Sansui G-7500 Fried Resistors F2980 Board

[Young46]

[QUOTE="kevzep, post: 11725848,
But for an experienced tech, I agree they are not that difficult to fix, given the difficulty of helping someone over the internet, and the level at which you need to be to repair one of these, well, that's why we've ended up here...
I also do not have the time to help, I got a little but involved but its hard when you don't really know how much the person you are helping does know...[/QUOTE]
So if one is not a professional tech who has masters degrees in electrical engineering and had a fully equipped shop with all the latest test equipment, don’t bother asking for help on this forum? But why would such person be asking for help in the first place? It’s the novices like myself who need the help. I don’t begrudge you for not wanting or having the time to help. But wouldn’t it be best to just not get engaged in the conversation at all? I thought that I explained up front my level of expertise. Right now I get the message that if you are not an expert in electrical/electronics, don’t bother asking for help with your equipment that has issues. Am I wrong?

 

[kevzep]

But for an experienced tech, I agree they are not that difficult to fix, given the difficulty of helping someone over the internet, and the level at which you need to be to repair one of these, well, that's why we've ended up here...
I also do not have the time to help, I got a little but involved but its hard when you don't really know how much the person you are helping does know...
So if one is not a professional tech who has masters degrees in electrical engineering and had a fully equipped shop with all the latest test equipment, don’t bother asking for help on this forum? But why would such person be asking for help in the first place? It’s the novices like myself who need the help. I don’t begrudge you for not wanting or having the time to help. But wouldn’t it be best to just not get engaged in the conversation at all? I thought that I explained up front my level of expertise. Right now I get the message that if you are not an expert in electrical/electronics, don’t bother asking for help with your equipment that has issues. Am I wrong?

You need to step back and read the posts properly, I never at any time said or suggested "if one is not a professional tech who has masters degrees in electrical engineering and had a fully equipped shop with all the latest test equipment, don’t bother asking for help on this forum?"
Why are you being so antagonistic? I help a lot of people, not just in the Sansui forum, Pioneer, McIntosh, so seriously what are you talking about. All in my own time, and selflessly educating people helping people as a lot of other members do here.
I do not always have the time to spend helping every person that asks for it, I have a life, a full time job, and a sideline business.

You are getting completely the wrong message from these posts.
As I said, go and search how many G5700/6700/7700 threads go cold very quickly because of the nature of these amplifiers.

Again, I repeat, you chose a very difficult project with the G7500, they are not in the least bit easy to repair, how many other ways do you want me to explain it? As you are a novice with little experience, trying to repair something like this, is very very difficult and sadly for you, in the case of this G7500, you require some level of electronics understanding, which clearly after all this, you do not have. Sure, if it was an AU999 or something like that, we can guide you through and tell you which parts to replace and if you make a mistake or misunderstand something the amplifier will not catastrophically fail, but with the G7500 amplifier, its not as simple as that, this has been explained to you and yet you come back here complaining....

You had most of the experts in this forum replying to your thread giving their own free time to help you, including me, then you come back here and start throwing these statements around complaining you weren't getting the same sort of help you get in the Pioneer forum restoring and working on much simpler and forgiving amplifiers as the Pioneers are.

I suggest you step back and get some perspective on this and try and learn something from it.

By the way, the most modern piece of test equipment I own, is 25 years old!!

 

[Hipocrates]

Am I wrong?

Yes.
In this particular case, will be hard to get help... Specifically in Sansuis with F2980 boards.
Same goes for example on Pioneer SA-9900 or Marantz 1250 on the other forums.
That been said, with another units AU's from the 70's, X0X0 or G-X000's, you will get more help, just like the Pioneer forum with SX receivers or Marantz 22XX on the marantz forum.
What I'm trying to explain you (with my limited english) is that, they are some units there that would be very hard to get someone to remotely fix your amp no matter what forum you are, and your unit is one of those.

And that doesn't mean that people do not want to help you, or that some techs feels like food are being taken from their tables, as you distastefully said.

BTW, Self entitlement won't get you more help.

 

[Young46]

You need to step back and read the posts properly, I never at any time said or suggested "if one is not a professional tech who has masters degrees in electrical engineering and had a fully equipped shop with all the latest test equipment, don’t bother asking for help on this forum?"
Why are you being so antagonistic? I help a lot of people, not just in the Sansui forum, Pioneer, McIntosh, so seriously what are you talking about. All in my own time, and selflessly educating people helping people as a lot of other members do here.
I do not always have the time to spend helping every person that asks for it, I have a life, a full time job, and a sideline business.

