Sansui T-80 Digital Display Locked

[edog]

I just picked up a Sansui T-80 Tuner. Looks good and it seems to work fine but the digital display is locked on 177.7 in FM. The AM / FM and kHZ / MHz display as they should and the period disappears when I switch to AM displaying 1777. Any suggestions on how to repair this?

The schematic shows the display being fed by an MSM5540 chip. I hope this isn't the problem, because I haven't even been able to find a datasheet on this chip, let alone a replacement.

 

[ModernClassic]

It is quite common for the MSM5540 chip to fail. I could not find new replacement either, I ended up buying a working T-80 just to get this chip!!!!!!!!!

 

[edog]

Thanks. That's not the reply I was hoping for. I guess I'll keep looking for the chip.

 

[edog]

Tuning Light & Quartz Lock Problem

I have one other problem with this receiver - the tuning 'eye' never lights up in the center. The triangular lights on either side of center work, |>o<| but I assume when I'm centered on a freq they should both be lit with the center light. (I know the center light itself works, because it flashes on power up). Is this connected to the quartz lock circuitry? That light doesn't come on either.

 

[ericson38]

I had a G 5700 develop this problem exactly, and actually bought a perfectly good T80 on ebay last year so I could swap the digital display board into the 5700. The operation was not a success, so I determined that the color codes of the xtals on the two units were different, and used the G5700 manual to set four jumpers on that digital mezzanine board to accomodate the color codes correctly, still didn't work.

I won't buy another GX700 Sansui for this reason, all though they are very nice looking receivers.

 

[edog]

Thanks Ericson. I was just looking at the jumpers last night - does your board have all the diodes in it? I noticed the remnants of a cut jumper on A, and the B jumper is a wire that goes to the other end of where a diode should be (the diode is missing). The jumper on C is a bare wire that's correctly connected to the end of a diode. My "blue" crystals call for jumpers B and C which is what I got - except for the missing diode.

I noticed you're just down the street from me. Do you still have the board out of the working T-80 - it'd be interesting to see if it works in my receiver. If it doesn't, then we would know it's another problem and not the F-3000 board.

 

[ericson38]

Thanks Ericson. I was just looking at the jumpers last night - does your board have all the diodes in it? I noticed the remnants of a cut jumper on A, and the B jumper is a wire that goes to the other end of where a diode should be (the diode is missing). The jumper on C is a bare wire that's correctly connected to the end of a diode. My "blue" crystals call for jumpers B and C which is what I got - except for the missing diode.

I noticed you're just down the street from me. Do you still have the board out of the working T-80 - it'd be interesting to see if it works in my receiver. If it doesn't, then we would know it's another problem and not the F-3000 board.

I sold that receiver as a parts unit last month (it has the reworked T80 F3000 board in it now). If I can locate the bad but original F3000 board from the G 5700, I'll post a note on how it's wired and what the colors are for the oscillators.

 

[rasenthiran]

Guys,

Just bought the tuner a week ago,everything works fine but the quartz lock does not lock the station.sound goes off after the reception is tune and the green led lights.hope for T-80 owners advice.

 

[kevzep]

I have one other problem with this receiver - the tuning 'eye' never lights up in the center. The triangular lights on either side of center work, |>o<| but I assume when I'm centered on a freq they should both be lit with the center light. (I know the center light itself works, because it flashes on power up). Is this connected to the quartz lock circuitry? That light doesn't come on either.

No Quartz lock
Display segments failing or not lighting up when they should.
These are problems associated with the MSM5540 chip failing......

I ahve had a lot of experience with these tuners and I can tell you its the chip for certain.

I had a G 5700 develop this problem exactly, and actually bought a perfectly good T80 on ebay last year so I could swap the digital display board into the 5700. The operation was not a success, so I determined that the color codes of the xtals on the two units were different, and used the G5700 manual to set four jumpers on that digital mezzanine board to accomodate the color codes correctly, still didn't work.

I won't buy another GX700 Sansui for this reason, all though they are very nice looking receivers.

You have to be careful swapping the entire board out, because there are two different versions of this board, and you cannot swap them.
In the early GX700's those F-3000 boards are different from the later version. You may have had an early G5700.
The T-80 uses the later version.
The only way to do this successfully is to remove the chip from the T-80 tuner and replace the faulty one on the board in your G5700.
You have to very good with the de-soldering, because it is easy to damage the chip with too much heat.....Best to use a de-soldering pump, wick uses too much heat.....
When they revised the GX700 series, they changed the power supply/amp driver board, there were some changes in the power supply section to the tuner among other things.

Guys,
Just bought the tuner a week ago,everything works fine but the quartz lock does not lock the station.sound goes off after the reception is tune and the green led lights.hope for T-80 owners advice.

Replace the MSM5540 chip, this is classic MSM chip failure.

 

[rasenthiran]

hi kev,


Is it a rare chip??the msm5540 or it is easy to get from electronic parts shop??if thats the case,i can get it and give it to the tech to change it.

 

[kevzep]

hi kev,


Is it a rare chip??the msm5540 or it is easy to get from electronic parts shop??if thats the case,i can get it and give it to the tech to change it.

The chip is rare and difficult to find.....the easiest option is to find a cheap T-80 tuner and use the chip from it.....
I was very lucky and found one from Consolidated electronics in the USA about 2 years ago, and when I went to order another one as a spare they had run out of stock and told me they had discontinued as a supplier for the chip, they were becoming too difficult to source....

 

[rasenthiran]

kev,thanks for ur advice. is there any way to bypass the quartz lock and use manual tuning for stereo fm listening??Quartz lock causes the sound goes to mute.I find its a good tuner to collect.

 

[kevzep]

kev,thanks for ur advice. is there any way to bypass the quartz lock and use manual tuning for stereo fm listening??Quartz lock causes the sound goes to mute.I find its a good tuner to collect.

What I found when my chip had failed and I had no quartz lock, is that the tuner drifts off the station, if you turn the FM Muting off, when you lose quartz lock you will still have audio, but you will be picking up static as the tuner is no longer actually on the station.....
I suspect the design of the tuner actually relies on the quartz oscillator to stay on the station.......So when that fails, the tuner is rendered almost useless......

I think if you find a GX700 series owners manual or brochure, they explain the "new digital quartz lock" tuner and how it all works ......
There might even be something on it in the Service manual.....

 

[ChristianB]

Tuning Light & Quartz Lock Problem

I have one other problem with this receiver - the tuning 'eye' never lights up in the center. The triangular lights on either side of center work, |>o<| but I assume when I'm centered on a freq they should both be lit with the center light. (I know the center light itself works, because it flashes on power up). Is this connected to the quartz lock circuitry? That light doesn't come on either.

Replying back on a very old discussion, 10+ years later!, still it may help someone with the Quartz Lock issue

I found a fix to the Quartz Lock issue. In my case it will not lock and tuning tend to be unstable. After this fix it is A-OK : Look in service manual p2, step 2, it says to measure voltage between TP02 & TP03 on F-3130 board and adjust T02 on F-3130 board to get DC 0v ± 0.1v

Got it very close to 0v and now Quartz Lock works fine.

 

[edog]

Replying back on a very old discussion, 10+ years later!, still it may help someone with the Quartz Lock issue

I found a fix to the Quartz Lock issue. In my case it will not lock and tuning tend to be unstable. After this fix it is A-OK : Look in service manual p2, step 2, it says to measure voltage between TP02 & TP03 on F-3130 board and adjust T02 on F-3130 board to get DC 0v ± 0.1v

Got it very close to 0v and now Quartz Lock works fine.

Wow - 15 years tomorrow since I first posted this. I'm almost embarrassed to say the tuner wound up on a shelf and fell to the bottom of my list of things to be tinkered with. But now that you brought it up, I think I'll have another look at it.

 

[ChristianB]

Wow - 15 years tomorrow since I first posted this. I'm almost embarrassed to say the tuner wound up on a shelf and fell to the bottom of my list of things to be tinkered with. But now that you brought it up, I think I'll have another look at it.

Just in case you also have "unable to hold Frequency after power cycle", this one I fixed with VR03 on F-3000 Board. I did not do the whole procedure, I just tweak VR-03 on F3000 and it got fixed. I found that solution here: https://audiokarma.org/forums/index...e-to-hold-frequency-after-power-cycle.977444/

 

[alifamzari]

Replying back on a very old discussion, 10+ years later!, still it may help someone with the Quartz Lock issue

I found a fix to the Quartz Lock issue. In my case it will not lock and tuning tend to be unstable. After this fix it is A-OK : Look in service manual p2, step 2, it says to measure voltage between TP02 & TP03 on F-3130 board and adjust T02 on F-3130 board to get DC 0v ± 0.1v

Got it very close to 0v and now Quartz Lock works fine.

Register just to say this.
It works! Mine was around +0.05, reducing it closer to 0.01/0.02 solved the digital quarts locked muting audio.

 

[ChristianB]

Register just to say this.
It works! Mine was around +0.05, reducing it closer to 0.01/0.02 solved the digital quarts locked muting audio.

Glad my message helped