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My first receiver restoration attempt: G-6700.
- Thread starter ghazzer
- Start date
ghazzer
Senior Member
WOW, that's quite an offer ! ! ! I'll be back this summer for my 50th high school reunion and I'll plan for a little jaunt down your way.
The G-6700 restoration is on the back burner again. We had new tile put down in the foyer and I want a nice oak trim piece to transition down to the carpeted steps rather than a cheap aluminum strip. So, now I hafta get out the router table and make one. A local mill wanted $150 to make one, and could not guarantee what I wanted. Yesterday I got some ½"X2" strips of popular and will do a trial run to see if my concept will work. Somehow or the other my wife thinks that finishing the foyer floor is more important than the Sansui.
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The G-6700 restoration is on the back burner again. We had new tile put down in the foyer and I want a nice oak trim piece to transition down to the carpeted steps rather than a cheap aluminum strip. So, now I hafta get out the router table and make one. A local mill wanted $150 to make one, and could not guarantee what I wanted. Yesterday I got some ½"X2" strips of popular and will do a trial run to see if my concept will work. Somehow or the other my wife thinks that finishing the foyer floor is more important than the Sansui.
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ghazzer
Senior Member
Error in schematic???
Earlier this week I was replacing C25 in the driver circuit and I looked back at the schematic to verify that I had the polarity right, when I realized that the schematic does not agree with the PCB. The PCB has the + terminal of C25 connected to the wiper of VR03 while the schematic shows the wiper tied to the - terminal. I chased my tail on this for a while until I finally looked at the schematics for the G-7700 and the G-5700 (all in same manual, and provided in the attached WORD document).
The circuitry is almost identical for all 3 receivers, but the schematic for the G-6700 shows the two lines going out to D701 as reversed from the schematics (and 6700 PCB). The 6700 schematic shows VR03 and R37 going out to the cathode of D701, not the anode as is shown for the other two.
The same is true for the right channel as well.
I'd just like to know if anyone else has been down this path, or I have wandered off the deep end.
G-6700 REVISED schematic
This revised schematic has reversed the two lines (within red line) so that it agrees with the PCB that I have, and the schematics for the 7700 & 5700. The circuitry within the blue line was drawn in the power supply area but I drew it here for relevance.
Also: Can anyone tell me what the abbreviation "BRN" means next to C25? I don't think brown is the answer.
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Earlier this week I was replacing C25 in the driver circuit and I looked back at the schematic to verify that I had the polarity right, when I realized that the schematic does not agree with the PCB. The PCB has the + terminal of C25 connected to the wiper of VR03 while the schematic shows the wiper tied to the - terminal. I chased my tail on this for a while until I finally looked at the schematics for the G-7700 and the G-5700 (all in same manual, and provided in the attached WORD document).
The circuitry is almost identical for all 3 receivers, but the schematic for the G-6700 shows the two lines going out to D701 as reversed from the schematics (and 6700 PCB). The 6700 schematic shows VR03 and R37 going out to the cathode of D701, not the anode as is shown for the other two.
The same is true for the right channel as well.
I'd just like to know if anyone else has been down this path, or I have wandered off the deep end.
G-6700 REVISED schematic
This revised schematic has reversed the two lines (within red line) so that it agrees with the PCB that I have, and the schematics for the 7700 & 5700. The circuitry within the blue line was drawn in the power supply area but I drew it here for relevance.
Also: Can anyone tell me what the abbreviation "BRN" means next to C25? I don't think brown is the answer.
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ghazzer
Senior Member
This pic shows C25 from the F2980 board, taken in sunlight. This cap is marked "BRN" in the schematic but is clearly orange when compared to the brown rectangle below it. I don't know what the "(M)" signifies, or the
90 (S) in the next pic. This one was taken indoors in fluorescent lighting.
