My first receiver restoration attempt: G-6700.
- Thread starter ghazzer
- Start date
kevzep
Its all about the Music
It's KSC2690A and they are available at Mouser and I have used these before many many times in these amplifiers....
I am sitting here looking at a bag of them right now....
The problem is the typo in my notes which I copied and Pasted into this thread to avoid this VERY problem, I have corrected this......
Sorry for the confusion guys....
Here they are at mouser.....
http://eu.mouser.com/ProductDetail/...C2690AOS/?qs=sGAEpiMZZMtdAabcSkQOl9cAgmIxTE0d
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ghazzer
Senior Member
I modified the curve tracer that DCinDC told me about. The plan called for a 6.3vac xfmr and I had a 5vac one so I adjusted the voltage divider to give about the same voltage level with the 5v as one would get with a 6.3v. I also added some banana jacks so that test leads can be easily plugged in.
With an X/Y scope attached and the test leads across a component, the scope will display a pattern that indicates the impedance of the component. much better than a simple resistance reading of a component that is still in the circuit.
If you check B-E on a transistor it might display a "┐", and an E-B check would get a "└", mirrored and flipped.
So far I have found a lifted track at TR08/B, so there was no connection to TR16/B. And there is the botched tracks under the OP TRs - hope I don't have to rebuild that board.
The track repair that I tried with the copper foiling tape did not hold up for more than one solder, so I am looking for a better adhesive that will withstand the ~500°F from soldering.
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With an X/Y scope attached and the test leads across a component, the scope will display a pattern that indicates the impedance of the component. much better than a simple resistance reading of a component that is still in the circuit.
If you check B-E on a transistor it might display a "┐", and an E-B check would get a "└", mirrored and flipped.
So far I have found a lifted track at TR08/B, so there was no connection to TR16/B. And there is the botched tracks under the OP TRs - hope I don't have to rebuild that board.
The track repair that I tried with the copper foiling tape did not hold up for more than one solder, so I am looking for a better adhesive that will withstand the ~500°F from soldering.
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I'm with DC on this one. Point to point the traces, or just use the original board pattern to make a new one. The one I did was point to point, however with time and patience, copper clad boards and etchant you could really come up with something more 'factory'
-Lee
-Lee
ghazzer
Senior Member
My order of trimpots came in. The flat ones are just too flimsy. I got 10, and 7 of them had ranges like 7-8Ω up to 85-86Ω, and all this in only about 300° of arc. I decided to use the 3296 style, 25 turn pots instead.
I turned each of the originals full CCW on the board, then checked each one with an ohm meter when I pulled it out and recorded which side had the lowest reading. All of the 3296 pots were set for ~1Ω befor I installed them.
I still have to re-read the Andreslober thread to see if there is a safe way to power up the receiver with the OP TRs removed. I ordered a set of the 100Ω 5W CC resistors, but they are backordered and have not even been shipped yet.
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I turned each of the originals full CCW on the board, then checked each one with an ohm meter when I pulled it out and recorded which side had the lowest reading. All of the 3296 pots were set for ~1Ω befor I installed them.
I still have to re-read the Andreslober thread to see if there is a safe way to power up the receiver with the OP TRs removed. I ordered a set of the 100Ω 5W CC resistors, but they are backordered and have not even been shipped yet.
.
ghazzer
Senior Member
Here is a summary of my findings so far:
OP TRs are shorted in Rt Ch.
Lifted & missing tracks on OP TR board
One open/lifted track at TR04/c to TR08/b
R57 (L) reads 177Ω and R58(R) reads 1.2KΩ (near TR19&20/b). Should be 1.2K, so why is the "good" channel reading odd? I pulled both resistors and they both read 1.2K. Other readings around TR19 seemed funky so I pulled 19 &20. They checked good, and the same as TR07&08 (all 2SA939s).Looking at the schematic I finally got to the STV-3H diode and remembered that it was removed when I cleared the 3058 board to try & repair the tracks. Clipped the leads of the STV-3H to the wires coming off the driver board and the associated readings now compare OK to the Left channel - I been chasing wild geese!
