The OFFICIAL MSM5540RS/M5540 Gx700 40pin IC Thread! NUDIES

trueno92

Active Member
Hi All,

OK I am creating this thread with the intent to consolidate all the known info on the MSM5540 chip and replacing it.

I am new to this, and in everything i know so far, has been read and mainly collected from AUDIOKARMA, so I hope this can give back to this wonderfully knowledgeable community of hobbyists!

THE CULPRIT

In an age that FM radio has more competition than ever for streaming music/radio shows, I found FM on these vintage Sansui units very refreshing. Maybe it was because it can flawlessly pull in every station under the sun! I don't think I have ever owned an FM tuner of any credible mention and this really surprised me. The number of stations and the clarity was new to me.

But to look at the handsome unit, was just glaring back with a black-eye:
IMG_20150203_130814.jpg


Yup, the digits and quartz lock were non-functional.

Although cosmetic and not affecting the performance of my tuner, I wanted to repair this back to its former glory. Hey, I got into vintage gear for the ability to fix whatever I could!

THE CULPRIT:

My unit has the F3220 display board. You may have the F3000. I noticed that the F3220s are in the units with the non-chamfered heatsinks on the back and from my sample of pics on the net, the F3220 are mainly in production with 1980 serial numbers.

IMG_20150203_123625.jpg


IMG_20150203_123130.jpg

NOTE D05 in the center of the picture. SHOULD THERE BE SOMETHING HERE???

REMOVAL:

Pretty straight forward. Braid and the iron working 2-3 pins at a time. I found this easier than cutting each pin from the IC and working those out. Once the chip is free it simply falls out
(IF THIS IS NOT BEST-PRACTICE FOR IC REMOVAL, PLEASE REPLY TO THIS THREAD AND I WILL CORRECT THIS SECTION)

IMG_20150203_124302.jpg


and old chip out, perfectly usable condition
IMG_20150203_125433.jpg


NEW IC. OLD IC
IMG_20150203_125515.jpg


SOCKET INSTALLED
IMG_20150203_130316.jpg

(TESTED, works)

IMG_20150203_130247.jpg


NEW CHIP INSTALLED
IMG_20150203_131135.jpg


I later revised this to add: USE another 40 pin socket on your new M5540 chip. If you have to troubleshoot your work, it will be easier on the chip as you don't have to worry about bending pins. So basically you will be add a socket to the board and another socket to the chip.

My system now has the quartz lock feature and it works perfect, however my digits still don't read correct now locked at 167.6 on AM and FM.

I checked the tuning pot in the service manual for step 5 of the FM tuner calibration but it highlights adjusting TC06 on the front-end (which i learned later is the actual FM moving tuner meat slicer thing). ON my 6700, this did not correct the digits, but instead worked more to calibrate the actual tuner to the scale...

SERVICE MANUAL SAYS:
image.png

NOW WHAT DOES THAT FIRST INSTRUCTION MEAN???
"... make the dial pointer go round the dial scale at once by turning knob"
I assumed this to be, run the dial pointer completely across the scale from beginning to end

And this is what I got for locating TC06
image.png

6th entry down on the right side

I am hoping you experts can assist me on this!
 
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if anyone has a working F3220 board, can you take a look at the D05 and the jumper above and tell me if it lines up with my pictures displayed?

not sure if these were cut from the factory.

from looking closer at it, it looks like there is some option to use D05 or D06 and they both terminate at the same place...
 
Guys, any thing else I should look at? Is the IC really defective? The rest of my tuner works quite well..

Does anyone have another spare f-3220 board that they could donate to my cause? :(
 
Do you have anyone nearby with similar model with socket already installed? They might be able to test the chip for you... Where are you located?
 
Yeah, I wish! I am out in TORONTO, Ontario, Canada...

I've shot Kale an email. I am hoping at the worst, he could post me another discounted chip or best-case, exchange this suspected defective one...

I just want to rule out my G6700 isn't the cause.... but thats exactly what you suggested!! great minds troubleshoot alike!
 
Does AM counting work at all? You have to remember there is a pre scaler circuit before the 40 PIN IC. When you switch between AM and FM does the display change?
 
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I just read where AM AND FM don't work in yours in ANOTHER post. Check pin5 voltage on the 74LS90 chip and post your finding.
 