Most threads that I have read support the theory that "BRN" somehow indicates a low noise or low leakage cap, and that most of today's Quality caps will meet or exceed those requirements from the 1970s. I have installed KL series Nichions (647-UKL1H010KDDANA from Mouser) and am hoping that everything is copasetic.
90 (S) in the next pic. This one was taken indoors in fluorescent lighting.
Most threads that I have read support the theory that "BRN" somehow indicates a low noise or low leakage cap, and that most of today's Quality caps will meet or exceed those requirements from the 1970s. I have installed KL series Nichions (647-UKL1H010KDDANA from Mouser) and am hoping that everything is copasetic.
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This pic shows C25 from the F2980 board, taken in sunlight. This cap is marked "BRN" in the schematic but is clearly orange when compared to the brown rectangle below it. I don't know what the "(M)" signifies, or the
90 (S) in the next pic. This one was taken indoors in fluorescent lighting.
Most threads that I have read support the theory that "BRN" somehow indicates a low noise or low leakage cap, and that most of today's Quality caps will meet or exceed those requirements from the 1970s. I have installed KL series Nichions (647-UKL1H010KDDANA from Mouser) and am hoping that everything is copasetic.
The Sansui Common Parts List designates orange capacitors as "low noise"
As Lee has advised, the KL's are a good choice.
Cheers
John
ghazzer
Senior Member
First, I recently learned that the "M" on the cap above indicates a 20% tolerance. "K" =10% and J = 5%. I replaced it with a 10%.
Believe it or not, I have finally finished replacing parts on the F-2980 board. I replaced ALL of the caps, resistors, trimpots and transistors in the driver section, all of the electrolytic caps in the P/S, and the four output transistors on the F-3058 boards. I checked each part as it was removed to make sure I was replacing it with the correct value. I found several values that did not agree with the schematic.
The 3058 boards had some burnt and lifted tracks and I was lucky enough to find a pair of replacements on fleabay. The STV-3H diodes were good on those. I replaced the output TRs with NJW0281s and NJW0302s. {P1030504} {P1030505}
Some of the jumpers had to be replaced so I used 0.063" molex pins to replace the mounting pins on the ends. I bent the small tabs back so the pins will not sink thru the holes. {P1030501}
Now I want to temporarily replace the 0.33Ω emitter resistors with 100Ω, 5W loads to protect the output TRs when I bring it up on a DBT.
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Believe it or not, I have finally finished replacing parts on the F-2980 board. I replaced ALL of the caps, resistors, trimpots and transistors in the driver section, all of the electrolytic caps in the P/S, and the four output transistors on the F-3058 boards. I checked each part as it was removed to make sure I was replacing it with the correct value. I found several values that did not agree with the schematic.
The 3058 boards had some burnt and lifted tracks and I was lucky enough to find a pair of replacements on fleabay. The STV-3H diodes were good on those. I replaced the output TRs with NJW0281s and NJW0302s. {P1030504} {P1030505}
Some of the jumpers had to be replaced so I used 0.063" molex pins to replace the mounting pins on the ends. I bent the small tabs back so the pins will not sink thru the holes. {P1030501}
Now I want to temporarily replace the 0.33Ω emitter resistors with 100Ω, 5W loads to protect the output TRs when I bring it up on a DBT.
.
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ghazzer
Senior Member
I have replaced the 0.33Ω emitter resistors with 100Ω(5) to protect the output transistors when I apply power for the first time in months. I re-connected all the jumpers and double checked continuity between the next points outboard of the jumpers. {P1030569}
I also added some 8Ω(50) load resistors at the speaker terminals, and will ensure that they are not touching at power up. Will be using a DBT starting with a 60 watt bulb.
I will follow the same procedures I used back in January, on pages 4&5. {P1030570}
Next precaution will be to take the receiver outside and wash the PCB with contact cleaner and a small brush, then blow it off to get rid of any solder flecks that may have been left behind. It is cold, windy, rainy and dreary today, so I'll wait for a better day.