You are getting completely the wrong message from these posts.
As I said, go and search how many G5700/6700/7700 threads go cold very quickly because of the nature of these amplifiers.

Again, I repeat, you chose a very difficult project with the G7500, they are not in the least bit easy to repair, how many other ways do you want me to explain it? As you are a novice with little experience, trying to repair something like this, is very very difficult and sadly for you, in the case of this G7500, you require some level of electronics understanding, which clearly after all this, you do not have. Sure, if it was an AU999 or something like that, we can guide you through and tell you which parts to replace and if you make a mistake or misunderstand something the amplifier will not catastrophically fail, but with the G7500 amplifier, its not as simple as that, this has been explained to you and yet you come back here complaining....

You had most of the experts in this forum replying to your thread giving their own free time to help you, including me, then you come back here and start throwing these statements around complaining you weren't getting the same sort of help you get in the Pioneer forum restoring and working on much simpler and forgiving amplifiers as the Pioneers are.

I suggest you step back and get some perspective on this and try and learn something from it.

By the way, the most modern piece of test equipment I own, is 25 years old!!

I am not trying to be antagonistic. I said I didn’t begrudge you (or anybody) for not wanting or having the time to help. I understand you guys are busy, have lives and jobs. I tried to express my thanks in every post. Apparently I didn’t do such a good job of saying it.

Perhaps it’s best to not dig myself into a deeper hole by trying to explain anything else from my perspective. It’s become apparent that I have taken things out of context. I apologize for that.

I appreciate everyone’s time and as I said, it’s precious.

Please, everyone, accept my sincere apologies.

 

[tarior]

As much as it would be helpful to do, most of us working techs don't have the time and patience to walk a novice through the repair of something like Sansui G amp section. I'm always happy to give some pointers, and maybe a nudge for someone who is almost there.
I've fixed a couple of G-7000, 7500 and a 7700. All of them took out the outputs, emitter resistors, bias resistors, drivers, and sometimes a few other resistors and whatnot. Every one, the only thing I could trace the failure back to was the trimmers going open (only takes a millisecond), or maybe shorting a speaker lead at full power.

Here are a few tips:
Be methodical. If you don't have the electronics understanding necessary to be able to see a problem, and then look at the schematic and deduce the basic problem area, then you will have to check every single part very carefully. When in doubt, chuck it.

Specific to the G7xxx amps.
Fix every cracked solder joint on the amp/PS board.
Replace the bias trimmers. It's not optional.
DO NOT EVER buy semiconductors on ebay. You can buy genuine article SanKen outputs and matching drivers from Digi-Key. Don't use anything else.
Check your power supply voltages too.
If there are any VD-1212/MV12 diodes, replace 'em.
Just replace the emitter resistors with some new ones from Vishay.

 

[kevzep]

As much as it would be helpful to do, most of us working techs don't have the time and patience to walk a novice through the repair of something like Sansui G amp section. I'm always happy to give some pointers, and maybe a nudge for someone who is almost there.
I've fixed a couple of G-7000, 7500 and a 7700. All of them took out the outputs, emitter resistors, bias resistors, drivers, and sometimes a few other resistors and whatnot. Every one, the only thing I could trace the failure back to was the trimmers going open (only takes a millisecond), or maybe shorting a speaker lead at full power.

Here are a few tips:
Be methodical. If you don't have the electronics understanding necessary to be able to see a problem, and then look at the schematic and deduce the basic problem area, then you will have to check every single part very carefully. When in doubt, chuck it.

Specific to the G7xxx amps.
Fix every cracked solder joint on the amp/PS board.
Replace the bias trimmers. It's not optional.
DO NOT EVER buy semiconductors on ebay. You can buy genuine article SanKen outputs and matching drivers from Digi-Key. Don't use anything else.
Check your power supply voltages too.
If there are any VD-1212/MV12 diodes, replace 'em.
Just replace the emitter resistors with some new ones from Vishay.

I concur, the cost of those bias trimmers going intermittent for a nanosecond is horrendous....

Everything else is spot on too...

Good advice...

