board is mounted.

According to SM VR801 = 100 kohm, VR802 = 3 kohm, VR803 = 1 kohm, VR804 = 3 kohm. I can double check these visually later today.

One thing to note, SM says VR802 minimum is counterclockwise, while VR803 minimum is clockwise.
 
KeithD said:
SM says VR802 minimum is counterclockwise, while VR803 minimum is clockwise.
Click to expand...
This is one thing you won't be able to rely on if you fit multi-turn replacements, it's not 'clear cut' anyway.

Best way round this is measure with a multimeter (on Ω) - to make sure you have the 'slider' at the correct end of the track. ;)

If you are happy with that, I'll try to get you those P/Nos - please indicate ;)

I'll also wait for you to check the values....
 
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OK, will check those out.

Both Mouser and Digikey have backorder on driver transistors. Digikey should have stock in a couple of weeks, Mouser in September.
 
Took a bunch of readings on the VRs on one driver board. Common was connected to the center pin, and measured resistance with + probe on left and right pin of each. Turned trimmer to the end clockwise (CW) and counter clockwise (CCW).

VR, pin, CW, CCW

801, R, 105kΩ, 50Ω
801, L, 0.18Ω, 0.3Ω

802, R, 3.4kΩ, 430Ω
802, L, 360Ω, 3.4kΩ

803, R, 1.4kΩ, 139Ω
803, L, 167Ω, 1.4kΩ

804, R, 3.2kΩ, 0.48kΩ
804, L, 3.7Ω, 3.3kΩ

Everything is pretty much symmetrical on the L and R pins of each VR except for VR801 L pin. Is this normal, or does it indicate there is a problem with this VR?

Will check 801 on the other driver board.
 
Just checked VR801 on other driver board:

801, R, 108kΩ, 0.30Ω
801, L, 0.11Ω, 0.11Ω

On the L pin, the resistance did not change at all as I move the trimmer.
 
KeithD said:
Everything is pretty much symmetrical on the L and R pins of each VR except for VR801 L pin. Is this normal, or does it indicate there is a problem with this VR?
Click to expand...
Unlike the other VR's VR801 has the slider connection shorted to one end of the track (grounded) - so the readings you are getting are as expected.

What your readings do show is that the trimmers (at least for the first driver board) are in fairly poor condition, which bears out what one member has advised, namely to replace the trimmers - advice that I always recommend as well - it's well worth it. ;)

So, it is:-

VR801 = 100K = https://www.mouser.co.uk/ProductDetail/Bourns/3296P-1-104LF?qs=sGAEpiMZZMvygUB3GLcD7gTIXvDhNlCg9GiTl4mjHak=
VR802 = 3.3K = https://www.mouser.co.uk/ProductDetail/Bourns/3362X-1-332LF?qs=sGAEpiMZZMvygUB3GLcD7pHZXFT4%2BxRqtL8V4SdZnNunmsQ7wrf%2BSw==
VR803 = 1K = https://www.mouser.co.uk/ProductDetail/Bourns/3296P-1-102LF?qs=sGAEpiMZZMvygUB3GLcD7sSg8po3Zpo3SFK5pM%2Bfyvs=
VR804 = 3.3K = https://www.mouser.co.uk/ProductDetail/Bourns/3362X-1-332LF?qs=sGAEpiMZZMvygUB3GLcD7pHZXFT4%2BxRqtL8V4SdZnNunmsQ7wrf%2BSw==

VR801 & VR803 are Bourns 3296P multi-turn

for VR802 & VR804 the choices are more limited, because of the resistance value - so I had to go with Bourns 3362X single turn.

If you want to go with single turn for all here are the other part numbers:-
VR801 = 100K = https://www.mouser.co.uk/ProductDetail/Bourns/3362X-1-104LF?qs=sGAEpiMZZMvygUB3GLcD7l39JMs///LO%2BnhxvbW1FC8=
VR803 = 1K = https://www.mouser.co.uk/ProductDetail/Bourns/3362X-1-102LF?qs=sGAEpiMZZMvygUB3GLcD7oqoMetRlnqQOShOgWLPHqY=

The Bourns 3362X are physically quite small, so you just might have to extend the wire leads, this is not ideal, so if anyone has the part numbers of the trimmers they used - please post them up. ;)
 
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Great, thanks John. I will order those unless someone posts something that would work better.
 
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