robyn 520d

[galaxy]

i have a robyn 520d with a 858 pll. pcb# pc 176ab, i changed in the radio tr 4, tr 5 and ic 1. the receive is still sounds a little weak. someone came to close to my 20 with his amp on. Is there anything i can change in the radio to get stronger receive. the output is ok. am is weak receive, ssb is weak recevie. I would appreciate if someone can please give me a hand with this radio. thank you, galaxy

[Rick]

Check the alignment of the receiver, you will need an RF signal generator. It is very difficult to find a fault in the receiver if it is out of alignment.

Rick.

[ramblingman]

hello.it sounds to me like,one of your receiver front-end overload diodes have shorted,or opened up.check d-1 and d-2,for shorts or open conditions.you say your friend keyed up close to your 20 with a power amp on.this happens sometimes,it shorts out the front-end rf overload diodes.lift one lead of d-1,and d-2 out of circuit and check with your v.o.m.ill bet youll find one or both of them either shorted or open.d-1 and d-2 are off the base of tr-4 and tr-5.which are the rf amps.but you say youve already changed these right.but if you havent changed out d-1 and d-2 the voltage will drop like a rock and cause a weak or no recieve symptom.good luck with your radio....ramblingman

[ramblingman]

hello once again.forgot to mention,something else that might help you out.go to dxzone.com and go to the cobra service info. section and loook under the cobra 139 xlr,and pull up the schematic.the cobra 139 xlr has the same pcb as your radio the pc176ab.look in the area of tr-4 and tr-5 at the assc. caps and resistors also.

[galaxy]

thank you rick& ramblingman for your fast reply. i need to know the part # for d 1,d2. i dont have the sams photofact for this radio. galaxy

[ramblingman]

hi,according to the schematic the numbers for d-1 and d-2 are 1s2473.there might be an substitute that will work.you should be able to go to nte cross reference,dont recall the web site off hand.but i beleive you can find it throught dxzone.com

[Rick]

Diodes D1 and D2 can be replaced by 1N4148 or 1N914 or MA150 as there are only a general purpose 75ma 200 volt, but I think you are barking up the wrong tree, as D1 and D2 are not overload or front-end protections diodes, the protection in this radio is derived by FET2, TR11 and TR4. The easy way to check the front-end is the lift the collector of TR4 and if all is ok then the fault is if the AGC which is what controls the front-end.

Rick.

[galaxy]

Thank you,so much, Rick and Ramblingman. for your help. the radio receive works great... Know i noticed that the channel display is working. Both didgits are not on. I would apprecite if you can help me with this. galaxy

[ramblingman]

hello once again,well the display,is tricky to change out.but you can do it. just have to be real careful,and not burn your patterns into when your desoldering the old one.i have just resoldered them,and sometimes that will fix your problem with the display.if not if youve got a old radio laying around that dont work.rob the display out of it.if youll becareful unsoldering it,it should be fine.......ramblingman

[galaxy]

let me Thank you again.now the receive works and my channel display lites up! NOW on transmit my audio sounds to tinny. this radio is 25 years old. I know that the capacitors can dry out. can anyone tell me what capacitors to change to get it to sound bassy and to get loud audio. galaxy

[ramblingman]

hi there,let me check out the schematic,and ill get back too you soon.

[ramblingman]

hi there,sounds like youll need to change your bypass capacitors.try c72,c73,c74,c75.these are your coupling capacitors between our low pass filter and mic amp tr-20,they roll off the higher frequncy to ground via c73.your radio has a speech processor built in.oh. the glory of the good ole days...............ramblinman