Carver TX-11 Questions?

Sorehead

Sorehead

New Member
Would like to communicate with anyone who has a TX-11. I have been given the task of trying to figure out what is causing this unit to remain on the quiet side. No hiss, No sound, nothing when plugged into his amp. This is an FM only unit and I can't find any schematic for this unit as of yet. It is different from the TX-11A. I would just like to ask some questions about how it is supposed to operate verses what it does so far. I have found several things that make you go hummmmmm! Any help and thoughts appreciated.
 
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Welcome to AK!

Sorry, I don't have a TX-11 or a source for a schematic, but in this kind of situation I would look at what IC chips are used, find the datasheets for them, and use the datasheets to guide me in signal tracing. Actually, before signal tracing, I'd identify the power supply pins and make sure the chips were getting appropriate power.

I'm assuming you've tried things like making sure the antenna is good, disabling FM muting, seeing whether AM works, yadayada...

Good luck,

chazix
 
The TX-11 is FM only. The 2 voltage supplies measure -12.45,+12.35 and +11.30 and-11.30. Certainly not perfect but don't believe that its enough departure from the norm to cause this issue however as we get deeper into it, we will see. Most of my time has been spent visually inspecting the boards for obvious issues. I have found some caps getting warm. A recap at some point will need to be done. The only board I have yet to open up is the front tuner board looking for something broken or or questionable to the eye. I did find a broken wire at one place but it didn't have any impact on it operation. It has just one output and that is a left and right output. This unit when it comes on stays locked on frequency and the frequency memory still has whatever has been chosen. I can manually tune the unit but there is no indication of receiving any station including local. Stereo pilot light never comes on. Its just dead quite no noise, no hiss no hum, no nothing. There are two main boards in this unit and I had already done what you suggested with the various IC's and with what information I have found the IC voltages on one board to be near normal. The main board I have not been able to do much with. That's where it stands at this time. I appreciate your response. I will keep looking for a correct schematic.
 
Also don't have a schematic and don't have one a TX-11. But experience tells me often there is a separate third supply at 5 to 7 volts for the display and control.
 
A good place to look for troubleshooting assistance and possibly a schematic would be over at TheCarverSite. I have a TX-11, but it is the (a) model--there was also a (b) model as well, but those are pretty rare.
 
I am looking at the TX-11A schematic. I have never seen nor worked on one. I'd be figuring out how much diff there is between the "A" model and the one you have.
Definitely go over the TX-11A manual first or you will have no idea what to do nor where to look. Then it may require some good test equipment and knowledge to find the possible 10 cent diode.
Lots going on there. As said above always start with the power supplies. Then inject a signal and trace it through. Easier said than done.
 
rcs16 said:
I am looking at the TX-11A schematic. I have never seen nor worked on one. I'd be figuring out how much diff there is between the "A" model and the one you have.
Definitely go over the TX-11A manual first or you will have no idea what to do nor where to look. Then it may require some good test equipment and knowledge to find the possible 10 cent diode.
Lots going on there. As said above always start with the power supplies. Then inject a signal and trace it through. Easier said than done.
Click to expand...
There are many differences between the TX-11 and TX-11A. The TX-11 is FM-only, while the TX-11A can also receive AM. Also, the circuit is rather different, to the point where at least some consider the A version to sound better than the original. I picked up an original several years back at a surplus sale, and it works fine except for the fact that it periodically suffers 'amnesia' at power-up, forgetting all its presets and resetting to 87.5MHz. :no: Anyway, manuals and schematics for the TX-11 can be found here.
-Adam
 
Wow, there is a lot going on in there! But if one can rule out a power supply issue, and if the symptoms persist in both wide and narrow mode, then the problem pretty much has to be from the detector to the MPX decoder (inclusive). I would try injecting audio at the output of the detector chip and see if that gets through; if it does, most likely detector; if not, most likely MPX.

Oh - except there do seem to be all sorts of ways that the signal can get muted, and failures in some of that functionality could take out both L and R audio.

I can see where a proper schematic is going to be really helpful!
 
First, I appreciate your responses and attempts to help. I will need to study the schematic more and I want to study the power supply voltages more. I will follow up on the suggestions presented and see what we find.
 
As far as the basic design, I do not see a whole lot of difference in the FM sections between the versions. So it is an exercise of testing voltages, checking each functional block, RF FE, IF, filters, detector. You can scope/monitor pin 6 of the LA1235 FM detector, (TP205) but has muting capabilities, pin 12 iirc. It always good to read the LA1235 and other IC data sheets to understand more on how those parts work.
O/p of D402 is the IF level detector, it tells you the if it is working okay up to that point. Tons of stuff to check, could right a book.
 
Just an update, rcs16, thanks for your thoughts on the chips. I got the schematic for this thing and at least it tells me where the voltages should be. Hopefully that will help. I am having trouble finding readable data sheets for the various chips. All the data sheets that I have found for the most part are in Japanese or Korean and use less to me. For example the LA3381 per the schematic show pin 12 having a voltage of 1.4 volts on that pin however I read 15 volts on my voltmeter. This is the ppl stereo chip. The other chips we are just getting to. Any place to get some use-able data sheets. rcs16 what should be seen at pin 6 of the fm detector, what scope pattern?Voltage reading? I have not started to attempt to signal trace until I determine status of some more of these chips. Any thoughts or suggestions appreciated.
 
