|
Post by 960 on Dec 16, 2007 4:44:40 GMT -5
My T240D has weak low level receive, local stations are fine but I get barely any static and far away signals are non existant.
I changed out all tubes with known good replacements. no improvement. I replaced a number of signal resistors (mostly 10K ohms) nothing. I also changed out all the .1uf oil caps too and no improvement.
T cannisters???
Any thoughts or if you had your radio have the same problem and you or your tech found the fix I would love to here it.
|
|
|
Post by Tombstone (R.I.P.) on Dec 16, 2007 9:00:53 GMT -5
Try aligning the receive if you can find the alignment instructions, maybe someone put the golden screwdriver to it and it's out of whack?
Tombstone
|
|
|
Post by spends2much on Jan 10, 2008 16:23:56 GMT -5
Sounds like you might of had it sitting to close to a tram lol!
|
|
|
Post by n9ydx64 on May 16, 2008 15:03:51 GMT -5
just pickup a Gemtronics GTX5000 it has same problem too. weak receive
|
|
|
Post by Tombstone (R.I.P.) on May 16, 2008 18:58:24 GMT -5
Do all of your radios have weak receive? Maybe the antenna is at fault?
Tombstone
|
|
|
Post by n9ydx64 on May 16, 2008 19:24:50 GMT -5
its the radio. i run hr2510 on the same antenna and hear 30 miles away. i just pickup radio from auction about week ago.
|
|
|
Post by captbarry on May 22, 2008 3:02:00 GMT -5
Man must be something going around cause I have power dropping off on Teaberry Model T and I have hardly used it since it was completely rebuilt! Getting ready to box it up and send it to the tube radio Dr. Will let you know. Capt. Barry
|
|
|
Post by pathfinder259 on Jun 12, 2008 20:05:56 GMT -5
HELLO,,Have you checked the tube sockets..They get worn on these old units..New tubes wont help if the sockets are worn. I have just cleaned the old sockets using contact cleaner or wd-40 Spray some in each socket,and put tube into and wiggle around. Then before powering it back up.Use some can air,and blow it out good.Sometimes you have to change the sockets out though. Good to check all the simple stuff first.Also clean the volume control with some contact cleaner.
|
|
|
Post by pathfinder259 on Jun 12, 2008 20:33:17 GMT -5
HELLO,,By the way i forget to mention.I have two of the yellow birds.One is in great shape,Loud audio,Great recieve. And i have one that has great recieve,but no tx.The relay clicks,but it wont keyup.good audio coming though p.a. on p.a. test..Just no tx.I just sit it to the side.I guess i need to get back on that repair..Also you all was talking about the radios you were having trouble with..All of these radios have exact same chassis..Robyn T-240d,Robyn 123b,Gemtronics gtx 5000 Teaberry model t..Chassis are the same.Just some good to know info.....
|
|
Sandbagger
Administrator/The Boss
Posts: 6,247
|
Post by Sandbagger on Jun 12, 2008 20:36:55 GMT -5
HELLO,,By the way i forget to mention.I have two of the yellow birds.One is in great shape,Loud audio,Great recieve. And i have one that has great recieve,but no tx.The relay clicks,but it wont keyup.good audio coming though p.a. on p.a. test..Just no tx.I just sit it to the side.I guess i need to get back on that repair..Also you all was talking about the radios you were having trouble with..All of these radios have exact same chassis..Robyn T-240d,Robyn 123b,Gemtronics gtx 5000 Teaberry model t..Chassis are the same.Just some good to know info..... Yep, and all made by Panasonic. Beware of the .1uF electrolytics. They like to pop off like firecrackers when they go bad.
|
|
|
Post by radioreddz on Jun 13, 2008 10:10:28 GMT -5
wow must be an inherent problem with these chassis. i posted the same question maybe a year ago about my GTX-5000 when i first power it up it TX & RX fine but after a while it get hot to the touch and every thing falls of TX & RX. sent it out to two different techs with no results. always get it back with the i see nothing wrong. i don't think they leave it on more then two minutes.
|
|
|
Post by 2600 on Jul 3, 2008 1:39:44 GMT -5
Well, if the "customer complaint" part of the repair ticket says "Receiver goes out after a one-hour warmup" or some such, this makes it sound as if they'd rather not fool with it.
But you won't be able to make any voltmeter measurements that point you to the trouble UNTIL it gets hot enough to malfunction.
There are enough old-technology carbon-composition resistors in that radio to cause this kind of trouble. When they go bad, they can become temperature-sensitive.
