| Author |
Message |
    
Jake
| | Posted on Wednesday, November 27, 2002 - 11:13 am: | 
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About 5or6 post ago If you recall my radio had a 1watt dead key on USB/LSB I adjusted vr7 and vr11, it reduced the carier 2or3 needles with. now i've noticed when you "turn" the switch to USB or LSB the resistor in the right rear R243 gets blistering HOT and of course the carier has gone up to 3.5 watts. The radio is an old Saturn for example vr12,13 and most of the resistors below them were not installed from the factory,the radio has a diod (swing kit) 742 regulatorand 2 resistors in the modulation section have ben changed to 2.2K and that is the exent of the MODS. would think something is getting ready to go bad. I'm asking for your help again, any suggestions would be appreciated |
307
| | Posted on Wednesday, November 27, 2002 - 10:03 pm: |
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Hi Jake , After looking at the schematics and the R-243 getting hot , I am all most positive the AM Power Regulator is shorted hard enough through some defective component to allow 12 volts at the final in the SSB mode. That is going to be rough...
307 |
2600
| | Posted on Thursday, November 28, 2002 - 1:44 am: |
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For starters, L27 and L28 are still set wrong. This is where your carrier on SSB is coming from. The fact that VR7 reduced the SSB carrier confirms that. This is NOT what VR11 is there for. Until the carrier has been eliminated from SSB, VR11 can't be set the right way, with NO drive in SSB transmit.
Unless you have 1) a counter that can be tapped into the test point in the radio, or 2) a short-wave or ham receiver with an EXTREMELY accurate frequency display, there is no good way to set L27 and L28.
R243 should run hot, but that's why they used a 1-Watt rated resistor there. If the radio was used for SSB a LOT, TR52 (2SD471) may be bad. One side of R243 is ground. The other end should show 6 or 7 volts DC when USB or LSB mode is selected. More than that will overheat it. I'm also beginning to wonder if the 9-volt regulator output is running too high. This causes all manner of puzzling problems when it happens. Find the audio power amp chip TA7222. Bolted to the heat sink to the front of it is TR41, originally a 2SA473. Meter the center leg for no more than 9.5 Volts DC. If you have much more than that, or much less than 8.5 volts, trouble will follow.
If the AM transmit audio is really weak or muddy, the trouble with R243 may involve other parts back in that corner.
73 |
307
| | Posted on Thursday, November 28, 2002 - 3:39 pm: |
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Wow , 2600 , never thought of the SSB Frequency being off , that would make sense. I still think that the 12 volt source is hitting the AM Power regulator. R243 should be hot , however the way I took it was burning hot..
307 |
Ss8541
| | Posted on Thursday, November 28, 2002 - 5:58 pm: |
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here is a question, how does it rx in usb and lsb? if l27 and l28 are set so far off that they are giving a slight carrier then you should not be able to understand rxed ssb signals. even if the 10.6925 and 10.6975 offsets are off because of improper tuning of l27 and l28, there still should not be a carrier(if bm is balanced it will null the carriers out), unless the tuning is so far off that the xtal is going into a weird oscillation. i'm not saying it can't happen because it can happen, but before you jump all over this being the case, you need to verify it the best way you can. if you are rxing ssb signals fine then l27 and l28 are not way out of whack and there -has- to be a problem in the balanced modulator area(like tr31 being slightly biased on or even very leaky, which in either case would pull pin 1 of the bm down making it unbalanced).
also the am mod/vreg delivers the full dc supply(12-14v) to the finals and driver during normal and proper operation. so even if the vreg is shorted, this would have nothing to do with your carrier. that is what r243 along with tr52 do. they pull down the base of the am mod/vreg so that it will be biased on hard and pass the full(or nearly full) dc supply voltage to the finals and driver.
i would suspect that quite a few areas of this radio have been tampered with by someone who has no business taking the lid off of a radio(even if they claim to be in business as a radio repair facility). you mentioned changed resistors in the mod amp area. there are other associated resistors in this area that could have an effect on r243/tr52 if they are changed. changing of components, working on areas while power is on, or even crappy work could have caused damage to the bm area giving your slight carrier in ssb. or like 2600 suggested the improper tuning of l27/28(from lack of knowledge about these radios) could be your problem there.
i'm not being smart with this, but without the proper equipment and working knowledge of these radios, you will never get this worked out yourself. it would take a competent tech less time to find your problems and fix them than the time spent on the forum trying to find just one of your many problems that this radio has. |
2600
| | Posted on Sunday, December 01, 2002 - 2:34 am: |
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Rock on, Richard.
