Sansui 7070 questions.

[warriorfan]

reflowing.solder joints has to be easier than 8u baseball right? Is this how anyone.else here relaxes? Was gonna spin some vinyl but my turntable decided to get.noisey. Not lucky and dirty.contacts this time. Poot!

 

[Overundr1]

Before we get too carried away your 7070 is acting like the fuse resistors have gone high z preventing the amplifier card from doing its job. FYI every component on this board is intertwined electrically speaking and if one component drifts out of tolerance the entire apple-cart comes apart and no more output. Sooo, unplug the receiver and pull out the card and lets get some baseline measurements. While I think about it a best practice is NOT to pop the card right back in again as the main caps take a while to discharge, anyways, provide the readings across the following resistors taking note that in some cases there may be some deviation due to parallel circuits. What we are looking for is a reading off the chart compared to nominal values.

R33, 34 180 ohm
R35, 36 4.7 ohm
R39, 40 10ohm
R41, 42 43, 44 150 ohm
R47, 48, 49, 50 4.7 ohm

report back

for extra credit memorize the resistor color code chart before you begin, black brown red--------- lol ok ok you got me I have the chart stuck above the workbench, point is with a chart close to hand its becomes very easy to read the resistor if you cannot find the markings on the board.

-Lee

 

[warriorfan]

Awesome Lee! Be a fun little learning experience. I have a handy little union electrician cheat booklet a buddy gave me and he said I best memorize that chart too! Good stuff and thank you!

 

[avionic]

for extra credit memorize the resistor color code chart before you begin,

Good one ..

 

[avionic]

Awesome Lee! Be a fun little learning experience. I have a handy little union electrician cheat booklet a buddy gave me and he said I best memorize that chart too! Good stuff and thank you!

http://www.resistorguide.com/resistor-color-code-calculator/

 

[warriorfan]

What a darn summer! German cars puking parts at the same time which happened to be right before I was laid off for the winter. Hard to catch up. Life aye?

So I am thinking yesterday I should get this 7070 going. List of resistors and off to radioshack. I go. I get home and look at this dang board one more time and think, yeah me with a soldering iron in one hand and a magnifying glass in the other was gonna be a hot mess.So I sat there kind of bummed yet not willing to quit just yet. Reflow some solder joints. I did the 2624 the board and decided to pull the 2626 board as the emitter resistors on it were getting warm the last time I was pokin around with this. I checked the solder joints on this as well. I was doing this with a bright flashlight. On both the 2624 and 2626 board I could see light through the holes in certain spots. I took notes on which spots I hit. Put her back together with not much faith I had accomplished anything, but to my surprise it works!!!!

I didn't get too crazy in jamming out as I noticed some problems right away. I can only get music by the selector being on the deck positions. Nothing with switch in source mode where it needs to be. Weird! I also have volume with the volume all the way down on the left channel. Right channel seems to be fine.

Should I clean the pots with deoxit before I attempt to set offset and bias or do this first. Since my selector switch is monkey where should I have it set?

Thx yet again fellas!

 

[warriorfan]

Checked dc offset first just to be safe. I got both channels down to .000 Wasn't an easy task as I kept missing the sweet spot. I can now get no change in adjusting bias now and it is a touch high right now sitting a 50mA. Both sides are the same. In adjusting the pots I see only a few mA change in turning the pot each way lock to lock.

It sounds very good and everything runs cool except for the r13 and r14 560ohm 3w ceramic resistors on the f2626 power supply board.Needless to say I am stumped but pleased it is working. Thoughts or guidance would be appreciated. Thx. Ryan

 

[avionic]

I see only a few mA change in turning the pot each way lock to lock.

Check the fuses in your multimeter.

 

[warriorfan]

Check the fuses in your multimeter.

lol avionic! I have seen you post that exact comment more than once. I checked the fuses on all three of the meters I was using. Kind of looks like something is out of spec somewhere for sure. I would like to try to check this across the emittors as I had seen someone else mention but need to make dang sure I know what I am doing beforehand. This thing about killed me last night! Carried it in from the garage and the power cord tripped me. I went down hard and kept the 7070 from hitting the floor.

I fixed the source issue as the knob was off when it was pushed on. I still have faint audio of the left channel with volume down.

