Seeing as I still have some time on my hands waiting for parts and gainfull employment. I started recapping my 142 .... All went well untill I got to a place where I had to pull a cap to ID it, after removal it read C108 with no plus mark so I looked it up the B O M and it says 0.022 uf 50v mylar .... NICE ... I just pulled out a 0.47 uf 50v electrolytic, made a note of it and moved on and boom it happened again pulled a 47 uf 10v electrolytic and found C79 no plus mark, B O M says its supposed to be a 15pf 50v ceramic ..... Interesting. Anybody here have any idea why this was done, other than a hack attack, seemed to receive good, never made a contact with this radio but judging from my surrounding area that's not too surprising .... I've researched and cant find a logical reason for these caps to be where they are, someones screw up is the only thought I can come up with. Anyway have had this radio for a while but have kept the 135 in use.
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Cobra 142GTL recap
- Thread starter HighPlainsDrifter$
- Start date
Looking at the schematics C79 should be a .1uf and C108 .022uf. The parts list shows C79 as a .1uf mylar and C108 as a .022uf mylar. The parts list also shows C79 again as a 15pf ceramic. It seems that there are mistakes in the parts list. I would say to go by the schematics.
I agree, the schematic is the best reference. I am no electronic engineer but I do know how to solder, how to replace parts and how to follow instruction. I guess my biggest question is why would someone take out a mylar and replace it with a polar electrolytic ... is there some secret in doing this or just a bonehead mistake? I have not gotten into modding radios simply because of things like this .... someone says do this so people do it. I have seen a modulation mod for this radio saying cut R104 but it does not say what it does for modulation it just says do it .... I'm leary. I like to know what the outcome would be before I just do it ... if you know what I mean. This particular radio is in excellent, close to pristine physical condition I would hate to ruin it, burn it down or be looking for parts that are now made of unobtainium.
Best thing would be to find someone with a 142 and have them look inside and see what caps. are in the in question positions. I have seen factory radios where the parts are not what the silk screen says. Example a cap. near the back of a 148 GTL.
I do like that idea but in this little town of 3800 souls in the middle of nowhere I think I'm the only one that's into 11 meter .... excepting a few kids with radios in their pickups (more power to em). When I put up the Maco V58 I think half the town drove by to see what I was up to, the other half sat at home and was waiting for the rumors. LOL I will take a couple pics maybe someone here has a good working 142 that will compare it with theirs.
Below is the parts list from a 140GTL-essentially the same chassis.
http://www.cbtricks.com/radios/cobra/140gtl/graphics/cobra_140gtl_om_parts_list.pdf
Parts list from the 142GTL
http://www.cbtricks.com/radios/cobra/142gtl/graphics/cobra_142gtl_om_parts_list.pdf
Service and Parts Manual for R/S TRC450
http://www.cbtricks.com/radios/realistic/trc_450/graphics/realistic_trc_450_sm.pdf
These are all similar chassis and should help you get where you're going.
73
David
http://www.cbtricks.com/radios/cobra/140gtl/graphics/cobra_140gtl_om_parts_list.pdf
Parts list from the 142GTL
http://www.cbtricks.com/radios/cobra/142gtl/graphics/cobra_142gtl_om_parts_list.pdf
Service and Parts Manual for R/S TRC450
http://www.cbtricks.com/radios/realistic/trc_450/graphics/realistic_trc_450_sm.pdf
These are all similar chassis and should help you get where you're going.
73
David
Thank You, Very enlightening. I have the copies of the 142 info from CB Tricks but was unaware of the TRC 450 .... after looking at it the values of the electrolytics for C79 and C108 in the 450 those are exactly what I removed from the 142, makes me wonder why the difference from Cobra to Realistic and I might ought to stick with the Cobra mylars and values ??? It is obvious to me someone has been in this radio before, roughly a third of the electrolytics have been changed from the original Uniden to Delcon korea ... possibly the person who was in there only had access to the Realistic service manual and went by that B O M not realizing that Cobra did something different .... I dont know ... I am open to suggestion at this point. Are things going to act and react correctly changing from Cobra mylars to Realistic electrolytics I personally don't know what the differences would amount to. I did notice on the TRC 450 board pictures that the polarity was marked so that simplifies thing a little because I did not pay attention when I pulled the caps expecting to find a marking on the board ,,, MY bad. Those 2 caps are the only things I've found not to follow the Cobra schematic. Sorry for the ramble, thinking out loud sorta.
Maybe its an either or situation here ... I dont know
Maybe its an either or situation here ... I dont know
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I have a taiwan 142 that hs not been messed with capacitor wise. If you want to know what is in it, let me know.
Tony
Tony
Yes most definitely .... I would. Mine is also a tiawan and a 1978 judging from the ICs
Thank You
Well, I rolled the dice and and replaced C79 and C108 with fresh electrolytics .... still not sure if that is right according to Hoyle but that's what was in there. Fired it up and made contact with 167 in Ontario CA. on 38LSB, seem to be smokin again ... atleast for now. Don't know if hes on here but if he is, nice talking with you. Barefoot 142GTL
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Well here I am tinkering again, figured since I got sorta caught up again I would do the TSB 1226 on this 142gtl went to replace D60 with an 18V zener and found that there is no D60, I mean the place is there but it appears that some where along the line it has been removed. So I assume I should put a zener in there ... Yes? Also I have a couple of options here #1 an 18V 600W and #2 18V 1.3 W. Which would be the best idea? I am not sure the radio works well as it is but ...... any advise???
If you use the ORIGINAL power supply, being the linear type and for the age it is,
Yes, please continue to do the work and install the 18V zener - as a measure of safety - along with a review and possible change of the power supply to Main PCB board - install an In-line fuse of 3.5 to 4A - 250V rating IN-LINE with the power wire - to protect your investment.
You cannot guarantee the voltage arriving to the radio is going to be 120 volts or LESS
You also cannot guarantee the DC input voltage and external Power Cord will be properly fused...
Avoid the headaches and install that fuse at the power wires INPUT to the switch to reduce the chances of catastrophic failure.
Yes, please continue to do the work and install the 18V zener - as a measure of safety - along with a review and possible change of the power supply to Main PCB board - install an In-line fuse of 3.5 to 4A - 250V rating IN-LINE with the power wire - to protect your investment.
You cannot guarantee the voltage arriving to the radio is going to be 120 volts or LESS
You also cannot guarantee the DC input voltage and external Power Cord will be properly fused...
Avoid the headaches and install that fuse at the power wires INPUT to the switch to reduce the chances of catastrophic failure.
OK, I will do that .... sounds like good advice. Also concerning the the zeners, is using a 600W better than using a 1.3W ..... is it like increasing the V rating for capacitors,
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