One of the four 100Ω trimmers that I replaced is cracked and reads 25-30MΩ. I thought that they all looked good when checked in circuit, but I replaced them because kevzep said that was the first thing I should do. And, I only checked for the minimum reading when I pulled them because I turned them all CCW before removal. This means that I don't know which position this one was in. It could be the major fault that caused everything else.
My next action will be to rebuild the 3058 board for the right channel and install the OP TRs that I got from China. Fix all of the above that I can, and bring it up on a DBT.
I have used the "component tester" suggested by DCinDC and gotten some L/R readings that do not compare. After the fiasco with R57/58, I’m gonna wait until I have the replacement OP TRs wired in and recheck those readings.
@#@#@#@#@#@#@#
I need to replace some of the short wiring between the driver board and the board where the OP TRs are mounted. Can someone tell me the correct terminology for the pin clips on the end of these jumpers? The holes in the PCB are about 0.07", so tinned wire leads are too small.
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OP TRs are shorted in Rt Ch.
Lifted & missing tracks on OP TR board
One open/lifted track at TR04/c to TR08/b
R57 (L) reads 177Ω and R58(R) reads 1.2KΩ (near TR19&20/b). Should be 1.2K, so why is the "good" channel reading odd? I pulled both resistors and they both read 1.2K. Other readings around TR19 seemed funky so I pulled 19 &20. They checked good, and the same as TR07&08 (all 2SA939s).Looking at the schematic I finally got to the STV-3H diode and remembered that it was removed when I cleared the 3058 board to try & repair the tracks. Clipped the leads of the STV-3H to the wires coming off the driver board and the associated readings now compare OK to the Left channel - I been chasing wild geese!
One of the four 100Ω trimmers that I replaced is cracked and reads 25-30MΩ. I thought that they all looked good when checked in circuit, but I replaced them because kevzep said that was the first thing I should do. And, I only checked for the minimum reading when I pulled them because I turned them all CCW before removal. This means that I don't know which position this one was in. It could be the major fault that caused everything else.
My next action will be to rebuild the 3058 board for the right channel and install the OP TRs that I got from China. Fix all of the above that I can, and bring it up on a DBT.
I have used the "component tester" suggested by DCinDC and gotten some L/R readings that do not compare. After the fiasco with R57/58, I’m gonna wait until I have the replacement OP TRs wired in and recheck those readings.
@#@#@#@#@#@#@#
I need to replace some of the short wiring between the driver board and the board where the OP TRs are mounted. Can someone tell me the correct terminology for the pin clips on the end of these jumpers? The holes in the PCB are about 0.07", so tinned wire leads are too small.
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"One of the four 100Ω trimmers that I replaced is cracked and reads 25-30MΩ. I thought that they all looked good when checked in circuit, but I replaced them because kevzep said that was the first thing I should do."
A bad trim pot will cause instant mayhem in this circuit :yes:
Reading resistors in place often is a dicey proposition depending on their interaction with other elements of the circuit they are associated with.
-Lee
A bad trim pot will cause instant mayhem in this circuit :yes:
Reading resistors in place often is a dicey proposition depending on their interaction with other elements of the circuit they are associated with.
-Lee
ghazzer
Senior Member
Yes. That is why I started with the "easy" check, looking for a shorted or open component. That is how I found the open track at the base of TR08. My next phase was to check everything with the curve tracer, and it is also very dependant on parallel circuits when checking across some components. You can also use the curve tracer to check between ground and each solder joint.Overundr1;6301019 Reading resistors in place often is a dicey proposition depending on their interaction with other elements of the circuit they are associated with. -Lee[/QUOTE said:
Do you have any suggestion as to the correct nomenclature for the pins that are used on the ends of the short jumpers, or where I can find some? Doubling the ends of the wire might work, but I'd like a more lasting solution if I can find one.
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ghazzer
Senior Member
Which is correct?????
