Kenwood 700M repair project
- Thread starter p_vander
- Start date
redcoates7
still learning...
not at all, just love hearing about the things a really careful restorer goes through a piece of gear to make sure it's going to perform up to spec again!
doubt i can ever afford one of those, but I would love to stumble across one of those some day. I am going to steal an idea that I got from admiring that amp. I love the way they have it setup on the vintage knob pic, built into the wall like that. As I am redoing my garage for a listening area, I am going to try and implement that into the room design - a wall with just enough room to squeeze in behind for access to wiring etc, plus maybe a fan.
I may never get to own that series but I can get it to look as much like it as possible anyway.
I may never get to own that series but I can get it to look as much like it as possible anyway.
p_vander
Member
I only got 3 of the transistors in today, because of one issue...
I was at the computer store today buying heatsink paste, and the guy behind the counter suggests I buy the OCZ freeze paste because it's better than the generic silicon stuff I was buying and only 50 cents more. I have a look at the packages, I can't see any information on the volume of the OCZ stuff, but the tubes are about the same size, so I decide to buy it.
When I get it home, I find out that it has only about 1/3 of what the generic stuff had (3g as opposed to 10g). The amount is written on the back of the label of the tube, which was positioned inside the blister pack in such a way that it would be VERY hard to read it. Also, the paste came in a syringe type tube. I lined up the plunger with where it would be positioned for the syringe to fit inside the blister pack and drew a line across the plunger where it meets the body of the syringe. I pulled it out to find that the line was HALFWAY down the plunger.
Needless to say, I am somewhat annoyed. It's mostly due to not getting my transistors in tonight, but also, to me, selling half-filled tubes with hard to read information on how much they contain seems a little deceptive.
Sorry folks... just had to rant :grumpy:
I'm going back tomorrow and buying the generic stuff. Even if the OCZ paste does indeed cool better, some transistors being slightly cooler than others is not going to really make a difference anyway.
I was at the computer store today buying heatsink paste, and the guy behind the counter suggests I buy the OCZ freeze paste because it's better than the generic silicon stuff I was buying and only 50 cents more. I have a look at the packages, I can't see any information on the volume of the OCZ stuff, but the tubes are about the same size, so I decide to buy it.
When I get it home, I find out that it has only about 1/3 of what the generic stuff had (3g as opposed to 10g). The amount is written on the back of the label of the tube, which was positioned inside the blister pack in such a way that it would be VERY hard to read it. Also, the paste came in a syringe type tube. I lined up the plunger with where it would be positioned for the syringe to fit inside the blister pack and drew a line across the plunger where it meets the body of the syringe. I pulled it out to find that the line was HALFWAY down the plunger.
Needless to say, I am somewhat annoyed. It's mostly due to not getting my transistors in tonight, but also, to me, selling half-filled tubes with hard to read information on how much they contain seems a little deceptive.
Sorry folks... just had to rant :grumpy:
I'm going back tomorrow and buying the generic stuff. Even if the OCZ paste does indeed cool better, some transistors being slightly cooler than others is not going to really make a difference anyway.
p_vander
Member
The transistors are now in, it definitely cleans up the look of the heatsinks to have shiny new transistors in there. :thmbsp:
I managed to find some bulbs for the front that are close to original spec, but not quite. The originals were 8V 0.3A, I found some 7.5V 0.22A that fit. It looks like these should work as a direct replacement, since the bulbs are connected to either the 5V or 7.5V leads off the power transformer, depending on the dimmer switch position.
I managed to find some bulbs for the front that are close to original spec, but not quite. The originals were 8V 0.3A, I found some 7.5V 0.22A that fit. It looks like these should work as a direct replacement, since the bulbs are connected to either the 5V or 7.5V leads off the power transformer, depending on the dimmer switch position.
p_vander
Member
I'm waiting for my service manual to arrive so that I can verify that everything is correct before I apply power. It arrived at my parents' place on the west coast today and they're forwarding it to me by regular mail, so I'm going to have to go through several days of torment staring at my 700M that I want to test but can't. :tears:
I'll let you know how the bulbs as soon as I test it. The tint doesn't matter, there is a blue filter at the top of each VU meter. I won't be able to tell you if there is a difference in brightness since I had to replace all the bulbs in my 700M. I can't wait to bask in the blue glow of that front panel, though...
I'll let you know how the bulbs as soon as I test it. The tint doesn't matter, there is a blue filter at the top of each VU meter. I won't be able to tell you if there is a difference in brightness since I had to replace all the bulbs in my 700M. I can't wait to bask in the blue glow of that front panel, though...
cchean
Super Member
Hey p_Vander,
Very interesting thread. As a recent 700m owner, this thread will help me a lot as I am sure will help a lot of other people...
By the way, did you get the chance to look at the link I posted in this thread? That guy did an amazing restoration job too.
I hope you could help me out with something. I just got a 700m and my right VU meter is kinda "lazy", it moves about 1/16 of an inch when it's set at -20db, at other settings it practically doesn't move. Are there any components between the meters and the signal source that are likely to degrade or cause it to loose its movement? Any input will be greatly appreciated. Thanks.
Very interesting thread. As a recent 700m owner, this thread will help me a lot as I am sure will help a lot of other people...
By the way, did you get the chance to look at the link I posted in this thread? That guy did an amazing restoration job too.
I hope you could help me out with something. I just got a 700m and my right VU meter is kinda "lazy", it moves about 1/16 of an inch when it's set at -20db, at other settings it practically doesn't move. Are there any components between the meters and the signal source that are likely to degrade or cause it to loose its movement? Any input will be greatly appreciated. Thanks.
p_vander
Member
cchean,
I've been looking at your 700M thread... It definitely gives me inspiration to get this project done.
