So back on this radio. I notice I even have bias on the final when the radio is off. Like we talked about there is always power going to final. Am I still looking for a leaky receive transistor not shutting off?
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HR2510 about 15ma of final bias before mic is keyed.
- Thread starter Low_Boy
- Start date
The MRF 477 itself could have reverse leakage, seen it many times.
Lift one end of R158, the 82 ohm to the left of VR112. This will cut the bias voltage if there is any. If you still see the 15ma then you know the final has a leaky CE junction and needs to be replaced.
Lift one end of R158, the 82 ohm to the left of VR112. This will cut the bias voltage if there is any. If you still see the 15ma then you know the final has a leaky CE junction and needs to be replaced.
Well I have to say I was never so happy to have pulled one end or R158 and still have the same problem. The finals are so expensive for these radios. Now back to finding the faulty component. Thank You.
Hit another road block. Not being the best at schematics. Q136 good. Q127 good. With Q127 removed same problem so no need to check Q125 I guess. IC4 all good but pin4 is a bit high 4.1V should be 2.7V I do not see how that has anything to do with my problem. If I am tracing this right I see it has nothing to do with final power. Any suggestions are appreciated.
Going back to post #6...
Any recent work done to the RF amp RX side?
Why?
IF leakage...
If you had such a device, a simple Frequency counter made for wideband 10MHz on up - should be able to see as a birdie...
Any recent work done to the RF amp RX side?
Why?
IF leakage...
If you had such a device, a simple Frequency counter made for wideband 10MHz on up - should be able to see as a birdie...
This is a radio I bought a while back. No recent wok jumps out to me. I took the glue off all the toroids thinking the glue may have went through some of the coating and caused a short. But that was not a problem. I will have to keep looking. I did move some parts in switching transistors but no change.
Hmmm...
Ok, there's several reasons as to why I asked that.
One - rear panel heat sink - even the antenna connector being "plated" still will give you headaches - age and oxides are the problem here...
But, too - there is a section that many fiddle with, but then as they twiddle, they also find that it helps them with RX and TX improvement - it's the DO NOT ADJ stickers on the RX side that I ask, because once you fiddle with them, many retune and tweak these to improve the performance for 11 meter - but often forget about what else it can tune...
Don't worry, I'm guilty too...
Although not a big deal, the coils were really made for the 10 meter band - many retuned these to the lower 11 meter and just called it good. But there are caveats to the problem - I'll even admit I was not aware that these coils were not just for power but to reduce the spurious emissions of the Amateur band too.
They helped remove the lower and upper bandwidth products of the mixer. The thing uses a simple 7MHz clock at the CPU - so it starts it's day at that frequency - everything else is timed by it but left on the Main PCB - the CPU "sniff" but sits in the Mezzanine.
Since this is low-level modulated - they are specific to and designed for 10 meter - although you could use them on 11 meter and even 12 meter - but the caveats are the potential leakage of IF out of the strip into the radio and even out the antenna. It's very broad banded to begin with - the thing can even go as high in TX operation that can get you jailed for interfering with State Police bands in the 30~32 MHz range. At least they can throw that into the evidence cart along with the Spectrum profile if they decide to push an interference case. The stories you hear in the shop you learn from.
It's when it goes down the strip, does the IF and mixer leak problem rear it's ugly head - remember the carrier "sweep" effect and killed RX sensitivity with sometimes a Full Scale reading. I had (got) a long talk from one techs' of the last shop I worked for - that reminded me in front of others that the Radio is for Amateur bands only - don't "RETUNE" this for CB because they asked for it on the invoice - you know better.
He pointed out the C118 "NFB Fix" in a 2600 that Uniden provided, and was able to demonstrate the "leakage" effect I mentioned earlier. Again, two types of Filter elements one for TX and one for RX - from the retune of the FT104/FT101 - so you know, you can see it too - he used his GDO to neutralize my tune up right in front of me - so I know there is an IF issue - it's also why they say DONT ADJ - because of the problems you may have if you do. (It narrows/peaks it for Amateur, by adjusting these two Filter elements to open it up - you're offsetting the peaking to make it work on many other frequencies - not just Amateur above 28.000MHz)
So to say this and that about the radio in general can help you or hinder you, I've found that the tech that used that Grid Dip Oscillator as an RF sniffer - worked for a major brand - so in their eyes, they are responsible for what they produce and know it's limitations - if you make the choice then all of the results - positive or negative - fall on you
So not here to beat you up, I've been there already. As I help you or others as legacy and beyond - if they can use this information that's fine - I take no recourse - but I need to post this so my NDA with them is covered.
Ok, there's several reasons as to why I asked that.
One - rear panel heat sink - even the antenna connector being "plated" still will give you headaches - age and oxides are the problem here...
But, too - there is a section that many fiddle with, but then as they twiddle, they also find that it helps them with RX and TX improvement - it's the DO NOT ADJ stickers on the RX side that I ask, because once you fiddle with them, many retune and tweak these to improve the performance for 11 meter - but often forget about what else it can tune...
Don't worry, I'm guilty too...
