G6700 no signal pré scaler - Digital problem

[Halisson]

Hello and thanks for reading.
I have read all posts about G6700 display faults, etc.
Mine is cut, lights do not turn on the center TUNE, but turns the TUNE on the left when identifying a poorly tuned radio.
I have a 50mhz oscilloscope, I can not detect any variation from the front end FF-631U, C16, C4 or before R8, the components test basic quickly look good.
I do not have any type of change in the cut numbers of the display, I do not have cold solder in the IC, I have no pre-scaler reading, 2SK61 on gate 11,6vdc.
could it be because my oscilloscope can not read> 50mhz, with grounding in the chassis frame or variable block?
Changing of the Crystal 6,553 mhz without change, I receive changes of the CI H11225 when monitoring on the oscilloscope on tune, etc.
Should I order the IC? The cost of shipping + purchase would leave 4x the initial value than advertised on ebay, I am afraid of not solving.
When switching to AM or FM, the numbers remain the same, FM only FM and MHZ light up, when switching to AM, turn on FM / AM / MHZ / KHZ light up, see photos.
I have the voltage f3060 of TR602 EMITTER 13VDC AND TR601 TRANSMITTER 5VDC and ground is OK.
Thank you

 

[kevzep]

I would say its most likely the MSM5540 chip, when they malfunction the symptoms are usually missing segments, I had one that was very much like what you have there, put a NOS 5540 in and we were back in business. Not sure where you would get one from, I bought one of the last ones around.
The do fail with regularity, you might need to buy a donor unit.

If you can't get the center dot to light up, this is an indication that the front end needs alignment, sounds like someone has had the "golden screwdriver" in there, but it could also be that the segment is not lighting up.
Does it get Quartz lock and receive Stereo?

 

[Halisson]

Thanks for the quick help!!
I get stereo but I do not get quartz lock.

"golden screwdriver" here in Brazil this is common kkkkkkkkkkk, they seem to be afraid of specific tools, and they go out doing what they like, I liked the name !!!

 

[Halisson]

I would say its most likely the MSM5540 chip, when they malfunction the symptoms are usually missing segments, I had one that was very much like what you have there, put a NOS 5540 in and we were back in business. Not sure where you would get one from, I bought one of the last ones around.
The do fail with regularity, you might need to buy a donor unit.

If you can't get the center dot to light up, this is an indication that the front end needs alignment, sounds like someone has had the "golden screwdriver" in there, but it could also be that the segment is not lighting up.
Does it get Quartz lock and receive Stereo?

Thanks for the quick help!!
I get stereo light but I do not get quartz lock.

"golden screwdriver" here in Brazil this is common kkkkkkkkkkk, they seem to be afraid of specific tools, and they go out doing what they like, I liked the name !!!

 

[kevzep]

Yes indeed, those damn people with their golden screwdrivers!! Making life difficult for techs since a long time ago!!

Yeah no quartz lock is another symptom indicative of MSM5540 failure.

I'd start looking for another cheap donor unit.

 

[Halisson]

uou ... I'll have to really care.
here in brazil these equipments are not so common and you will need to buy them on ebay or other medium.
Would you have any for sale?
Thank you for your help

 

[ghazzer]

You might also watch for F-3000 boards for sale if someone is parting out a G-4700/5700/6700 or 7700. There are some minor differences where Sansui replaced some hardwired jumpers with connectors, but the boards are the same.

 

[Halisson]

You might also watch for F-3000 boards for sale if someone is parting out a G-4700/5700/6700 or 7700. There are some minor differences where Sansui replaced some hardwired jumpers with connectors, but the boards are the same.

Tks to help.
My board is 3000. I'm going to get the purchase of one. I will provide an oscilloscope greater than 50 mhz to evaluate the front-end and pre-scaler.

 

[kevzep]

There were two boards as far as I know, the F3000 and the F3300.
They both have the MSM5540.

Should be able to see 50mhz on a 50mhz scope? does it have X10 MAG?