Question on the trim pots... Does the value increase by turning clockwise? All seemed to be that way. In doing the bias on the right channel it was oposite. 43mA on left and 44mA on the right. Full sweep of the pots would only get me plus or minus 1mA and I had to turn the pot clockwise on the right to get it down to 44mA.

Kind of want to put this in rotation, but my luck will have it theowing dc at my speakers.

 

[warriorfan]

Is this correct? Measure for 20mA across both sides of r33 for the rigbt side and vice versa on r34 for the other channel for checking bias? Just making sure before I arc weld something.

 

[Hyperion]

Is this correct? Measure for 20mA across both sides of r33 for the rigbt side and vice versa on r34 for the other channel for checking bias? Just making sure before I arc weld something.

You need to measure a voltage - not a current.

Bias current can be measured in two ways - with an ammeter (measuring mA) in line with the power supply to each channel, OR across a resistor, conveniently this can be one or both of the emitter resistors in each channel - but in this case you measure a voltage across the resistor and to calculate what voltage across the emitter resistor you need to know the value of said resistor and how to use Ohms Law to convert the voltage reading, (across the resistor) to a current reading, (through the resistor).

Also don't confuse 'DC Offset' (which will always be a voltage) with Bias current - which can be measured in two ways, as above.

The service manual gives a method of setting bias using the 'in line' (current measuring) method which looks confusing to me.

However, for the required bias current of 30mA, the voltage measurement across one 0.33Ω emitter resistor is 10mV (9.9mV actually but who's counting? ) (that is V = I x R)

 

[warriorfan]

anything look out of the ordinary on the f2624 board here? Rechecking the 14 fused resistors again and will post back.

Two meters I have at my disposal pictured as well.

 

[warriorfan]

You need to measure a voltage - not a current.

Bias current can be measured in two ways - with an ammeter (measuring mA) in line with the power supply to each channel, OR across a resistor, conveniently this can be one or both of the emitter resistors in each channel - but in this case you measure a voltage across the resistor and to calculate what voltage across the emitter resistor you need to know the value of said resistor and how to use Ohms Law to convert the voltage reading, (across the resistor) to a current reading, (through the resistor).

Also don't confuse 'DC Offset' (which will always be a voltage) with Bias current - which can be measured in two ways, as above.

The service manual gives a method of setting bias using the 'in line' (current measuring) method which looks confusing to me.

However, for the required bias current of 30mA, the voltage measurement across one 0.33Ω emitter resistor is 10mV (9.9mV actually but who's counting? ) (that is V = I x R)

yep I shouldn't be doing this. You just twisted my brain hyperion!

 

[avionic]

^^^
What John said..

 

[Hyperion]

You just twisted my brain hyperion!

Drat!!! - just blown my 'do no harm' ticket.

 

[warriorfan]

ok resistors all checked again
r33-208ohm
r34-178ohm
r35-3.8ohm
r36-3.78ohm
r39-.010 ohm
r40-.010ohm
r41-152ohm
r42-153ohm
r43-152ohm
r44-159ohm
r47-.005ohm
r48-.005ohm
r49-.005ohm
r50-.005ohm

I have resistors but not sure if they are correct. First they are carbon film and not metal film. They are 1/2 watt.

 

[warriorfan]

Drat!!! - just blown my 'do no harm' ticket.

Hey I appreciate it all the same! New to this so I expect some to be over my head. Heck the resistor calculator had me stumped the other day when I brought the resistors home. Colors did not match what I had figured up. Think its because they are carbon film instead of metal film? I went through the package and ohm'd each groups until I found the values.

 

[warriorfan]

Pic of my iron. No solder wick or sucker. Can I do this and change out r33,35,36 and 41-44 with out buggering it up worse and leaving it where a tech wont even mess with it? When you guys pull these out how do you go about it? Heat one side and pull out and then the other side? Reverse putting in new. I can solder but this being delicat I want to make sure before I attempt it.

 

[avionic]

Hey I appreciate it all the same! New to this so I expect some to be over my head. Heck the resistor calculator had me stumped the other day when I brought the resistors home. Colors did not match what I had figured up. Think its because they are carbon film instead of metal film? I went through the package and ohm'd each groups until I found the values.

A lot of the new resistors use a 5 band color code rather than a 3 or 4 band color code. 3,4 and 5 band resistor color code calculators can be found "google search" . Regardless if Metal film or Carbon film. Machs Nix.

 

[avionic]

No solder wick or sucker.

I'd use one or the other. Its much easier.