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Lafayetts Telstat 140 SSB now just low power

Well i received brand new finals HG 1969 and 2sc2166.

I installed in radio and same low SSB power and little swing on AM.

Actually about 2 watts less on sideband 6 watts.

Am about 5 watts and peak to 6 watts.

Saying Ah on ssb i get about 3 watts and if i whistle i get about 8 watts max.

I guess i will have to give up for a while and work on something else.
 
here is an update on this ssb 140 telsat.
I have run the radio on the 12v plug and all seems good 5 watt AM swings to about 10 watts and ssb about 13 watts.

When run on AC I get about 4 watts Am very little swing and ssb about 6-8 watts max.

I checked the Ac power supply and its dropping about 2 volts during transmit. I checked the power regulator and dropping there also.
So next the AC out of the transformer and loosing about 2 volts about 21v Ac to 19v AC which makes the dc voltage drop about 2-3 volts also
I think the transformer is bad I replaced the 2 filter caps and still same problem and the regulator seems to be working properly.

I checked the 4 diodes and all good replaced the 2 electro caps got same results 2v drop, go back to dc v in and all is ok.

I dont think i will be able to find a new transformer so is there a small power supply i can install in the radio plenty of room if transformer is removed.3Screenshot_1.jpgpws 140.jpg
 
It's almost never the transformer. That component tends to be a go/no-go proposition. A "partial" fault almost never happens. The unregulated voltage you measured sounds about right. The voltage regulator is failing to hold the output steady. Question is why? An oscilloscope is a handy tool for troubleshooting this kind of issue. The rectifier ripple can provide a hint about who to blame. Can't see that with just a meter.

How much current does the radio draw from the external supply? If the final bias is turned too high, this causes excess current drain in transmit, and shortens the life of the final transistor. If the radio draws no more than 3 Amps in transmit on the external supply, this is not the cause.

Back before we started replacing this type power supply with chinesium "brick" switchmode supplies the routine was to check both zener diodes and replace all the electrolytic capacitors in the supply. We can no longer justify the labor cost to fix the factory power supply when a switchmode replacement costs the customer less than fixing the old DC supply. Both zener diodes and all 3 transistors should pass a proper test just to be sure. Filter caps, the two zeners and three transistors are pretty much the whole lineup of possible culprits.

73


73
 
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nomadradio said:
It's almost never the transformer. That component tends to be a go/no-go proposition. A "partial" fault almost never happens. The unregulated voltage you measured sounds about right. The voltage regulator is failing to hold the output steady. Question is why? An oscilloscope is a handy tool for troubleshooting this kind of issue. The rectifier ripple can provide a hint about who to blame. Can't see that with just a meter.

How much current does the radio draw from the external supply? If the final bias is turned too high, this causes excess current drain in transmit, and shortens the life of the final transistor. If the radio draws no more than 3 Amps in transmit on the external supply, this is not the cause.

Back before we started replacing this type power supply with chinesium "brick" switchmode supplies the routine was to check both zener diodes and replace all the electrolytic capacitors in the supply. We can no longer justify the labor cost to fix the factory power supply when a switchmode replacement costs the customer less than fixing the old DC supply. Both zener diodes and all 3 transistors should pass a proper test just to be sure. Filter caps, the two zeners and three transistors are pretty much the whole lineup of possible culprits.

73


73
Click to expand...
I replaced the 2 caps and still the same results. I will check the regulator again or replace and also the zener diode. Will also replace the D525 regulator
 
I replaced the regulator 2sD525 Q3 and still same results
On to ordering the 2 zener ZD1 and Zd2 And Q1 and Q2
I checked the resistors and all seem within specs.

Something is draining about 2 volts and as I mentioned the transformer is also dropping about 2 volts AC when keying mic on AM and SSB
 
Techno1 said:
I tried and still low power Radio is all set adjusted to factory spec Im waiting for some HG final replacements to see if its a final even though they check fine.
Seems like I stated low audio into the ssb carrier or maybe be a electro cap shorted to ground. that will be my next step checking voltages. I will also try a video to post here later that will be much better to explain.
And radio receives fine and transmits on frequency just low output ssb power
Click to expand...
Were the driver and final original. or....???
 
The current drain of the radio can't be measured easily using the internal power supply. But putting your meter on the 10-Amp DC hookup and inserting it into the positive wire of an external DC supply might be informative. If the radio is drawing excess current, that alone might be causing the voltage drop. Should 3 Amps or less with modulation.

73
 

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