Sansui's schematic for the OP TR boards shows PNP (upper) and NPN (lower) on each board. The reference designators of 601 and 604 don't agree with the key showing 601 2SC2581 (NPN) and 602 2SA1106 (PNP).
The right channel board in this G-6700 had the reverse order of the reference designators, but I don't know if that was correct, or what caused them to fail.
Can anyone tell me the correct order for these transistors on each board?
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Sansui's schematic for the OP TR boards shows PNP (upper) and NPN (lower) on each board. The reference designators of 601 and 604 don't agree with the key showing 601 2SC2581 (NPN) and 602 2SA1106 (PNP).
The right channel board in this G-6700 had the reverse order of the reference designators, but I don't know if that was correct, or what caused them to fail.
Can anyone tell me the correct order for these transistors on each board?
.
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kevzep
Its all about the Music
The diagrams are correct but the designations are wrong......
Just follow the Output transistors back to the drivers.....NPN drives NPN and PNP drives PNP........
TR604 is a NPN (2SC2581) transistor, and TR601 is the PNP (2SA1106)
This is a hands on board. You will need to follow the path from each predriver (npn/pnp) to its corresponding output transistor. Watch the output configuration, I am pretty sure they are b-c-e devices. The emitters tie together which means you have to have a trace between the two, or on the last one I rebuilt a jumper wire to the emitter resistor on the right hand output crossing over the other two leads. Get a picture up before you apply power for us to take a look.
ghazzer
Senior Member
Yeah, I just double checked my work, and I did in fact install the replacement OP TRs in the same orientation as the last repair: bassackwards! How long would they have lasted after power was applied? The 7A fuse was also blown, so the protection circuity was not designed for that scenario.
I hope that what is left of the tracks on this board can withstand one more round of soldering. I will post some pics as I rebuild.
I still haven't placed the order for all the replacement TRs and electrolytic caps, and will probably wait until I return after Christmas. The new 0.33Ω,5W emmitter resisters are in the same boat, so I'll use the 0.39Ω,5W ones from the last repair, for the time being. It will be nice to get it all wired up and checked out with DCinDC's curve tracer before I place the order.
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I hope that what is left of the tracks on this board can withstand one more round of soldering. I will post some pics as I rebuild.
I still haven't placed the order for all the replacement TRs and electrolytic caps, and will probably wait until I return after Christmas. The new 0.33Ω,5W emmitter resisters are in the same boat, so I'll use the 0.39Ω,5W ones from the last repair, for the time being. It will be nice to get it all wired up and checked out with DCinDC's curve tracer before I place the order.
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ghazzer
Senior Member
Thank You, Thank You very much. I have removed the TRs, cleaned up the board, and put down new track with the copper foiling tape. The adhesive will not survive the soldering, but it should stay in place long enuff to establish a solder bond. This 40+ year old PCB just "can't take the heat".
'Going out to supper right now and will crank up the iron when we get back. I may come calling if falls to pieces - - -
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'Going out to supper right now and will crank up the iron when we get back. I may come calling if falls to pieces - - -
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ghazzer
Senior Member
I guess that I should hang this up until after the holidays - maybe I'll make fewer dumb mistakes.
The left & right channels are mirror images on the driver board, but not on the schematic. I convinced myself that both of the F-3058 boards should be laid out the same just by looking at the schematics, so I removed the OP TRs I had recently installed, and reversed them. When I positioned the 3058 board next to the driver board to re-connect the jumpers I realized my mistake. Now I have to remove the TRs, again, and un-reverse them.
I asked the owner of a local H/W store about hi temp adhesives that could be used to attach copper foiling tape to a PCB and withstand soldering temperatures. He suggested a hi temp flue tape that is metallic, but he is out of stock at the moment. I'll try it when I get back.
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The left & right channels are mirror images on the driver board, but not on the schematic. I convinced myself that both of the F-3058 boards should be laid out the same just by looking at the schematics, so I removed the OP TRs I had recently installed, and reversed them. When I positioned the 3058 board next to the driver board to re-connect the jumpers I realized my mistake. Now I have to remove the TRs, again, and un-reverse them.
