GP300 channel switch part ID

486dx4 · Post by **486dx4** » Wed Mar 07, 2007 10:29 pm

Hi - in the GP300 service manual I have the channel switch listed on the schematic as SW401T and it has a part number of 40-80502B01. I looked up the part to check availability on the internet (no MOL account here) and that number does not come up. I did see on a website for a GP350 a part number of 4080650D01 (SWITCH, ROTARY DIP 16 POS) which is available and is also listed as SW401T for that radio - the cost is around $19-22

The question is this the same part for the GP300? If not, what is the correct part number?

Thanks -

Al · Post by Al » Thu Mar 08, 2007 11:48 am

The original p/n you listed above is NLA, and the replacement is the same p/n you've listed above....4080650D01, list $27.25. The D01 is a 16 position switch.
Before you order a replacement, be sure to check the small SMT capacitors on the 1-2-4 and 8 outputs of the switch to ground for shorts...I've had some failures which would lead you to believe on casual inspection that the switch had failed, but always found that one of these caps had shorted.

486dx4 · Post by **486dx4** » Thu Mar 08, 2007 12:31 pm

Ok - I'll check those caps out. What is happening with the radio is that on position 13 (channel 13) the programmed channel on receive cuts out intermittently but this does not happen with the other channels. If you are on position 13 and you move the switch very slightly somewhat you can hear the radio cut out and in on the programmed channel and it does not happen all of the time. This led me to believe that that the switch is bad on that position 13 (bad physical contact or something). The other 15 positions seem to work fine with the same frequency info/tones/etc programmed when you very slightly move the switch in a similar manner.

I'll look at the schematic for those caps to try to answer this on my own but I guess if they short out no channels work at all?

Thanks so much for all of the good info.....

Al · Post by Al » Thu Mar 08, 2007 1:03 pm

Well, since the switch outputs are BCD, 1,2,4,8, if you had a shorted cap on the 1 line, all the odd channels would be problematic. Because you seem to have trouble with only ch 13, my guess would be that the switch is defective. If the 1 line is intermittently going inactive(high) due to a switch failure, then when it cuts out you should be able to hear whatever chan 12 is programmed for(8+4=12).

486dx4 · Post by **486dx4** » Thu Mar 08, 2007 1:49 pm

I just got home and looked at the schematic. It is BCD output like you said into U401 that tells it what channel to be on - interesting stuff. And depending on what caps shorted out which line you would see what was happening if you knew binary. So for line 2 shorting channels 1,2,5,6,9,10,11, and 12 would work only if I got the binary correct.

You do sometimes hear other channels on 13 when you move the switch so the switch sounds like the culprit with something going high telling U401 to tune into another channel.

Thanks again for the info....