M25C24 transistor replacement

[Flameout00]

I have an old GR1225 repeater setup which has intermittent tx problems with the r1225 radio (ABZ99FT4023) One day it will work fine putting out the 20+ watts on low power (I never operated it on high another does put out 40+ watts) and then there will be 0 watts output the next day, although with the ht in close proximity, it is putting out a tiny bit.

Would the most likely culprit be the M25C4 transistor? I watched a few videos and it looks to be a pain to replace, but I think I can do it. All I have to lose is the cost of the M25C4 but if there could possibly be another reason, maybe it is just scrap? I'd hate to toss it if it can possibly be repaired. One other question. Is the only difference between the 4023 and lower watt 4024 the rear part of the radio? (the heat sink part that actually contain the board with the M25C4)

 

[prcguy]

Did the TX power go away completely or does it come back? If it comes back its not the transistor. Possibly a relay if there is one or a cracked connection.

 

[WB5UOM]

Or maybe the solder on the base and more likely the collector needs to be reflowed?

 

[prcguy]

Or maybe the solder on the base and more likely the collector needs to be reflowed?

Probably not, the PA and driver transistor have large flat leads with lots of surface area, very unlikely there will ever be a bad connection on those. You might look at the chip caps in the circuit, they can crack under mechanical stress. I would fire the transmitter up and push down or tap on all the components in the PA chain when its in the failed mode. If it is an intermittent connection sometimes spraying freeze spray on individual components can find the problem.

You didn't mention if its completely dead or if the power comes and goes.

 

[Flameout00]

Thanks for the tips. It did it twice,, where it was working fine,, would stop and then work again. It still powers on fine, the red TX light illuminates when transmitting but showing 0.00 on the watt meter (I tried the same cable and watt meter on another radio and it was working fine, so can't be the cable or meter)
I'll try pressing down on some of the components to see if that helps. I also tried reflowing the solder, but it didn't help.
Can that rear portion, with the M25C24 and larger heat sink work with the lower power r1225? I thought that if it could, I could eliminate which part of the radio is actually bad. I would think that the 1-11 watt r1225 is completely different. I see that the FCC ID sticker is actually attached to the heat sink and not the radio, which made me think that might be possible

 

[WB5UOM]

I have not looked, but Is it really that much different than the gm300 pa's?
Ive resoldered so many of those thru the years I cant count.

 

[WB5UOM]

Now that I am where I can look at the picture, I would reflow the base and collector of the final. easy low stress test..if it helps fine, if not you wasted 5 minutes.
Looks just like a gm300 pa

 

[Flameout00]

Now that I am where I can look at the picture, I would reflow the base and collector of the final. easy low stress test..if it helps fine, if not you wasted 5 minutes.
Looks just like a gm300 pa

I gave it a shot, but didn't make a difference. Still no tx power. Do you think the pa board from the gm300 is the same and would work with the r1225? The gm300's are a lot easier to find than the r1225's are. That would be a nice easy swap if it would work!

 

[AM909]

How much 12V current does it draw, both "normally" and when failing?

 

[Flameout00]

How much 12V current does it draw, both "normally" and when failing?

Hmm, that I don't know. Guess I should have checked that before I removed the M25C24 from the board. I probably removed it a bit prematurely

 

[Flameout00]

Comparing the gm300 pa to the r1225 pa, there are some obvious differences although they are the same size and would fit, but probably not work (the one photo has a typo. Says gr300 instead of gm300)

 

[prcguy]

At this point it will be easier and cheaper to replace the entire radio.

 

[Flameout00]

At this point it will be easier and cheaper to replace the entire radio.

Yes, you're probably right, but they are so hard to find. I did order the replacement M25C24 so I'll at least give that a shot. Either it will work or I'll have yet another radio for the scrap pile

 

[prcguy]

Yes, you're probably right, but they are so hard to find. I did order the replacement M25C24 so I'll at least give that a shot. Either it will work or I'll have yet another radio for the scrap pile

Do you have access to a high frequency oscilloscope like 400-500MHz? If its in a broken state you can probe along the circuit and see where the RF stops or takes a big hit in level. Even a 200MHz scope should work for this.