 

[DougBrewster]

The T80 tuner has the chip also

 

[kevzep]

The T80 tuner has the chip also

Good call! Yes it does indeed!!

 

[AUD101]

...and also the TU-719 & TU-919

 

[Halisson]

[QUOTE =
Should be able to see 50mhz on a 50mhz scope? does it have X10 MAG?[/QUOTE]

My oscilloscope is the Tektronix TBS1052, I have the X10 key, it would be the same X10MAG (sorry not to know if this is it).
I marked where I can not read any.

https://imgur.com/a/caUot

 

[ghazzer]

The G-8700 & G-9700 have the F-3088 board, which also uses the MSM5540 chip, but I don't think this board can be installed in the other models of that series.

IIRC, the F-3300 board has the scaler function built in and would require some re-wiring and modifications to replace the F-3000 board. TTBoMK, there is very little documentation available for the F-3300 board, but It does use the MSM5540 chip.

If you have a friend or acquaintance who owns a working G-X700 receiver with the F-3000 board, it is easy to swap the boards. That way you could find out if the rest of your G-6700 is operational.

Just be glad that your F-2980 board is working ! ! !

 

[Hyperion]

The G-8700 & G-9700 have the F-3088 board, which also uses the MSM5540 chip, but I don't think this board can be installed in the other models of that series.

I think the suggestion is to remove the MSM5540 chip from the donor board and install it in the existing tuner board - not try to transplant the whole board from another model into the faulty one, if that what what you were referring to Steve?

 

[kevzep]

[QUOTE =
Should be able to see 50mhz on a 50mhz scope? does it have X10 MAG?

My oscilloscope is the Tektronix TBS1052, I have the X10 key, it would be the same X10MAG (sorry not to know if this is it).
I marked where I can not read any.

https://imgur.com/a/caUot

[/QUOTE]
You probably just need to get your triggering right, try the Auto-scale function....
I am an analogue scope guy, I have a 300mhz 4ch Tektronix and a 100mhz tek as well, I can 200mhz on my old 465.....
takes a bit of fiddling around, but the digital should be able to autoscale and do it for you....

The best thing to do with this MSM5540 is if you can get the same board, the F3000, just fit the whole board, its you get any other board, like the F3300, they wont go straight in, so you'll have to desolder the chip.
Just be sure you have a good desoldering tool and dont use too much heat, wear an anti static wrist band while you are doing it too.

 

[ghazzer]

If you happen to get a working F-3000 bd it is much easier to swap the bd than swap the chip. That might also help with the original troubleshooting.

TIP: Should you locate a replacement chip you should purchase a 40 pin socket for the board. It is much easier & safer to install the socket then press in the chip, than to solder in the replacement chip.

 

[kevzep]

I just soldered mine in, no problem if you have a good iron, but the socket is an elegant solution.

 

[ghazzer]

I think the suggestion is to remove the MSM5540 chip from the donor board and install it in the existing tuner board - not try to transplant the whole board from another model into the faulty one, if that is what you were referring to Steve?

Sorry John, my answer wasn't very clear, but I do suggest the transplant.
If you are fortunate enough to find an F-3000 board, I would just go ahead and swap boards. The problem is solved if everything works and you have no reason to unsolder a 40 pin chip twice and solder it in as a replacement. At that point I would just leave the second board in place, button it up and enjoy the show.

The F-3000 in my G-6700 has all the external connections going thru connectors, and there are only 2 screws holding it in place. I have seen some earlier versions in G-4700s that have some external jumpers soldered to the board, but still useable.

I just soldered mine in, no problem if you have a good iron, but the socket is an elegant solution.

Hopefully you would not need to replace it again, but using the socket prevents damaging the NOS chip with overtemp during soldering.

 

[kevzep]

I wouldn't worry about damaging the chip with heat, its more static discharge, I have solder hundreds of static sensitive chips, a lot of SMD ..... over temp is not an issue with a good iron, just make sure you are wearing you anti static wristband when you are handling the chip.
But a socket is cool, and in my work I actually always put sockets on chips I replace.....