Galaxy 98vhp deadkey 250 watts on ssb???

[speedracer6g]

Galaxy 98vhp

motorola 2100b service monitor, scope, frequency counter, bird 43p meter, dosy tc3001-p meter, 75 amp power suply, simpson vom meter, digital multimeter, ect.

Am works fine, altough on at one time on low power it had no deadkey unless you turned up the rf power. that problem i have not been able to duplicate. The biggest problem is on SSB it will work fine when you first turn it on. then after a min. or so it will slowly start to show power until it reaches 250 watts. with no audio. I replaced the folowing components, q55, 54, 56 57, and r172 . i also remove the swing kit that was in it. the diode on r264. If anyone has had this problem or has an idea let me know. i am chasing my tail.

thanks,

MIKEY

[The Defpom]

I would be looking at the balanced modulator first (IC6), to make sure that it is filtering out the sidebands and only providing an audio carrier, and then go from there.

[speedracer6g]

I tried replacing IC6 and it still did the same thing. It is almost like a resistor is opening up or there is a bad cap somewhere in the balanced modulator circuit. I talked to galaxy tech and they had no answers. I will keep digging around ic6 to see what components are involved.

thanks,

Mike

[speedracer6g]

I checked the output of the balanced modulator IC6 pin 7 and it shows no carrier only audio when things are working properly. However when the radio quits working right i notice that carrier is showing up on pin 7 as well. I have tried to replace ic6 with no results.

MIKE

[The Defpom]

Then it is likely to be something around the BM, I would start by checking the power supplies and switching, Q34 does the switching, it may be leaky so it is not switching off properly, also check C149, C144, C146, C145 after that you will just have to check each resistor around the IC, R172, R174, R169, R170 (if present).

C150 and C147 are unlikely to be the problem, bt if nothing turns up after doing the others, then look at those too.

It is also possible that there is audio noise being generated, so if possible scope the audio input (pin 1) and check that it is noise free, as that could cause it to produce a carrier.

[speedracer6g]

thanks for the tips. I will recheck my supply voltages just to make sure. I think i did already but I will recheck to make sure. thanks again for your time and support.

MIKE

[speedracer6g]

I replaced C149, C144, C146, C145, R172, R174, R169, Q34, D57, AND R171. I checked pin one and there seems to be an oscillation the shows up when things go sour. I checked and the oscillation is present at R171. I was going to trace that to see if i could isolate where the noise is coming from. Any ideas let me know but in the meantime i will try to isolate the source.

thanks again,

Mike

[speedracer6g]

It appears to be an audio oscillation coming from the mic amp IC7. It is high enough frequency that it is inaudible. things are starting to make sense here finally. I just have to find out what is causing the audio problem now. aarrrgg.

MIKE

[speedracer6g]

I found the problem. There was a oscillation showing up on the output of ic7 after a minuit or two. Replaced ic7 njm4558. Works great. thanks for all your help. It was hard to find since it didnt affect the am side.

MIKE

[The Defpom]

Good to hear that you found the fault.