Yamaha TX-1000U No FM Signal
- Thread starter mea2112
- Start date
Would one of you great teachers mind explaining how I could go about jumpering to the front-end to check the PIN diodes?
Thanks.
D3 and D4 are under copper-colored shield I'm guessing. How do you get that dang cover off? Best (only?) way to short D3 to D4?
I am not sure exactly how to dis-assemble the shield cover since I do not have one nor have I serviced one in the past. Sometimes they are friction fitted, in some cases they are soldered. Use a jumper wire with some grabber clips on both ends to apply the short.
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Thanks. Power Supply test points measured -12V and +12.39V
Finally got the shield cover off. Internal A/B antenna parts appear to be undamaged.
On to the D3/D4 diodes. Man, they are tiny! Like 3/16"? My small grabber clips are too big to grab onto the anode/cathode. Any other suggestions?
Also, the point of shorting D3 and D4 is to bypass them or essentially remove them from the circuit right?
Finally got the shield cover off. Internal A/B antenna parts appear to be undamaged.
On to the D3/D4 diodes. Man, they are tiny! Like 3/16"? My small grabber clips are too big to grab onto the anode/cathode. Any other suggestions?
Also, the point of shorting D3 and D4 is to bypass them or essentially remove them from the circuit right?
With power off you can do a DMM diode test on those diodes to see if they measure okay. D1-8
need to get smaller grabber clips to get at the leads.
You can also access the diodes from the solder side of the pcb.
need to get smaller grabber clips to get at the leads.
You can also access the diodes from the solder side of the pcb.
That is correct. You do not know if the diodes are open, short or okay, have to check them out.
Time to revive this thread...
I have a TX-1000U with the same symptoms, and ran across this thread while looking for help.
After a while I put 2+2 together and realized that the TX-1000U that I acquired in a package deal from someone SW of Chicago a few years ago must be the same one discussed in this inconclusive thread.
The only difference is that while I can get at least 80% signal strength on the meter on AM, I get no sound whatsoever out of the tuner when connecting it to my SX-1050.
As mea2112 posted, I found all DC supply voltages to be correct, including the switched FM and AM rails.
As others suggested, I used the diode scale on my DMM to check D1-8 on the antenna switch. All seem to be OK. About 0.76V (IIRC) in one direction, and no reading in the other direction.
I ordered some adapters for the antenna connectors in case mine aren't making good contact.
Next time I work on it I will try jumpering across D3/4 and using the A input, as suggested, but don't expect that to work since the diodes seem good, and the +/- 12V are present.
Other suggestions are welcomed...
(I have a scope, but no generators.)
I have a TX-1000U with the same symptoms, and ran across this thread while looking for help.
After a while I put 2+2 together and realized that the TX-1000U that I acquired in a package deal from someone SW of Chicago a few years ago must be the same one discussed in this inconclusive thread.
The only difference is that while I can get at least 80% signal strength on the meter on AM, I get no sound whatsoever out of the tuner when connecting it to my SX-1050.
As mea2112 posted, I found all DC supply voltages to be correct, including the switched FM and AM rails.
As others suggested, I used the diode scale on my DMM to check D1-8 on the antenna switch. All seem to be OK. About 0.76V (IIRC) in one direction, and no reading in the other direction.
I ordered some adapters for the antenna connectors in case mine aren't making good contact.
Next time I work on it I will try jumpering across D3/4 and using the A input, as suggested, but don't expect that to work since the diodes seem good, and the +/- 12V are present.
Other suggestions are welcomed...
(I have a scope, but no generators.)
Did a little more digging today...
Even with around 40% signal strength indicated on the meter in AM, the mute signal is stuck on.
There is always +0.7V on the bases of muting transistors Q53-56, causing them to ground the audio outputs.
All the way back thru Q94, and D40 to U11 pin 22, the mute signal is stuck on.
At the U11 pin 22 source, the voltage is always +7.05V on AM (with or without good signal on meter), and +6.96V on FM (on which I still get no meter movement at all).
Does anyone know what U11 uses to determine if it should be muting the audio or not?
I'm guessing this becomes a parts unit if U11 itself is bad...?
I noticed one other odd thing on AM.
When I switch to AM there is initially no meter indication, but the meter wakes up as soon as I start adjusting the tuning knob.
On FM, I did temporarily install a short jumper from D3 Anode to D4 Cathode and connect my antenna to the A port, but still could not get any signal meter movement at all.
Even with around 40% signal strength indicated on the meter in AM, the mute signal is stuck on.
There is always +0.7V on the bases of muting transistors Q53-56, causing them to ground the audio outputs.
All the way back thru Q94, and D40 to U11 pin 22, the mute signal is stuck on.
At the U11 pin 22 source, the voltage is always +7.05V on AM (with or without good signal on meter), and +6.96V on FM (on which I still get no meter movement at all).
Does anyone know what U11 uses to determine if it should be muting the audio or not?
I'm guessing this becomes a parts unit if U11 itself is bad...?
I noticed one other odd thing on AM.
When I switch to AM there is initially no meter indication, but the meter wakes up as soon as I start adjusting the tuning knob.
On FM, I did temporarily install a short jumper from D3 Anode to D4 Cathode and connect my antenna to the A port, but still could not get any signal meter movement at all.
Thanks, tried looking but haven't found it yet...
Thanks again, but this old fart doesn't know how to use that link. When I click on it, I get a new window which is for composing an email from the Google account that I never use to the address of the link. Am I supposed to email them requesting access to the forum?
Sorry here is a better set of links
https://groups.io/g/FMtuners
Group Email Addresses
https://groups.io/g/FMtuners
Group Email Addresses
- Post: FMtuners@groups.io
- Subscribe: FMtuners+subscribe@groups.io
- Unsubscribe: FMtuners+unsubscribe@groups.io
- Group Owner: FMtuners+owner@groups.io
- Help: FMtuners+help@groups.io