 

[Young46]

As much as it would be helpful to do, most of us working techs don't have the time and patience to walk a novice through the repair of something like Sansui G amp section. I'm always happy to give some pointers, and maybe a nudge for someone who is almost there.
I've fixed a couple of G-7000, 7500 and a 7700. All of them took out the outputs, emitter resistors, bias resistors, drivers, and sometimes a few other resistors and whatnot. Every one, the only thing I could trace the failure back to was the trimmers going open (only takes a millisecond), or maybe shorting a speaker lead at full power.

Here are a few tips:
Be methodical. If you don't have the electronics understanding necessary to be able to see a problem, and then look at the schematic and deduce the basic problem area, then you will have to check every single part very carefully. When in doubt, chuck it.

Specific to the G7xxx amps.
Fix every cracked solder joint on the amp/PS board.
Replace the bias trimmers. It's not optional.
DO NOT EVER buy semiconductors on ebay. You can buy genuine article SanKen outputs and matching drivers from Digi-Key. Don't use anything else.
Check your power supply voltages too.
If there are any VD-1212/MV12 diodes, replace 'em.
Just replace the emitter resistors with some new ones from Vishay.

Thank you! I appreciate your comments and tips. It’s precisely all I can ask for. I know that.

I always buy from reliable sources, mouser, digikey, parts express, and a local electronics warehouse in Houston. I appreciate the tip just the same. I did not know that the genuine Sanken outputs were available from digikey though.

If I may ask a question, regarding the trimmers. I’ve replaced them. All four. I purchased the Bourne’s, 25 or 30 turns (exact number escapes me right now) but how do you tell if they are at full cw, or full ccw? They turn to infinity either way.

Thanks again!

 

[kevzep]

I am not trying to be antagonistic. I said I didn’t begrudge you (or anybody) for not wanting or having the time to help. I understand you guys are busy, have lives and jobs. I tried to express my thanks in every post. Apparently I didn’t do such a good job of saying it.

Perhaps it’s best to not dig myself into a deeper hole by trying to explain anything else from my perspective. It’s become apparent that I have taken things out of context. I apologize for that.

I appreciate everyone’s time and as I said, it’s precious.

Please, everyone, accept my sincere apologies.

Its nothing to do with not wanting, its the interaction, sometimes people have a different thought process, a different method, mix this with remotely advising, it can get difficult.

If you came back with something tomorrow, we would all try to help again, as long as the attitude is on key. When progress is being made, the help continues. I felt with my participation that I may have been confusing the advice from ghazzer, so to minimise confusion, one of us steps out....As ghazzer seemed to have more time, it was his rodeo for a while...

Its not a big deal....you might want to talk to rcs16, he has rebuilt one of these G7500's using a different power-amp, he may have some ideas....

 

[kevzep]

but how do you tell if they are at full cw, or full ccw? They turn to infinity either way.

If you keep turning anti-clockwise for example, eventually you will hear a "clicking" sound coming from the trimmer, this indicates max (clockwise) or min (anticlockwise)......
You can also use a DMM and measure the Ω....

 

[Young46]

If you keep turning anti-clockwise for example, eventually you will hear a "clicking" sound coming from the trimmer, this indicates max (clockwise) or min (anticlockwise)......
You can also use a DMM and measure the Ω....

Thanks

 

[tarior]

I always use single turn trimmers for bias. For some of the touchier units, I'll use 25 turn Bourns for the DC offset. The bias should never be so twitchy that it won't dial in and hold with a single turn trimmer.

 

[kevzep]

I always use single turn trimmers for bias. For some of the touchier units, I'll use 25 turn Bourns for the DC offset. The bias should never be so twitchy that it won't dial in and hold with a single turn trimmer.

Snap!! Same, otherwise you're winding winding winding winding........I like 10-15 turns for DC offset, but it really does depend on the actual amplifier and how it behaves, some of these Sansui DC designs are a bit touchy for offset.....

 

[Young46]

Snap!! Same, otherwise you're winding winding winding winding........I like 10-15 turns for DC offset, but it really does depend on the actual amplifier and how it behaves, some of these Sansui DC designs are a bit touchy for offset.....

