Sansui TU-919 Works but LCD Display not working...Where to start?

[audiodyssey]

Ok, so the LCD has digits, partial digits, but doesn't respond when turning the dial.
Does it have to be the IC...or what should I begin with...?

 

[kevzep]

Its the IC, the MSM5540 is the display driver, when they fail, or partly fail some segments will stay on and some wont come on at all.
The only way around it is to replace the chip which are now getting very very hard to get.....You might have to find a donor unit as I think pretty much most of the NOS stock on planet earth are now depleted.

 

[Sansuiman]

This MSM5540 driver IC is likely at fault, but it has been found before that the crystal (which is the reference for the CPU clock) that is part of the display driver circuit has failed causing unpredictable behavior from the IC. Most applications with this IC used a VF display panel, the TU-919 is unique in that it uses 7 segment LED displays, and so the driver circuitry is slightly different. May be dropping resistors that have failed causing loss of some segments, though unlikely. I only point this out so you don't write off the IC prematurely.

Note too that the MHz and KHz markers at the right end of the frequency readout are actually 6 volt micro lamps, not LEDS, behind a red lens with a mask for the respective band markings.

 

[UncleBingo]

I had one of these that the display was lit but didn't follow the frequency. Changed the crystal. Boom. Worked. try it before digging further in.

 

[DougBrewster]

a cheap donor unit is the TU80 tuner..

 

[kevzep]

I had one of these that the display was lit but didn't follow the frequency. Changed the crystal. Boom. Worked. try it before digging further in.

If there are segments missing and segments lit all the time, then the MSM5540 display driver is faulty.
Its common for the analogue dial to be out from the digital readout, but if the actual frequency is off then yes the pre-scaler or clocking crystal on the F3000 is a good place to start.
However, I do not believe this is the case here.

a cheap donor unit is the TU80 tuner..

They used to be, but they are not that cheap any more sadly......

 

[cantonkid]

i have a 919 thinking it should have the black flags done and probably this led section gone over it works fine now should i leave well enough alone on the leds ? how many hours should it take to do the black flags ?

 

[lbcgav]

Not allowed to post ebay links in the forum, just saying when you wonder where they went when mods delete both our posts...

Strange. Just trying to help out. Don't see how helping out someone shouldn't be allowed.

 

[eizner23]

Consolidated electronics has em but not cheap

http://www.ceitron.com/cart/advanced_search_result.php?keywords=MSM5540&search_in_description=1

 

[kevzep]

Strange. Just trying to help out. Don't see how helping out someone shouldn't be allowed.

I know, but the rules are no ebay links.
I was just saying in case they delete our posts with the links.

 

[kevzep]

Consolidated electronics has em but not cheap

http://www.ceitron.com/cart/advanced_search_result.php?keywords=MSM5540&search_in_description=1

They were out of stock last time I tried them, it still comes up in the search but when you go to buy one you get an email saying "temporarily out of stock"..

 

[lbcgav]

I know, but the rules are no ebay links.
I was just saying in case they delete our posts with the links.

Thanks for the heads up.

 

[Sansuiman]

T-80 used to be an inexpensive donor for the chip and the VFD used in the TU-719 and several of the upper range G-x700 and x900Z series receivers. Of course, the fact that they were getting snatched up for parts and that all Sansui gear has appreciated in value due to demand, they are no great deal anymore as a parts donor.

It's also a shame to junk a bunch of T-80's. Even though they aren't high performance tuners, they are (or were) nice entry level gear for those with a limited budget. I own one in silver along with an A-80 amp, SE-9 EQ, D-550M tape deck, RA-990 reverb and RS-7 remote system add-on for a nice, modest performance bedroom system that looks great to boot. I'll note that the silver variant of this series is much more common than the black one, for what it's worth.

 

[kevzep]

T-80 used to be an inexpensive donor for the chip and the VFD used in the TU-719 and several of the upper range G-x700 and x900Z series receivers. Of course, the fact that they were getting snatched up for parts and that all Sansui gear has appreciated in value due to demand, they are no great deal anymore as a parts donor.

It's also a shame to junk a bunch of T-80's. Even though they aren't high performance tuners, they are (or were) nice entry level gear for those with a limited budget. I own one in silver along with an A-80 amp, SE-9 EQ, D-550M tape deck, RA-990 reverb and RS-7 remote system add-on for a nice, modest performance bedroom system that looks great to boot. I'll note that the silver variant of this series is much more common than the black one, for what it's worth.

I know I have raided a few T80's, and then felt guilty about it...such a shame to just raid it for the F3000 board and trash the rest, at one stage I had three under my bench, but threw them out when I moved house...

 

[audiodyssey]

WOW you guys are awesome. SO...The T-80 has this IC in it? I am SORRY but that T-80 in Santa Ana CA may end up being my donor...

 

[Sansuiman]

Yes, the T-80 tuner has a MSM5540 ic in it. Will need to be desoldered and installed in the 919, as the circuit boards used in each model are different so can't just do a board swap. Don't smoke the chip desoldering it though. It's a 40 pin DIP, so takes some effort to get out clean. Vacuum soldering rig is a must, IMO.

 

[kevzep]

WOW you guys are awesome. SO...The T-80 has this IC in it? I am SORRY but that T-80 in Santa Ana CA may end up being my donor...

Yes, well one of those might just be heading my way as well as I have a sick MSM5540 in a G6700 here as well.

You need to be VERY careful desoldering the chip, you need to take all ESD precautions, do not use too much heat for too long as you will damage the chip.

Really you want to be using a decent solder station with a proper vacuum solder extractor, you wont do it easily with braid or a spring loaded hand pump...

 

[DougBrewster]

you wont do it easily with braid or a spring loaded hand pump...

that's the way I did it but spread the heat around. Don't keep going for adjacent pins, go from one end then the other, or side, and take a couple of minutes break after say six or so pins, to let it cool

 

[kevzep]

that's the way I did it but spread the heat around. Don't keep going for adjacent pins, go from one end then the other, or side, and take a couple of minutes break after say six or so pins, to let it cool

I just use my Pace MBT, 30 sec and she's out.....

 

[audiodyssey]

Thank you to everyone and advice taken on chip removal. I'm going to have an old, patient pro remove and install the chip for me.