I have centered the 25 turn Bourne style pots I used for trimmers. I bought some crimp on connectors with 1/16" pins that I think will work well as test points for the bias and offset adjustments, so I need to go install them now.
Please tell me if you can think of anything else I should do or check before powering it up.
I also added some 8Ω(50) load resistors at the speaker terminals, and will ensure that they are not touching at power up. Will be using a DBT starting with a 60 watt bulb.
I will follow the same procedures I used back in January, on pages 4&5. {P1030570}
Next precaution will be to take the receiver outside and wash the PCB with contact cleaner and a small brush, then blow it off to get rid of any solder flecks that may have been left behind. It is cold, windy, rainy and dreary today, so I'll wait for a better day.
I have centered the 25 turn Bourne style pots I used for trimmers. I bought some crimp on connectors with 1/16" pins that I think will work well as test points for the bias and offset adjustments, so I need to go install them now.
Please tell me if you can think of anything else I should do or check before powering it up.
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Can you bring it up slowly on a Variac?
I smoked the family turkey today in cold rainy weather. By the end I was wet from head to foot. But the bird was beautiful!
I smoked the family turkey today in cold rainy weather. By the end I was wet from head to foot. But the bird was beautiful!
petehall347
the brandy coffee man
turn the bias pots to minimum ...offsets to centre
ghazzer
Senior Member
Yes. I went back and checked my notes and those agree with minimum & middle. Just need to use the notes and forget about my memory.
Like Grainger, I've been drafted to help my wife get ready for the big meal tomorrow. Sweet tater casserole is ready to pour into the crock pot. Made the cornbread yesterday and crumbled it this morning. Just have to sauté some onions and celery, add chicken broth, chopped pecans & spices, squish it all together and the dressing will be ready for the oven.
We got a fresh turkey this year and I sure don't miss all the crap about thawing the bird.
Now I can think about some background music for tomorrow. Wonder how James Brown will go with Butterball???
Here's hoping that everyone can relax tomorrow and enjoy the company and good food - - -
Like Grainger, I've been drafted to help my wife get ready for the big meal tomorrow. Sweet tater casserole is ready to pour into the crock pot. Made the cornbread yesterday and crumbled it this morning. Just have to sauté some onions and celery, add chicken broth, chopped pecans & spices, squish it all together and the dressing will be ready for the oven.
We got a fresh turkey this year and I sure don't miss all the crap about thawing the bird.
Now I can think about some background music for tomorrow. Wonder how James Brown will go with Butterball???
Here's hoping that everyone can relax tomorrow and enjoy the company and good food - - -
ghazzer
Senior Member
Bias adjustment
The trimmers (VR01&02) for the DC offset were simple to install because they are adjusted to minimize the DC at the speaker terminals by balancing the differential inputs. The direction to be turned to increase or decrease the bias will reverse if you cross to the other side of the balance point.
I replaced the single turn pots with 25 turn bourn style pots to allow for finer adjustments. 5 turn pots would have been AOK, but 25 turn pots are easier to find. Using a spare trimmer I turned it CCW 30 times to make sure that I was at the low end (0.6Ω to 98.4Ω), and found that it takes about 2 turns to get the wiper back in contact with the element and start increasing the value. So, I went back to the trimmers installed on the PCB and gave them 30 turns CCW, then I turned them 12½ +2 = 14½ turns CW to get to the middle.
The bias trimmers are a different situation. The SM says to turn them all the way CCW, but the originals are AFU and I failed to record the pinouts when I removed them. I don't know if I should start with a minimum resistance (0.6Ω) or a maximum resistance (98.4Ω) to get minimum bias.
Will someone please look at this circuit and give me the answer? Then I can install it (VR03&4) in the correct, conventional orientation.
Thanks - - -
The trimmers (VR01&02) for the DC offset were simple to install because they are adjusted to minimize the DC at the speaker terminals by balancing the differential inputs. The direction to be turned to increase or decrease the bias will reverse if you cross to the other side of the balance point.