I'd seen that link you posted before, when I was searching for info on the Kenwood 700M. That is an absolutely amazing restoration job. :thmbsp:
There is a driver board for the meters directly behind the buttons on the front panel. I can see a couple transistors, some caps and resistors, as well as a couple pots. I imagine that there is a small-signal transistor amp for each meter and the buttons control the resistors used to set the gain. The pot may have something to to with fine tuning of the gain. I'm not sure on this, but I should be able to tell better when I get a schematic.
The parts most likely to give you trouble in that circuit would be the electrolytic caps or the pots. It could also be the connectors on the board as well. They're silver and it's possible that they've oxidised and you're just getting a bad connection.
I've been looking at your 700M thread... It definitely gives me inspiration to get this project done.
I'd seen that link you posted before, when I was searching for info on the Kenwood 700M. That is an absolutely amazing restoration job. :thmbsp:
There is a driver board for the meters directly behind the buttons on the front panel. I can see a couple transistors, some caps and resistors, as well as a couple pots. I imagine that there is a small-signal transistor amp for each meter and the buttons control the resistors used to set the gain. The pot may have something to to with fine tuning of the gain. I'm not sure on this, but I should be able to tell better when I get a schematic.
The parts most likely to give you trouble in that circuit would be the electrolytic caps or the pots. It could also be the connectors on the board as well. They're silver and it's possible that they've oxidised and you're just getting a bad connection.
Doesn't matter much...these are simply the V/I limiters, designed to reduce the drive to the driver & output stage when the amp is pushed too hard. Under normal conditions they just sit there.
Note that Q5 (on the new style boards, such as you have...the X07-1310) has the emitter and collector reversed. This should be corrected on your board.
Note that Q5 (on the new style boards, such as you have...the X07-1310) has the emitter and collector reversed. This should be corrected on your board.
Attachments
Also forgot to mention that, if you're doing a full recapping, one of the 10µf caps on the meter driver board is marked backwards on the PC board silkscreen. Offhand I forget which one, but since the meters work as shipped, just make sure you reinstall the same way the old ones came out.
p_vander
Member
Thanks EW... That should help me avoid some potentially nasty surprises. I didn't have a chance to look at the schematic closely, but if those transistors don't come into play until the amp reaches its limits, I'd rather not replace them unless I need to.
I test fired it today and the bulb on my dim-bulb tester shone bright as day.:tears:
I'll need to go over the wiring and check with the schematic again. I did notice that the positions of the yellow and red wire pairs are different inside the amp than they are on the schematic. They yellow wires in my amp are connected to the unswitched outlets and the red ones are connected to the 4 ohm resistor. When I traced the lines on the schematic, it said that the red is to be connected to the unswitched side and the yellow is to be connected to the resistor. From photos I have seen of other 700M units, they seem to be wired the same as mine, with the red wires coming off the resistor.:headscrat
I am using a 100W bulb in my tester. Is it possible that I need a lower wattage bulb in series with the amp to allow the protection relays to trip?
I test fired it today and the bulb on my dim-bulb tester shone bright as day.:tears:
I'll need to go over the wiring and check with the schematic again. I did notice that the positions of the yellow and red wire pairs are different inside the amp than they are on the schematic. They yellow wires in my amp are connected to the unswitched outlets and the red ones are connected to the 4 ohm resistor. When I traced the lines on the schematic, it said that the red is to be connected to the unswitched side and the yellow is to be connected to the resistor. From photos I have seen of other 700M units, they seem to be wired the same as mine, with the red wires coming off the resistor.:headscrat
I am using a 100W bulb in my tester. Is it possible that I need a lower wattage bulb in series with the amp to allow the protection relays to trip?
A lower wattage bulb will allow less current to flow. A higher wattage bulb will allow more current to flow. Stick with a 100W bulb. And until you get this panel wiring figured out, remove the output transistors and driver boards.
The rear panel wiring is confusing, and to make matters worse, there's about 5 or 6 different revisions, depending on the transformer and the country it was intended to be sold in. But, the most common setup is one that I have documented.
You mentioned something about a service bulletin. I'd like to see that.
The rear panel wiring is confusing, and to make matters worse, there's about 5 or 6 different revisions, depending on the transformer and the country it was intended to be sold in. But, the most common setup is one that I have documented.
You mentioned something about a service bulletin. I'd like to see that.
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Meant to say that...look at the pic in Post #34. Qe5 has likely been installed for many years improperly, and can no longer be trusted. If you want the current limit to function properly, replace Qe5 at a minimum (and reinstall according to the second pic), and preferably replace all four (Qe5~Qe8), especially since the amp has been blown.
p_vander
Member
That diagram and those pictures are definitely helpful 
I don't see the yellow wire for the low side of the blue/yellow pair on the primary inside my amp. I don't see it coming out of the bundle of wires that go to the transformer - there are only red, blue and white. I'll have to check further down the line to to see where it might be or what is connected to the low side of the primary there.
My free time these days is less, so I don't have quite as much time to devote to this project.
...I also leads to things like rushed posting before thinking things through and remembering that a higher wattage bulb would allow more current to flow without burning out. Remember kids: Think twice, post once :stupid:
I don't see the yellow wire for the low side of the blue/yellow pair on the primary inside my amp. I don't see it coming out of the bundle of wires that go to the transformer - there are only red, blue and white. I'll have to check further down the line to to see where it might be or what is connected to the low side of the primary there.
My free time these days is less, so I don't have quite as much time to devote to this project.
...I also leads to things like rushed posting before thinking things through and remembering that a higher wattage bulb would allow more current to flow without burning out. Remember kids: Think twice, post once :stupid: