TU 9900 Problems

danrclem

Super Member
I bought a TU 9900 knowing that it didn't work correctly. I got it for a decent price so if I can't get it working maybe I can at least get my money out of it.

I took the top off and powered it up. The signal meters and dial window lights up and the power light works also. The am signal indicator was working now it's not. The fm indicators didn't light up either. I can smell an electrical burning smell but no smoke. The transformer feels like it's getting pretty hot but that may be normal. I didn't take the bottom of but the top side looks fairly normal besides being dirty.

Anybody have any ideas.
 
Is the mains voltage setting correct ?

It could be a shorted turn on the transformer or it could be a shorted rectifier diode or filter cap. Disconnect the secondary of the transformer and see if it still runs hot.
 
A tuner does not draw much current, so the transformer does not have much work to do, and it should not heat up. Rabbit is correct, the voltage selector should be checked.

The rectifier and the filter caps are not expensive, nor are they difficult to replace, so that would be the next thing I'd look at, after checking the resistance of the primary and secondary windings in the transformer as already mentioned.
 
First off I'd like to thank you for the replies. Second I'd like to say that I have no experience in electronics but I do have a couple multi-meters and I can solder.

By the mains voltage setting are you referring to the clip on the left side (facing the front of the tuner) that can be set for different voltages. If so I have checked that and it is set for 120 which I think is correct. There is also a switch in the same area that has 2 settings. Which way would be correct?

I've already closed it back up but is the secondary of the transformer the part wrapping around the outside?

Would I be checking the transformer for resistance? If so how much resistance should it have?

When checking rectifier and filter caps (which I have no idea which ones are which) do I also check for resistance. Do I check them on the board or do I have to remove them.

Thanks for any help that can be given. I'm close to retirement age and am trying to improve on my existing system without spending a ton of cash. When I do retire I want to listen to some good music and it would be fun to learn and tinker around on vintage equipment.
 
Well, the TU-9900 is one of the "best of the best' tuners, so great choice. The transformer windings should not be visible at all, neither secondary nor primary. The service manual should be available on HiFi Engine, a website. Most of the answers ought to be there. You might have to register to obtain the download, but it's no big deal. If nothing works, I might have it, and if so, will be happy to send it on to you.
 
Well, the TU-9900 is one of the "best of the best' tuners, so great choice. The transformer windings should not be visible at all, neither secondary nor primary. The service manual should be available on HiFi Engine, a website. Most of the answers ought to be there. You might have to register to obtain the download, but it's no big deal. If nothing works, I might have it, and if so, will be happy to send it on to you.

Thanks Tinnkindling, I'll go there and see what I can find.
 
Can you post a pix of the front & top ( internal ) of the unit? If the unit is fubar.. I need a front panel… I could take it off your hands.. BUT now onto testing 1 st if it is a " NORMAL" tuner, the dial face will goon FM from 88 mhz to 108 mhz. The Japan ones go 76 Mhz to 90Mhz ( Whoops ) the Japan ones are ONLY 100volt...
 
The VOLTAGE selector is on the top of the internal chassis, left rear next to PT-01 Power transformer ( send Pix )
 
If you are set @ 120Volts ( I assume your in the USA ) …
Locate the F-2527 board. ( to the right of the power transformer ) .
Get out your DC meter.
Set for 0~20 volt range.
POWER OFF ON TUNER
Locate connectors 06-07 & 08 ( opposite the fuses )
Hook the positive of your meter to 06
Hook the negative of your meter to 07
Power ON
Should have about 13 volts there
Power OFF
Move positive ( red probe ) to connector 08
Power ON
Should have MINUS 11.5 to MINUS 13.5
Power off
Report back
 
Thanks vigman. It is the 88mhz to 108 mhz. I probably won't be able to look at it until this weekend but as soon as I find anything out I'll report back.
 
I'm editing my post because I wasn't getting any readings but found out I wasn't getting a power connection. Connection 06 and 07 was reading -.46 and after warming some dropped to -.31. Connection 07 and 07 was reading -2.29. Transformer was getting warm again Bad transformer?

It must have been blowing fuses because there was a 25 amp fuse where a 3 amp should have been and 3 amp fuses where 1 amp fuses should have been.
 
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First things first

Lets completely take the load off the transformers... and measure what it can do with NO LOAD and see if it still gets hot... See notes on pix...

Post results here
AC Volts

Main
1-3

1-2

2-3

Then the other 2 windings for the lights
 

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Do these readings need to be in AC or DC? I was assuming DC but I wasn't getting much of a reading.

The transformer is staying cool with no load.

The fuse to the left on the pic is 04, next is 01 and then 03. The pin to the right of the fuse pins is 02. Do I still check by the numbers and not the order that your diagram has?
 
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I put the fuses back in and read 06, 07 and 08 again in ac. I went to the garage and got my multi-meter with a sweep hand. 06 and 07 had no reading no matter how I had the polarity. 07 and 08 read 5v one way and 0 the other.
 
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