I replaced the single turn pots with 25 turn bourn style pots to allow for finer adjustments. 5 turn pots would have been AOK, but 25 turn pots are easier to find. Using a spare trimmer I turned it CCW 30 times to make sure that I was at the low end (0.6Ω to 98.4Ω), and found that it takes about 2 turns to get the wiper back in contact with the element and start increasing the value. So, I went back to the trimmers installed on the PCB and gave them 30 turns CCW, then I turned them 12½ +2 = 14½ turns CW to get to the middle.
The bias trimmers are a different situation. The SM says to turn them all the way CCW, but the originals are AFU and I failed to record the pinouts when I removed them. I don't know if I should start with a minimum resistance (0.6Ω) or a maximum resistance (98.4Ω) to get minimum bias.
Will someone please look at this circuit and give me the answer? Then I can install it (VR03&4) in the correct, conventional orientation.
Thanks - - -
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ghazzer
Senior Member
Some research and a PM have indicated that pin 3 of the trimmer should be 'facing' the STV-3H diodes, with pins 1&2 connected. This gives VR03 its max value and minimum bias current when the trimmer is turned full CCW.
I continue to get confused that the circuit layout of the L/R channels on this board is often, but not always, a mirror image. I thought that I had installed the trimmers of each channel correctly, but had to reverse VR04 so that pin 3 of each is now 'facing' the diodes.
The printer died (black cartridge would not print) and my wife could not print coupons, so there was a crisis I had to resolve. Finally deduced that the print head was at fault, and ordering a replacement would take 4-5 days. It was easier to get a new printer using the same cartridges. It was on special with free shipping and it arrived the next day.
Now I can get back to my other projects.
I continue to get confused that the circuit layout of the L/R channels on this board is often, but not always, a mirror image. I thought that I had installed the trimmers of each channel correctly, but had to reverse VR04 so that pin 3 of each is now 'facing' the diodes.
The printer died (black cartridge would not print) and my wife could not print coupons, so there was a crisis I had to resolve. Finally deduced that the print head was at fault, and ordering a replacement would take 4-5 days. It was easier to get a new printer using the same cartridges. It was on special with free shipping and it arrived the next day.
Now I can get back to my other projects.
petehall347
the brandy coffee man
not long till music playing then ..
ghazzer
Senior Member
Power-up testing..... Finally
Here is a summary of what I have done:
Replaced almost everything on the 2980 & 3058 board except for the TRs in the P/S, some small ceramic caps, FETs, diodes, relays, and coils.
Components were checked for values before installation.
After install I checked for continuity between the lead and the pad before clipping the lead.
Inspected all jumpers and replaced two of them
Board washed clean and examined for solder splash.
Test point loops added to 2980 board so I can attach mini grabbers to monitor bias voltages.
0.33Ω emitter resistors temporarily replaced with 100Ω (5).
3058 boards floating, so output TRs and STV diodes NOT on heat sinks.
Cardboard taped to chassis to prevent contact with 3058 bds.
25 turn DC Offset trimmers set at mid point.
25 turn Bias trimmers set to full CCW, then 2 turns back - ~96Ω is in circuit.
DBT in place with 60 watt bulb.
This was my plan:
1st Apply power with DBT in place. Increase bulb to 135 watt and recheck. REMOVE DBT if no problems.
2nd With volume at minimum and DMM monitoring bias voltage, set DC offset to minimum. Repeat for other channel
3rd Turn bias pot 2 turns CW (8% change) and ensure that bias goes up slightly.
4th Power off and replace 100Ω emitter resistors with 0.33Ω(5) resistors. Replace mica washers & mount TRs and STV diodes to heat sink
5th Put DBT back in circuit and apply power. Remove DBT if no problems.
