What you are describing is typical when the audio PA is loaded badly or is self-oscillating, and drawing excessive current. You should be able to bypass the 12v to the audio PA on the regulator board as it only feeds the audio PA to the best of my recollection... It does indicate a problem if 2 IFAS boards do it, but in the bigger picture it is an unused circuit in a voter rx, so it may be easier to move on... If the caps are weak on the 12v, it could just be allowing the audio PA to be unstable as there is a feedback loop in the windings of the audio PA transformer and if power is unstable it could become an oscillation and be what you are seeing run off and blow the fuse....
The mod I described is on older IFAS boards and eventually became incorporated into new boards, swapping the component in the feedback winding of the transformer.. Off hand I think it was a cap to ground which was changed to a resistor to ground... and it stopped oscillation in the circuit... The LBI's are RB website, quick and dirty may be disable the 12v to the audio finals and it should draw a lot less current. It also seems to me one of the audio pa transistors was tab ( collector ) hot and maybe the hot tab mount insulators melted causing the 12 to short to ground of the heatsink... if you have a direct short, start there... but 2 IFAS boards doing same... is curious... ohming 12 v to ground on the IFAS side of the fuse would tell if you have a direct short or a current run-away or similar... Doug KD8B At 09:45 PM 12/11/2007, you wrote: >Hi Eric, > >I went back to the site today and pulled the receiver chasis. I'm >more of a "SpectraTac" person myself so bare with me. > >This receiver is a 19 inch rack mount voting MastrII receiver. The >only number stamped on the rear of the chasis is 19D41754GG7. It has >two optional boards installed, the CG decoder (dip switch version) >and the status tone (1950hz) generator board. > >The 10v regulator board has a model number of 320918G1 REV B. There >are two fuses on this board and I keep blowing fuse 801. (802 has >never blown yet) > >Interesting enough, I looked inside of another identical (looking) >receiver, and it's 10v regulator board only has one fuse on it. (but >that receiver is fine so I ain't messin with it!) If I had to guess, >I would say that the one fuse board is of older vintage than my 2 >fuse board based on appearance only. (it just looks older, caps, etc.) > >With the receiver now on the bench I'm feeding it with 13.8 volts >from my Astron VS12M. The ammeter goes up just over an amp and then >fuse 801 blows. I removed the IFAS board from the chasis and the >receiver now draws close to nothing, the 10v regulator measures >10.01, and no fuses blow. Put the IFAS board back in, fuse 801 blows >again. So....I put in another IFAS board, and again my fuse 801 >blows. Needless to say, I'm not sure what the problem is yet. > >I have no documentation so I can't help with LBI's. Not sure if I >should replace the two caps on the 10v board (200uf at 18v and 400uf >at 18v) because the 10 volts looks great when there is no IFAS board >installed. > >So....I ponder my next move.... > >Adam N2ACF > >At 20:37 12/11/2007, you wrote: > >Adam, > > > >I am struggling to understand which receiver you have, so that I can > >understand where the fuse is in the circuit. I am fairly new to the GE > >radio scene, so I hope you will indulge me a little. > > > >It will help me, and perhaps a few others, if you identify exactly what > >model or combination radio receiver you have, and which LBI you are > >referring to. As one who submits scanned LBIs to the GE Master Index, I > >really want to know about any LBIs that are lacking, so that I can locate a > >needed hard copy and fill that void. Thanks! > > > >73, Eric Lemmon WB6FLY > > > > > >-----Original Message----- > >From: > <mailto:Repeater-Builder%40yahoogroups.com>[email protected] > >[mailto:[EMAIL PROTECTED] On Behalf Of Adam C. Feuer > >Sent: Tuesday, December 11, 2007 3:49 AM > >To: > <mailto:repeater-builder%40yahoogroups.com>[email protected] > >Subject: [Repeater-Builder] GE MastrII Auxiliary Receiver > > > >Hello All, > > > >Yesterday, I had to go up the mountain to the repeater site because I > >noticed that my GE voting receiver was not working. When I got there, > >I found that one of the fuses had blown. I believe it was fuse 801 > >and it had a 1amp glass fuse in it. > > > >Not being fully equipped to trouble shoot ( I actually left work due > >to curiosity to see what was wrong) I simply replaced the fuse and > >the receiver came back to life working perfectly. I checked it > >periodically on my way back to work and home for the night and it was > >working fine. > > > >I come to wake up this morning and the receiver is dead > >again. Before I attempt to sneak out of work today, has anyone seen > >this fuse blow multiple times in this 19inch rack mount receiver? > >This particular receiver is being fed with an external 12volt source > >(not a supply attached to the receiver) that feeds other 12volt > >devices which are all working fine. I'm going to stop at the local > >two way shop and see if I can find a diagram but until then, I was > >wondering if anyone has had this trouble before. > > > >Thanks in advanced..... > > > >Adam N2ACF > > > > > > > > > > > > > > > > > > > > > > > >Yahoo! Groups Links > > > > > > > >