Hi, Andrew told me by ebay that he has the same problem after he installed chip… I just wish to say that display electronic circuit is not for someone who dont know how it works… especially it is not good to make any kind of adjustment on front-end without you are sure what you are doing. You can make things worse, so later someone who knows all about this, must spent a lot of time to get tuner at proper function…

Because of all, I have written at my auction that installation job must be done by qualified technician, not because replacement of that chip, but because you should to know check parameters of those circuits. I wish if I could know speaking English much better to bring you thought all testing procedure (and I wish to have much more free time than I have now), but I could not… now I have one TU919 what it has a display problem too, and the display chip is OK on it, so I am still searching to find what is going on… and I have FM signal generator, I have stereo signal generator, I have oscilloscope, I have True RMS DMM…

Guys, something you can fix yourself on yours vintage audio, but something you cant… especially if you don’t have a knowledge and (very important) testing equipment (especially for tuners)
So Andrew, all what I can say you, that chip was brand new, unused and packed on antistatic pad, and until now, I had no complaints about it, but I am sure that something else here is problem…

If yours technician would say you that chip is defective, I would send you a new one, free of charge (but you should pay shipping for sending).
Again, I would repeat, yours technician should check display electronic circuit board, and after he checked all and after he told that chip is defective, I will send you a new one again…
 
Hey Kale, it looks like Bktheking has some areas for me to check. No worries, I am leaning to suspect my f3220 board needs a closer look!
 
If the display on these shows the wrong frequency and doesn't change when you turn the tuning knob, it is not getting the signal from the local oscillator. I don't have the schematic in front of me but from what Bktheking says the signal from the LO goes to a prescaler which converts the 100+MHz LO signal to a lower frequency. You need an oscilloscope to check the output of the prescaler. If you see no signal, you really need a scope with at least 100MHz bandwidth to check to see if the prescaler is getting the output from the LO. If the tuner is working but the display is not, then the LO is ok and the signal is being lost. There is usually a coupling cap in series with the LO signal and I have seen them go bad.
If you have signal coming from the prescaler, then the oscillator / crystal for the display chip could be bad. If it doesn't have a reference it can't count.
All these things need to be checked before replacing the chip!
 
gents, thanks so much for chiming in.

a couple of things: So, getting into vintage audio is new to me. No surprise, right? I have googled out audiokarma and have never read one instance of this coupling cap going bad! In every case, the replacement chip seems to fix the unit! Even in my case of display showing 177.7/1777 in FM/AM! I initially thought it would be an open and shut case, but this is getting more interesting!

So I hope to learn something from the vast stable of knowledge you guys can present! Thank you in advance!

I have repaired electronics before.. but a scope with 100mhz bandwidth i do not have........

What I know so far:

Quartz lock works
FM and AM show the same digits 167.6/1676
Voltages for the Chip seem good
Chip is known good.

I think my only option is to check the in-series coupling cap?

Since I am still a tiny grasshopper at this:
image.png


and note, I have an F-3220 board which doesn't appear covered in this service manual.. so I can use this to cross reference

image.png
 
also I assume my xtal or crystal is known good as quartz lock is working correctly.

Here is the prescaler board F-3010

image.png
 
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The board layout / block diagram doesn't help. I need the schematic.
Does the radio work? Do you receive stations properly?
I got the service manual. The coupling cap is C16 on FF631U, the FM Frontend. From there, the signal goes to the Prescaler Board and there is another coupling cap, C01 and resistor R17, which should also be checked. Without a scope, though you are shooting in the dark. You can try replacing these caps and hope for the best. Also check the connectors and cables connecting the Prescaler to the Frontend.
 
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Finally in taking a look at the service manual map, it lists F-3010 to be under the Front end board, and can be seen from the bottom if the cover is removed.

on my unit, f-3010 is not there. has anyone seen this board placed anywhere else?

I AM SO CONFUSED!!!

INSTRUCTION:
image.png


REALITY:
IMG_20150204_133007.jpg



HELP!!
 
The board layout / block diagram doesn't help. I need the schematic.
Does the radio work? Do you receive stations properly?

Hi Dr.

Radio works a treat. works perfectly pulling in everything under the sun.

Here is the schematic as requested:

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brb gents, I have to do some volunteer work at my children's school.

kindergarten is so fun... hah.
 
I got the service manual. The coupling cap is C16 on FF631U, the FM Frontend. From there, the signal goes to the Prescaler Board and there is another coupling cap, C01 and resistor R17, which should also be checked. Without a scope, though you are shooting in the dark. You can try replacing these caps and hope for the best. Also check the connectors and cables connecting the Prescaler to the Frontend.
There should be 2 shielded cables going to the frontend. One goes to the IF board. Follow the other one and you will find the prescaler.
 
ok i think i may be crazy but the prescaler is built in as part and parcel of F-3220?

Doesn't look like it according to the schematic.

But it wouldn't be unusual for it to have been amalgamated, sometimes things like that happened in later production and were never updated in the schematics/manuals.
 
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