6th Apply power and recheck DC Offset
7th Adjust bias voltage in each channel to WHAT???? SM says 5V ±1mv, but I think I read somewhere that this is a misprint and should be 5mv ±1mv
.
I didn't get past the 1st step. The DBT came up BRITE and dimmed quickly. Bias in both channels was ~0.0mv, but I was reading 27 VOLTS at the right speaker terminals, so I shut it down PDQ.
No Smoke
No Snap, Crackle or Pop
No flashing DBT
Moved DMM #3 to the left speaker and tried again. Left channel reads 27.5 VOLTS. Safe operate relay kicked in at about 4 seconds, then off ~4 seconds later - cycles like that so I shut it down. CORRECTION: SO clicks on after ~4sec, then off PDQ. This cycle repeats in ~4 seconds.
Main Caps are reading ±41, S/B ±61.
Tried reading what S/B -18.3V at R15 (tied to wiper of VR01) but it starts climbing then resets when the safe operate relay clicks. Sometimes I can read ~280mv. Same on the right channel.
TR602/C, C613 & R608 are marked as -46V on the schematic, but reads -31V
Pin 26 & pin 27 S/B ±32V respectively, but measure ±28V.
Don't know where to go from here, but I am encouraged . . . . .
Looked
Here is a summary of what I have done:
Replaced almost everything on the 2980 & 3058 board except for the TRs in the P/S, some small ceramic caps, FETs, diodes, relays, and coils.
Components were checked for values before installation.
After install I checked for continuity between the lead and the pad before clipping the lead.
Inspected all jumpers and replaced two of them
Board washed clean and examined for solder splash.
Test point loops added to 2980 board so I can attach mini grabbers to monitor bias voltages.
0.33Ω emitter resistors temporarily replaced with 100Ω (5).
3058 boards floating, so output TRs and STV diodes NOT on heat sinks.
Cardboard taped to chassis to prevent contact with 3058 bds.
25 turn DC Offset trimmers set at mid point.
25 turn Bias trimmers set to full CCW, then 2 turns back - ~96Ω is in circuit.
DBT in place with 60 watt bulb.
This was my plan:
1st Apply power with DBT in place. Increase bulb to 135 watt and recheck. REMOVE DBT if no problems.
2nd With volume at minimum and DMM monitoring bias voltage, set DC offset to minimum. Repeat for other channel
3rd Turn bias pot 2 turns CW (8% change) and ensure that bias goes up slightly.
4th Power off and replace 100Ω emitter resistors with 0.33Ω(5) resistors. Replace mica washers & mount TRs and STV diodes to heat sink
5th Put DBT back in circuit and apply power. Remove DBT if no problems.
6th Apply power and recheck DC Offset
7th Adjust bias voltage in each channel to WHAT???? SM says 5V ±1mv, but I think I read somewhere that this is a misprint and should be 5mv ±1mv
.
I didn't get past the 1st step. The DBT came up BRITE and dimmed quickly. Bias in both channels was ~0.0mv, but I was reading 27 VOLTS at the right speaker terminals, so I shut it down PDQ.
No Smoke
No Snap, Crackle or Pop
No flashing DBT
Moved DMM #3 to the left speaker and tried again. Left channel reads 27.5 VOLTS. Safe operate relay kicked in at about 4 seconds, then off ~4 seconds later - cycles like that so I shut it down. CORRECTION: SO clicks on after ~4sec, then off PDQ. This cycle repeats in ~4 seconds.
Main Caps are reading ±41, S/B ±61.
Tried reading what S/B -18.3V at R15 (tied to wiper of VR01) but it starts climbing then resets when the safe operate relay clicks. Sometimes I can read ~280mv. Same on the right channel.
TR602/C, C613 & R608 are marked as -46V on the schematic, but reads -31V
Pin 26 & pin 27 S/B ±32V respectively, but measure ±28V.
Don't know where to go from here, but I am encouraged . . . . .
Looked
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