Somebody on the web is suggesting that the USB/LSB carrier trimmers be set for "max wattmeter". Like most frivolous rumors, this one has been getting around. I think that's what his local "scewdriver expert" has been doing. I remember an older post that said other radios in his neighborhood acquired this same bad habit after a visit to Mr. Screwdriver. Straightening this out takes more than just an inline frequency counter with two coax sockets on the back. If you have access to a fancy ham radio that will tune 10.695 MHz on receive, tune in the Saturn's internal carrier, and set the slugs for "zero beat" with the ham receiver set to 10.6925 on USB and 10.6975 on LSB. I prefer the "receiver" method. It's quicker than waiting for a counter display to settle down after you twist the slug.
A counter with a probe, or a ham transceiver with an ACCURATE digital readout. Think of what happened when cars stopped using mechanical points in the distributor. You could set mechanical points without a strobe light. An electronic distributor REQUIRES one. You just can't set timing without it nowadays. Just think of the counter-with-probe or digital readout receiver as a timing light. L27 and L28 aren't that tough to set, but without either tool, you just can't.
One little quibble. The SSB filter is wide enough on this radio that SSB can be "understood" with the carrier frequency set well to one side of where it should be. Receiver audio quality ALONE won't be a conclusive test, I don't think. Even with the receiver carrier set dead center in the passband, SSB audio will be legible, if a bit tubby sounding.
73 |
307
| | Posted on Sunday, December 01, 2002 - 3:04 pm: |
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Jake , I really want to see what the trouble is with this rig , It won't cost you anything if you send it down and I will fix it..email me at tech307@copperelectronics.com if you are interested.
I had one a few years back that had this type trouble. If I recall it was an oscillator problem , I can't zero in on how I fixed it but I would like the challenge...
307 |
Ss8541
| | Posted on Sunday, December 01, 2002 - 7:45 pm: |
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2600, you are correct that the 10.695 filter in the ssb chain is wide enough to use the clarifier to offset the the 10.695if +/- so that it will mix with the 'ut of alignment'carrier osc offset for proper demodulation(on frequency). i should have made it clear that i meant with the clarifier straight up(and this is ASSuming that the vco is aligned) that he shouldn't be able to understand ssb signals. but we both know how many techs out there do 'by ear' freq alignments which leave both the vco and carrier osc off freq.
i'm sure that the whole radio is out of alignment(and more than just a little). but i really think that something in the bm area is causing his carrier in ssb. unless the carrier osc area is more than just out of alignment(even way out of alignment), there should not be any carrier. the bm, if balanced, should null out -any- carrier in this range. if it is -way- out of alignment he should have reduced power(the 10.695 filter will choke the off freq output if it is this far out of whack) with modulation. |
2600
| | Posted on Monday, December 02, 2002 - 11:15 pm: |
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I vote for 307 getting the job. At that price, how can Jake lose? There is another version of this problem we call "Truck Stop Super-Receive". Some poor fella reads the instructions to turn JUST three slugs to peak transmit power, and figures maybe turning some of the other ones will help, too. He has a tunnel-vision lock on the wattmeter needle while twisting every slug, one-by-one. No attention to where it WAS set, mind you, he wasn't looking at THAT. Just twist, shrug, and move on to the next one. The customer reports "Sure brought that pesky noise level down, but I can't hear 'em much further'n two miles, even if he's got a kicker." Sure enough, every receiver adjustment is nowhere NEAR a peak. Ya just can't align a receiver with a wattmeter. Heck, adjusting the transmitter with JUST a meter is a lot like playing pin-the-tail-on-the-donkey. You're bound to score now and again, but only by accident. If "Mr. Screwdriver" doesn't have a 'scope to SEE what comes out of the radio, he's just a ..... Well, never mind.
Still, I'll be curious to hear if I was right, if 307 gets to look inside it.
73 |
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