Tubes can do this, but it's not that common. More than once, I've seen a half-Watt resistor that got overheated and discolored from a tube that went bad. When the bad tube was replaced, everything worked. Until the tempreature started to rise. The resistor didn't get totally clobbered, but turned it into a "temperature sensing" resistor. Works at room temp, but not at operating temp.
The calibrated eyeball is your number-one tool to find this problem. A bum resistor may or may not LOOK bad, but if you see the color of a resistor's body that's darker near the center, this is a clue the thing has overheated in the past. And if the color bands are faded or scorched black, this means you can no longer read the part's resistance value this way. If you find one of those, it's off to the schematic to identify it's correct value from the parts listing.
Now and again, looking inside a tube radio, I'll find a resistor that has clearly been replaced, but has the wrong value. Say, if the original was yellow-violet-orange, or 47k, I would find a 47-ohm. A black third band, not the orange that SHOULD be there. Some impatient schmuck read the burned-black third band as he saw it. Not as it was before it burned from orange to black...
Yes, seeing is believing, but ONLY when it agrees with the schematic.
73
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jul 7, 2008 21:36:20 GMT -5
I have a Yellow Bird with the same problem. No receive. It is a problem with this chassis. Many people like Sandbagger and Nomad have led me to those resistors. I have recapped the radio, but have not done the resistors yet, as house projects got in the way.
And Dave, in honor of you, man in Florida sent me a Robyn Green Machine with one of those caps that popped. That will be an easy fix.
|
|
Sandbagger
Administrator/The Boss
Posts: 6,247
|
Post by Sandbagger on Jul 8, 2008 7:02:13 GMT -5
I have a Yellow Bird with the same problem. No receive. It is a problem with this chassis. Many people like Sandbagger and Nomad have led me to those resistors. I have recapped the radio, but have not done the resistors yet, as house projects got in the way. And Dave, in honor of you, man in Florida sent me a Robyn Green Machine with one of those caps that popped. That will be an easy fix. Ah yes, the infamous .1uF firecracker. I've seen more of them that popped than haven't when they get to a certain age in those Panasonic-made radios. Usually it's the one that feeds the -82V supply.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Aug 25, 2008 7:43:31 GMT -5
I have found something quirky with my no receive. If I push the CB/PA switch ever so slightly (and hold it there), the receive comes back. When I let go, it's gone. I sprayed the switch, with no luck. I am now going to attempt to jumper the wires and eliminate the switch.
The other the problem is the dead key comes and goes. I 'll work on the receive first.
|
|
Sandbagger
Administrator/The Boss
Posts: 6,247
|
Post by Sandbagger on Aug 25, 2008 8:16:08 GMT -5
I have found something quirky with my no receive. If I push the CB/PA switch ever so slightly (and hold it there), the receive comes back. When I let go, it's gone. I sprayed the switch, with no luck. I am now going to attempt to jumper the wires and eliminate the switch. The other the problem is the dead key comes and goes. I 'll work on the receive first. Sounds like you found a bad switch. Jumping it out is a good way to verify it. Just don't flip the switch to PA while it's jumped out in the CB position.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Aug 25, 2008 22:12:58 GMT -5
Struck out on the switch. I pulled the wires to one of the poles to measure out the switch. It measured good in both CB and PA positions. The receive comes and goes. I was on here when I heard the radio just start receiving. When I ran in there to look at it, it was gone. I was trying to see if the S meter was moving with the receive, but didn't get in there on time.
|
|
|
Post by BionicChicken on Aug 26, 2008 6:36:30 GMT -5
If the CB/PA switch is bad you will lose both receive and transmit. That could be the answer to both of your problems. Just bypass the switch all together (ie: remove and tie wires together that need to be and isolate the ones that don't) if you are not going to use the PA function and go from there. You can always replace it later on.
BC
|
|
Sandbagger
Administrator/The Boss
Posts: 6,247
|
Post by Sandbagger on Aug 26, 2008 7:21:18 GMT -5
Struck out on the switch. I pulled the wires to one of the poles to measure out the switch. It measured good in both CB and PA positions. The receive comes and goes. I was on here when I heard the radio just start receiving. When I ran in there to look at it, it was gone. I was trying to see if the S meter was moving with the receive, but didn't get in there on time. Did you actually jump out the switch? It's possible that there's enough resistance in the contacts to create a problem. But it's clear in any case that you have some sort of intermittent in there if the receive comes and goes. If it's not the PA/CB switch, there are a multitude of mechanical and electronic parts that can cause an intermittent. Tube sockets can become oxidized, the contacts can lose temper and cause problems. Wiggling the tubes while the rig's on can sometimes expose this kind of problem. Look for a cold solder joint on the tie points, especially if the rig has been services previously. Also, carbon resistors can change value and become heat sensitive after 100,000 miles of steady current draw. Those small value electrolytic caps can either short or open or become leaky which can cause a supply voltage to disappear or drop too low to work properly.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Aug 26, 2008 7:29:36 GMT -5
I didn't jump out the switch, but I did measure the resistance. All was fine. Most of the resitors are not carbon. There are only a couple that are. All elecrtolytics have been replaced. I did try the tube wiggle and also tried replacing them one at a time with tubes from the T-123B. Solder joints checked out.
