Spectra: Fuse Locations?

[Splat]

While installing my vhf Spectra today I believe my brother somehow shorted the radio before I installed a fuse on the mains. That's what I think happened since he simply plugged the power mains to the radio and I heard a spark. Now I get the dreaded Fail 01/90. I don't have the service manuals so could someone please tell me where the main fuse(s) are located on the boards? Hopefully that's all it is but with my luck probably not. Thanks.

[Jim202]

While installing my vhf Spectra today I believe my brother somehow shorted the radio before I installed a fuse on the mains. That's what I think happened since he simply plugged the power mains to the radio and I heard a spark. Now I get the dreaded Fail 01/90. I don't have the service manuals so could someone please tell me where the main fuse(s) are located on the boards? Hopefully that's all it is but with my luck probably not. Thanks.

First of all you need to provide just a hint of what you have.

Is this a dash mount or a trunk mount?

Is this a high powered unit or a mid powered unit?



All the radios use the high current + 12 volts DC power feed to the transmitter. It is fed with from a 15 Amp fuse to a 30 Amp fuse depending on the TX power rating through the heavy red wire from the battery to the radio. It must have power on the radio to make it power up correctly.

Then there is the control head power wiring. There should be both an orange and a green wire that normally have a 3 amp fuse in each. Again both wires need to have + 12 volts DC power at the radio.

At this point it is going to take a volt meter to track down the problem. Is there any chance that the heavy red and black wires were reversed when power was applied to the radio. There is a protection diode in the radio that is there for just this reason and it will blow the high current fuse. Also make sure the heavy black wire is ground.

Jim

[Splat]

First of all you need to provide just a hint of what you have.

Hey Jim. Thanks for responding. It's a mid-power dash mount converted to trunk mount. There is only a red wire going to the acc/connector off the A5 head which was ran to ign/switched power in the car.

At this point it is going to take a volt meter to track down the problem. Is there any chance that the heavy red and black wires were reversed when power was applied to the radio. There is a protection diode in the radio that is there for just this reason and it will blow the high current fuse. Also make sure the heavy black wire is ground.

I've been going over things with my Fluke meter. Is that protection diode the big sucker on the PA board next to where the red+ lead is soldered onto the board? That's passing 13v and from my testing around it appears the main power is ok. I also tested good continuity on that green axial lead fuse on the command board. PS, no the main leads were not reversed. My brother said he just went to plug the power plug onto the radio and it sparked. I know it could be anything. The joy of electronics. I'm trying to secure another head to try on it but that won't be any time soon.

[Splat]

Found the problem and it's time to disown my brother from the family.

I swapped out the mini uhf for a SO239 type connector on this Spectra a few days ago and I didn't have time to test it out. I hate those mini uhf's! I asked him to test it and I thought he did so but alas, the dumbass doesn't now remember testing it. I guess I'm the dumbass for not doing my own testing though, like I usually do. I desoldered the coax center conductor off the board and tested the radio and it now powers up fine. The weird thing is when I initially did the connector swap I removed the mini-uhf and its coax I checked continuity and found the coax's center conductor was shorting. I thought that's the way the circuit went because some amplifiers do ground the conductor on receive. Well, apparently something's not right now. The big question is.... is the center conductor going to the antenna connector supposed to be grounded/shorted when the radio has no power applied? I don't have the service manual for the Spectra and can't find it online so I'm at a loss until somehow informs me....please.

[kcbooboo]

There are two different PAs for the VHF dash-mount radios: 25w and 50w. On both, the RF Output signal goes through a capacitor on its way to the antenna jack, so you should see an open circuit from the center terminal of that connector to ground. Since you're blowing fuses, I'd say something else is shorting out the A+ line, possibly the ground of the coax, or someone hooked DC to the radio incorrectly and the protection diode or a PA transistor shorted out. The power does come in via that heavy red wire. If you detach the PA from the radio chassis, you can disconnect the flat cable and find out if the short is on the PA board or somewhere else in the radio.

Bob M.

[Splat]

From when I removed the mini-uhf and its coax I might have a tiny piece of braid shorting the coax center pin and ground solder pads. I did check it with a magnifying lens to ensure it was clean. I'll check it out again. The radio was working fine until I had to putz with it. Thanks Bob.

[motorola_otaku]

I'm also leaning towards a short on the PA board from reverse-wiring the DC primary. I would try locating another PA (parts radios are cheap on Ebay) and swapping it out.

[Splat]

I'm also leaning towards a short on the PA board from reverse-wiring the DC primary. I would try locating another PA (parts radios are cheap on Ebay) and swapping it out.

Well, I asked my brother if he had the mains reversed and he emphatically stated he did not. Still, when I get home I'll dive back into it. Thanks.

[Splat]

I missed a few stragglers from the braid and they were shorting to the center conductor of the SO239. Hey, the eyes aren't what they used to be from reading too many damn resistors bands. Resoldered the antenna coax onto the board and SO239, powered her back up and all is well! Thanks for hanging in there with me, gents. Now, it's Miller time....well, Schaefer actually.