Thanks again, this is good information. One of the first things I asked for was a complete parts list (if one was available) for this board. Perhaps it fell through the cracks. Even if all the parts are not going to be replaced it is beneficial to know the correct part, or its replacement/equivalent for the ones that will be. For example, I know what a trimmer is but there are hundreds of them and I don't know if any 100 ohm will work or not. Same with caps and transistors. I, as well as many others have to rely on the expertise of you who have work successfully on these receivers.

I am attaching the SM sheet that addresses driver board adjustments for the G7500. In my post #39 I gave some readings that I obtained for bias current. In your response #40 you kinda freaked out (please don't take this out of context, I freak out all the time) over the readings and how I got them. Perhaps this sheet will explain why and how I got them.

Thanks again to you and tarior for the advice and response.

 

[tarior]

Myself, I don't have parts lists for anything. I'm just not quite that OCD, I guess.

 

[petehall347]

Thanks again, this is good information. One of the first things I asked for was a complete parts list (if one was available) for this board. Perhaps it fell through the cracks. Even if all the parts are not going to be replaced it is beneficial to know the correct part, or its replacement/equivalent for the ones that will be. For example, I know what a trimmer is but there are hundreds of them and I don't know if any 100 ohm will work or not. Same with caps and transistors. I, as well as many others have to rely on the expertise of you who have work successfully on these receivers.

I am attaching the SM sheet that addresses driver board adjustments for the G7500. In my post #39 I gave some readings that I obtained for bias current. In your response #40 you kinda freaked out (please don't take this out of context, I freak out all the time) over the readings and how I got them. Perhaps this sheet will explain why and how I got them.

Thanks again to you and tarior for the advice and response.

looks like a shorted output transistor or open circuit emitter resistors .

 

[kevzep]

looks like a shorted output transistor or open circuit emitter resistors .

Nope, it would be blowing the mains fuse if that was the case...

 

[kevzep]

Thanks again, this is good information. One of the first things I asked for was a complete parts list (if one was available) for this board. Perhaps it fell through the cracks. Even if all the parts are not going to be replaced it is beneficial to know the correct part, or its replacement/equivalent for the ones that will be. For example, I know what a trimmer is but there are hundreds of them and I don't know if any 100 ohm will work or not. Same with caps and transistors. I, as well as many others have to rely on the expertise of you who have work successfully on these receivers.

I am attaching the SM sheet that addresses driver board adjustments for the G7500. In my post #39 I gave some readings that I obtained for bias current. In your response #40 you kinda freaked out (please don't take this out of context, I freak out all the time) over the readings and how I got them. Perhaps this sheet will explain why and how I got them.

Thanks again to you and tarior for the advice and response.

I don't keep parts lists either, it literally takes 10 mins to compile a list and do an order, I also don't archive them as I have most in stock because I do so many.
Just go through the amplifier and make a list, mark the top of the caps with a marker pen as you write them down so you do not double order..

Use a simple single turn 100Ω 500mW trimmer. I use Bournes.

Your reading in post #39 must be wrong. If you are measuring from the test points or across the emitter resistor, you simply cannot have 35V there. If you do the math, it works out to 50 (ish) amps, so, not possible.
It must be 35 mV.....which is about 10 times what it should be, IF you are measuring in th correct place.
This, is where we need pictures of what you are doing.

So, you need to be very clear, the wrong information will make it very difficult for us to help you.

Start again.

If you have got all the things Tarior pointed out, parts fitted, plugged into the DBT, bias trimmers set to minimum, DC offset trimmers set to 50%.
Then we are ready. Take pictures of where you are hooking onto to take the measurement, this way, there can be no confusion.

 

[petehall347]

open/high ohms emitter resistors will cause high voltage to be read instead of mv.s .
how high i do not know with this unit . have seen it with others . will likely cause high offset too.

 

[kevzep]

open/high ohms emitter resistors will cause high voltage to be read instead of mv.s .
how high i do not know with this unit . have seen it with others . will likely cause high offset too.

The ones I have worked on have never had hiZ or open emitters but you do have to eliminate.....

Its reading 35V Pete, that is definitely a meter error, to read that much...

 

[petehall347]

easy things first .
op did say this ...
RE: Post #39 and 40. This is where I
measured the Bias Current. I have a mV
setting on my DMM (Fluke 117 auto
ranging) and got 0. Switch to VDC and got
the 34.48 reading
maybe a blown fuse in the meter . i would have thought it would read OL if out of range .