I think there is a problem in the squelch circuit, as I cannot get the squelch to work. Also, I have verified that the S meter is non-functional when the receive comes back. It did work when I had transmit. Will go back at it tonight.
|
|
Sandbagger
Administrator/The Boss
Posts: 6,247
|
Post by Sandbagger on Aug 26, 2008 10:32:08 GMT -5
I didn't jump out the switch, but I did measure the resistance. All was fine. Most of the resitors are not carbon. There are only a couple that are. All elecrtolytics have been replaced. I did try the tube wiggle and also tried replacing them one at a time with tubes from the T-123B. Solder joints checked out. I think there is a problem in the squelch circuit, as I cannot get the squelch to work. Also, I have verified that the S meter is non-functional when the receive comes back. It did work when I had transmit. Will go back at it tonight. If the squelch doesn't work, check your -82V supply. There are a couple of those firecracker .1uF's in there and that supply feeds the squelch as well as cutting off the transmit final on receive to keep it from taking off into oscillation (The problem my Comstat had).
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Aug 26, 2008 17:58:09 GMT -5
I replaced the .1 firecrackers with poly film caps. I will check the supply. I appears this chassis is know for it's receive loss. But the weird thing is that there doesn't seem to be one common failure.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Aug 26, 2008 21:43:28 GMT -5
I checked and found 3 carbon resistors. 2 were way out of tolerance, and went higher as I put a soldering iron to them. The 3rd was fine. I will replace all three. I noticed when I key the mic, as soon as I unkey, I hear the receive for a split second. This one os going to drive me nuts.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Aug 27, 2008 21:57:35 GMT -5
Checked voltages, all look OK. Ho often do diodes fail in these things?
|
|
|
Post by Tombstone (R.I.P.) on Aug 28, 2008 14:56:19 GMT -5
I doubt that the problem is a diode unless it's broken and only sometimes making contact, the ones I've checked are either good or bad. I think you still have a resistor problem. I had a T240D that the receive would come and go and if you tapped the cover it would come back on. I found a cracked resistor and once it was replaced I had constant receive but I can't tell you exactly what one it was. With the radio upside down and the front facing you, on the lower right hand area you'll see a couple of transformers and a tube socket or two. The resistor that I found was in that area, I think on one of the transformers. With the radio powered up, antenna connected, just gently push on the resistors with a non cunductive tool like a heavy alignment tool. Please keep one hand in your pocket when doing this, I don't want to hear about you getting zapped. This is just a suggestion from experience but I hope it helps you.
Tombstone
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Aug 28, 2008 15:41:19 GMT -5
I have tried that (I think you had suggested it) tool knocking. What I found are most of the resistors are carbon film, and only 3 were carbon composite. None look discolored. I might have to try the tubes one more time. Very weird.
|
|
|
Post by Tombstone (R.I.P.) on Aug 29, 2008 16:08:03 GMT -5
Hmm....sounds to me like the hit and miss approach isn't working. I think it's time for a signal generator to be connected to the antenna connector. That way you can trace the signal from the radio's front end and find out where you're losing it.
Tombstone
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Aug 29, 2008 18:18:25 GMT -5
Yep. I tried the tubes again, with no luck. I think the signal generator is a plan.
|
|
Sandbagger
Administrator/The Boss
Posts: 6,247
|
Post by Sandbagger on Aug 29, 2008 19:48:49 GMT -5
Yep. I tried the tubes again, with no luck. I think the signal generator is a plan. Yes, that's what you'll have to do. Start at the I.F. and work your way back to the receive front end. set the generator for 455 Khz, and pump in somewhere in the neighborhood of 100mV just before the detector and slowly work your way back each stage, while dropping the generator output level to keep a good signal level. When you pass the mixer stages, you'll have the change frequency on the generator to correspond to the stage you're in. At some point you'll lose the signal, and that stage will be where the problem is.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Aug 29, 2008 21:53:47 GMT -5
Well, I found a 3pf coupling cap (C101) that feeds the input of the RF amp tube. It is not passing an AC signal. I pulled it and and tried with a 200KHz sine wave, and it doesn't go thru. And it's a ceramic disc, no less. Can't be that easy. I don't think I have one of that value. Can I use a .01uf just to test?
|
|