 

[RFI-EMI-GUY]

I have an old GR1225 repeater setup which has intermittent tx problems with the r1225 radio (ABZ99FT4023) One day it will work fine putting out the 20+ watts on low power (I never operated it on high another does put out 40+ watts) and then there will be 0 watts output the next day, although with the ht in close proximity, it is putting out a tiny bit.

Would the most likely culprit be the M25C4 transistor? I watched a few videos and it looks to be a pain to replace, but I think I can do it. All I have to lose is the cost of the M25C4 but if there could possibly be another reason, maybe it is just scrap? I'd hate to toss it if it can possibly be repaired. One other question. Is the only difference between the 4023 and lower watt 4024 the rear part of the radio? (the heat sink part that actually contain the board with the M25C4)

That solder on the upper right (emitter) has a strange round volcano. Is there a via or something below that has cold solder?

 

[Flameout00]

That solder on the upper right (emitter) has a strange round volcano. Is there a via or something below that has cold solder?

I reflowed all of those questionable areas, just to be sure, but didn't help. As for the oscilloscope, I don't have one (I don't think I'd even know how to use it if I did) I don't know anyone local that has one either. I really don't know too many of the hams in my area. I always mean to get out to the hamfests and gatherings, but never seem to

 

[Flameout00]

Today I replaced that transistor and just as many have said, it wasn't the problem. Still showing no tx power, even though it is clearly transmitting but probably at a much reduced output. I'll give one more shot at reflowing some of the solder joints, but I think it's just another radio for the scrap pile as I own zero test equipment, other than a volt/ohm meter, so really can't do much in the way of testing components

 

[prcguy]

Today I replaced that transistor and just as many have said, it wasn't the problem. Still showing no tx power, even though it is clearly transmitting but probably at a much reduced output. I'll give one more shot at reflowing some of the solder joints, but I think it's just another radio for the scrap pile as I own zero test equipment, other than a volt/ohm meter, so really can't do much in the way of testing components

You can make an RF probe for your voltmeter using a 1N34 diode and a few other parts. That will allow you to probe the amplifier chain and see where the RF stops. Here is one example from N5ESE.

 

[Flameout00]

Just another question regarding the r1225. I picked up an old Radius M120 (was looking for the GM300) because the rear portion looks very similar to my bad r1225. The M120 was putting out about 38 watts when I tested it and the radio appears to be working just fine.
I took the rear finned part of the M120 and attached it to the r1225, (although there is one extra antenna wire - no big deal) I have to admit that I was surprised that my r1225 was now working as a repeater again!

The only problem is the output is much lower now on the r1225 than it was on the m120. I'm getting about 6 watts on low and about 14 watts on high. Would trying this with the slightly higher power output gm300 maybe work better? The Radius r1225's are hard to find and this $20 m120 was certainly easier, cheaper and quicker than the two transisistors I replaced (and it still didn't work)

W

 

[Flameout00]

Just another question regarding the r1225. I picked up an old Radius M120 (was looking for the GM300) because the rear portion looks very similar to my bad r1225. The M120 was putting out about 38 watts when I tested it and the radio appears to be working just fine.
I took the rear finned part of the M120 and attached it to the r1225, (although there is one extra antenna wire - no big deal) I have to admit that I was surprised that my r1225 was now working as a repeater again!

The only problem is the output is much lower now on the r1225 than it was on the m120. I'm getting about 6 watts on low and about 14 watts on high. Would trying this with the slightly higher power output gm300 maybe work better? The Radius r1225's are hard to find and this $20 m120 was certainly easier, cheaper and quicker than the two transisistors I replaced (and it still didn't work)

W

Actually, I think the m120 and gm300 might both use the same PA?? ABZ99FT4043 438-470 MHZ 48 watt and the r1225 is ABZ99FT4023 444-474 MHz 50 watt