I asked the owner of a local H/W store about hi temp adhesives that could be used to attach copper foiling tape to a PCB and withstand soldering temperatures. He suggested a hi temp flue tape that is metallic, but he is out of stock at the moment. I'll try it when I get back.
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ghazzer
Senior Member
I finally got the right channel F-3058 board rebuilt – correctly I hope. I used some connector pins from Ohighway’s parts bins to help replace a couple of jumpers that were mangled or damaged. Pictures taken during disassembly helped me get jumpers to the right places.
DCinDC’s component tester widget was used to do an in circuit check of the components in the driver section, comparing left channel to right channel. Most everything checked OK after replacing the trimmer pots and the output TRs, repairing what I think was a broken track, and rewiring the 3058 board. Several of the components near R06 & R08 were generating a sloped ellipse (mostly capitance) in the right channel and almost collapsed ellipse (mostly restive) in the left channel near R05 & R07. This was tracked back to a sticky/dirty subsonic filter button that was staying “on” in the right ch, and resolved with a shot of QD contact cleaner.
Now I am going to go back and re-read Anderslober’s thread about repairing this same F-2980 board in a G-7500 project. I want to make sure that I observe all the cautions and suggestions that Overundr1 and Kevzep contributed.
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DCinDC’s component tester widget was used to do an in circuit check of the components in the driver section, comparing left channel to right channel. Most everything checked OK after replacing the trimmer pots and the output TRs, repairing what I think was a broken track, and rewiring the 3058 board. Several of the components near R06 & R08 were generating a sloped ellipse (mostly capitance) in the right channel and almost collapsed ellipse (mostly restive) in the left channel near R05 & R07. This was tracked back to a sticky/dirty subsonic filter button that was staying “on” in the right ch, and resolved with a shot of QD contact cleaner.
Now I am going to go back and re-read Anderslober’s thread about repairing this same F-2980 board in a G-7500 project. I want to make sure that I observe all the cautions and suggestions that Overundr1 and Kevzep contributed.
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ghazzer
Senior Member
Well, I guess that I am over the first hurdle of powering it up.
The DBT went bright, then quickly to dim, with a 60 watt bulb. After what seemed like two eternities the green light came on for Safety Operate, plus some panel lights. The digital display came up when I switched to FM and AM, but there is no sound at all in the headphones, Nada!
The main caps are putting out ±41VDC but the schematic says that should be ±61VDC. The inputs to the DC adjust trim pots is -17.9VDC vs the -18.3 of the schematic. The other side of the FETs is reading +17.9VDC vs +18.3.
The voltage at the junction of the two emitter resistors in the Left channel is -1.86VDC and the right channel is +2.24VDC. I would have thought that these two would have been the same. The input lines from the tone board are 0.0VDC for the left and -1.1mvdc for the right.
I bought 2 kits for a 1Khz tone source, so I guess that I should slap them together and start tracing the signal from the front end.
At least there was no smoke or loud noises - - -
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The DBT went bright, then quickly to dim, with a 60 watt bulb. After what seemed like two eternities the green light came on for Safety Operate, plus some panel lights. The digital display came up when I switched to FM and AM, but there is no sound at all in the headphones, Nada!
The main caps are putting out ±41VDC but the schematic says that should be ±61VDC. The inputs to the DC adjust trim pots is -17.9VDC vs the -18.3 of the schematic. The other side of the FETs is reading +17.9VDC vs +18.3.
The voltage at the junction of the two emitter resistors in the Left channel is -1.86VDC and the right channel is +2.24VDC. I would have thought that these two would have been the same. The input lines from the tone board are 0.0VDC for the left and -1.1mvdc for the right.
I bought 2 kits for a 1Khz tone source, so I guess that I should slap them together and start tracing the signal from the front end.
At least there was no smoke or loud noises - - -
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