I already had found that data sheet but thanks for your input. One of the problems with the unit is no stereo pilot light indicator.
 
Maybe this will help...

TC9147BP IC & Trim Cap to repair CARVER MXR RECEIVER TX-2 TX-11 Tuner TC9147

Thread on dead TX-11

I remember seeing this a while back and was able to find it using a bit of sleuthing with the wayback machine.

Anyway this is what I was able to find:

https://web.archive.org/web/20150718045110/http://home.onemain.com/~jvandyke/id8.html


How to Repair Carver TX-11a, TX-11b Tuner
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"My TX-11a is having some problems with the AM and FM audio cutting out intermittently after the unit is in operation for 30 minutes or so."
"After almost two decades of trouble free service my TX 11 has stopped working. The display shows .0 and the presets don't work. I saw that one sold on eBay yesterday with the same problem."
"My tuner's search buttons are a little flakey. They work but are erratic."
"I remember watching TX-11 ads on ePrey a number of months ago, and I stopped watching to TX-11 tuners because somebody who appeared to be knowledgeable about them was asking a lot of questions about them to the seller. The bidder had stated that there was a problem with the TX-11 tuners in the initial production run..."
"My MXR-130 Carver Receiver is not working properly. The tuner does not lock into any stations and then becomes inoperative. It occassionally locks into a frequency for a short time but then shuts down and displays meaningless data."

I bought my eBay TX-11a with similar pre-existing problems.
Did I mention I'm really cheap?

The green trimmer cap TC501 on the tuner chip crystal oscillator fails. (who would believe a trimmer cap would go bad?)
Picture is with bottom removed, arrow pointing at trimmer at front of unit.
Undoing top plastic PCB mounts is enough to tilt the board to solder.



Replacement cap is from Mouser:
GREEN 9.0-50 pF
Xicon ceramic trimmer capacitor
24AA024

http://www.mouser.com/search/ProductDetail.aspx?R=24AA024virtualkey21980000virtualkey24AA024

The old trimmer has 3 legs, and the replacement 2.
Since the two holes near PCB edge are both ground, you will use only one of them



The failure mode draws extra current when the crystal oscillator stops.
Phase detector in IC 502 hangs with both outputs low, which draws
lots of current off Q302, pulling it low.
Resistor R304 1.2K then cooks. Original is only 1/4W. If damaged, replace with 1/2W or 1W.
I don't know if 1W resistor leads will fit in PCB holes.

My R304 was charred. I only had a 1/2W 1.1K in my parts box, but it measured 1.2K so I used it.
You'll have to remove top cover and unscrew the huge asymmetrical charge PCB to access it.


Now adjust trimmer cap; look at IC 502 (nearby TC9147BP) pin2 with a scope as you adjust for
maximum amplitude. If you have a clumsy high capacitance probe, you can probe through a 100K or so resistor.
Use a wooden screwdriver. Really. OK, so you think you're smarter than I am, and are using a metal screwdriver anyway.
At least wrap tape on the shaft like I did because you're going to ground it against the frame accidentally.

If you're a scopeless dork, you'll probably try using an AC voltmeter through a large resistor to find max while adjusting.

Your tuner is now fixed.

This tuner runs hot. I suspect the power supply was not designed for the extra card Carver added
for his asymmetrical whatever. I don't use multipath reduction as it destroys stereo separation.
Regular noise reduction works great.
I forgot what a great sounding tuner this is.

 
One other thing... I had a problem with two separate Carver 2000 receivers with bad tuner sections and displays. The cap and IC described above were not the problem. It turned out to be some small electrolytic caps on the display board that were essentially shorted.

Good luck!
 
txturbo said:
This tuner runs hot. I suspect the power supply was not designed for the extra card Carver added
for his asymmetrical whatever.
Click to expand...

Resurrecting an old thread, guys :)

I got two of these TX-11 tuners and I got them both to work. One of them, I recapped the power supply and replaced the 22 ohm 2W power resistor with a new 3W wirewound. That resistor heats up to 200-210 deg F (93-100 deg C) in normal use.

That seems a bit excessive? The post above says these tuners run hot though. My question is, how hot is normal?

The data sheet states "Maximum permissible hot spot temperature is 275 deg C" (Vishay PAC series).

Other than that resistor and the 2SD330 power transistor, which runs about 140 deg F at the heatsink, all other PS components run near room temperature.

If anyone out there still owns a healthy TX-11, I would appreciate knowing how hot they are supposed to run in normal operation. Thank you in advance!
 
Granted, this is old, but I just worked on a TX-11 with this exact problem. The multiplex (LA-3381 chip) section was down, and power into it was reading low, and most pins were at zero or also very low. The first candidate was C303 (100uF/16v) that is on pin 1 (Vcc) of the chip, just beyind a 150 ohm dropping resistor, which if shorted would have caused this. No joy. Further review led me to C312 (470uF/16v) from pin 15 to ground, which is part of the internal power stuff in the chip, and it had a hard short to ground. I replaced it, and all is looking good now . . .

Hopefully, anyine else searching may find this useful.

(Interestingly, I just refurbed a Carver C2 or similar vintage, and also found a 470uF/16v shorted to ground . . . Perhaps Carver had a particularly bad batch of those . . .)
 
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