galaxy DX-88hml low ssb power am ok.

[speedracer6g]

I got another pain in the neck radio. This radio works well on am but on ssb it is not as strong I am only getting about 12 watts avg from this radio on ssb. I am getting 25 watts avg on am so I sould see as least that on am. I adjusted the alc and it only makes a two watt difference. I had to replace tr51 because it shorted. When it whent bad the radio dk 40 watts and sideband worked. Now that i replaced tr51 am is fine again and ssb is back to its 12 watt power again. I checked tr52 the ssb switch and it was fine so i replaced it just to be safe. I checked the voltages after and before installing the replacement and they go as follows:

AM-------------------SSB
E 0V.------------- E 6.6V
B 13.1V---------- B 12.7V
C 0V------------- C 7.4V

Anyone have any ideas?

Mike

[marveylus22]

have you tried to adjust VR12?

[speedracer6g]

yes it only changes it by about two watts. I Usually see about 40+

MIKE

[Rick]

What is the base voltage is SSB TX of TR51 with full modulation?
What is the collector voltage is SSB TX of TR51 with full modulation?
What is the voltage drop across TR51 in SSB TX with full modulation?

[speedracer6g]

What is the base voltage is SSB TX of TR51 with full modulation?
Base voltage with full modulation on SSB is 11.7 volts.

What is the collector voltage is SSB TX of TR51 with full modulation?
Collector voltage with full modulation on SSB is 7.28

What is the voltage drop across TR51 in SSB TX with full modulation?

EC DROP IS 5.46 VOLTS
CB DROP IS 4.2 VOLTS
BE DROP IS 1.2 VOLTS

THANKS RICK.

MIKE

[speedracer6g]

I noticed that hi and low power changes nothing on SSB. It stays the same on either setting. Also low power SSB works fine but high power SSB has spurrious emmissions almost like am ontop of ssb.

thanks,

MIKE

[Rick]

Maybe R243 has gone HR, check the voltage on the base, collector and emitter of TR52, the voltage in SSB should be base 7.75 vdc collector 13.65 vdc emitter 7.05 vdc.

[speedracer6g]

those voltages look good as well as R243 it is also checking out fine. when i checked voltages on tr52 on ssb i recorded B 7.6v C 13.1 E 7.06.

MIKE

[Rick]

There is something wrong you say the Collector voltage of TR52 is 13.10, it needs to be 13.65 to 13.70, or the pass transistor will not turn fully on.

Try this unsolder the pass transistor and solder a link from the emitter to the collector, now see if you have full power on SSB. CAUTION do not use the radio in AM or FM while the pass transistor is by-passed

Also check the current being used by the PA stage in SSB with full modulation.

[speedracer6g]

The pass transistor is tr52 correct?

MIKE

[Rick]

No the pass transistor is TR51.

[speedracer6g]

oh sorry I no what you mean now. thanks

MIKE

[speedracer6g]

I did put a jumper from emitter to collector of tr51 and ssb is at full power now. I connected tr51 back into circuit and checked voltage with full modulation and i looks like i loose my voltage on the collector. It drops down to 7.6 volts on tx with modulation. hmmmm.

mike

[Rick]

If that is the case, then it looks like you are not turning the pass transistor fully on.

If you can give the voltages base, collector and emitter of TR49, 50, 51, 52, 53, and 54 in SSB TX with full modulation.

What is the R242 and R243 reading?

Remember that the pass transistor is a PNP, hence it base needs to go negative with respect to the emitter to turn on.
Therefore, if the emitter is at 13.80 which is the supply volts, then the base need to go negative to about 13.60 to 13.70 to turn full on.

A few years back a radio came in to me with low SSB power and after check it out I found that the two smoothing caps had gone low, hence no current when you need it.

[speedracer6g]

ok here goes.

TR49 B 7.5 C 11.5 E 7.35
TR50 B 11.5 C 7.3 E 11.75
TR51 B 11.75 C 7.3 E 12.95
TR52 B 7.0 C 11.6 E 7.0
TR53 B .85 C 7.8 E 1.8
TR54 B 0.0 C .5 E 0.0

R243 46.6 OHM
R241 9.7K

[speedracer6g]

where are the smoothing caps??

[Rick]

The smoothing caps are C194 and C195 (1000uf at 25 volt), I replace them with 2200uf at 25 volt.

The fault lies somewhere around TR49 as the base voltage is to low in SSB, the components which control TR49 is a feedback circuit, which is formed by R240, R241, and D91. C190 is the AM audio roll off cap but this can cause a fault if it is leaking.

Check R240, R241, C190, and D91 which maybe o/c
Check TR49 has it may have a base emitter leak, just replace it as it may not show up on a transistor test.

[speedracer6g]

Well i found the problem. I must of bought a bad batch of 2sb827 transistors. I went back to the 754 that was in it and it worked fine. So i installed a 827 that i knew was good and now everything is just fine. that is what i get for ordering from a guy in china. Lesson learned. I check the Hfe gain on my transistor tester compared to a one of my good ones and there is a differnce. thanks for all your help Rick.

MIKE