They helped remove the lower and upper bandwidth products of the mixer. The thing uses a simple 7MHz clock at the CPU - so it starts it's day at that frequency - everything else is timed by it but left on the Main PCB - the CPU "sniff" but sits in the Mezzanine.
Since this is low-level modulated - they are specific to and designed for 10 meter - although you could use them on 11 meter and even 12 meter - but the caveats are the potential leakage of IF out of the strip into the radio and even out the antenna. It's very broad banded to begin with - the thing can even go as high in TX operation that can get you jailed for interfering with State Police bands in the 30~32 MHz range. At least they can throw that into the evidence cart along with the Spectrum profile if they decide to push an interference case. The stories you hear in the shop you learn from.
It's when it goes down the strip, does the IF and mixer leak problem rear it's ugly head - remember the carrier "sweep" effect and killed RX sensitivity with sometimes a Full Scale reading. I had (got) a long talk from one techs' of the last shop I worked for - that reminded me in front of others that the Radio is for Amateur bands only - don't "RETUNE" this for CB because they asked for it on the invoice - you know better.
He pointed out the C118 "NFB Fix" in a 2600 that Uniden provided, and was able to demonstrate the "leakage" effect I mentioned earlier. Again, two types of Filter elements one for TX and one for RX - from the retune of the FT104/FT101 - so you know, you can see it too - he used his GDO to neutralize my tune up right in front of me - so I know there is an IF issue - it's also why they say DONT ADJ - because of the problems you may have if you do. (It narrows/peaks it for Amateur, by adjusting these two Filter elements to open it up - you're offsetting the peaking to make it work on many other frequencies - not just Amateur above 28.000MHz)
So to say this and that about the radio in general can help you or hinder you, I've found that the tech that used that Grid Dip Oscillator as an RF sniffer - worked for a major brand - so in their eyes, they are responsible for what they produce and know it's limitations - if you make the choice then all of the results - positive or negative - fall on you
So not here to beat you up, I've been there already. As I help you or others as legacy and beyond - if they can use this information that's fine - I take no recourse - but I need to post this so my NDA with them is covered.
Humm. I have not adjusted anything yet. I will fiddle with those do not adjust coils and see what happens. I am not at the radio now but I do not remember if they look pampered with. I will mark thim first. I personally have adjusted many of the do not adjust with out problem. If that was the problem here it would be a easy fix.
Andy. I finished my one project and back on this. I would have to say that the, do not tune stickers on this radio may have never been touched. They are stuck on pretty good and seems like the factory glue. Do you think a problem in the front of the radio can be causing this? It appears someone changed a plug on the upper board. The wires all look like they go to the correct places. I really do not like taking the face plate off on these but I am now getting pretty good at it.
The mezzanine board can influence but if the 15mA is the ONLY problem, then a law of diminishing returns applies here.
Occam's Razor too, you pretty much done all the checks, we trust ya'
So to see this 15mA - it may be from a poor CE junction on the MRF477, or something even more exotic
You may be chasing after ghosts - There are many places that use IF - so it's not improbable that the leakage can simply be a routed cable wire unshielded - that the rest of the radio picks up and even then - it's still present no matter what you do to tame it.
You already know the radio is old, and much of the radio is stock - you know that radio better then the rest of us so we can only guide you.
Others things are caps - many RX caps and PIN diode sections do age, and nature is not their friend - electrical and static pokes and spikes do take their toll.
Wanted to point out something...it's in the parts list. - Came across this with lot's of radios - not just Uniden.
This is just some of the parts list for your radio.
Note the ratings, designation and in the Electrolytic ones, some have "C" rated markings.
Many of the above caps are SPECIFIC in NEED to maintain the performance of the circuit they are in.
Some need need to be NPO but others are literally Sand Grains sandwiches - two plates and dirt in between.
All this construction details and they use cheap capacitors. No, not really - but look, since when have we seen prices like that in a while?
These break down over time, they become less effective but are still useable - the are degrading as you use them. Any extra spikes, surges or even physical jots can shorten their lifespan even more.
Come-on' Andy, they are ceramics - yes, yet they too can age and puncture just like the rest of their Aluminum Can brothers. They are durable, and that radio is nearing 3 decades of notoriety and it still runs, can't say that about too many other things in life - except us.
So you either bite the bullet and rebuild all of them, of just live with the 15mA as a possible hit against the Emitter to Collector Junction and hope that MRF477's can come back in style every once and a while.
To me, you're right to ask about the 15mA condition, but what we've suggested and if followed - tested and proven using the suggestions we provided, does not to affect this draw, then you're covered, for we can only provide a guidance in using our collective Database of experiences.
It's not their Best side,
But it proves they too needed maintenance.
So in light (SIC) of the condition, and the tests you've performed using our directions, suggestions and Nomenclature - your concern is warranted, but we can't offer any more advice except to turn off the radio - decommission it from service and pack it away and hope for the day that the second coming of Uniden will arrive and you're radio will work flawlessly forevermore.
Occam's Razor too, you pretty much done all the checks, we trust ya'
So to see this 15mA - it may be from a poor CE junction on the MRF477, or something even more exotic
You may be chasing after ghosts - There are many places that use IF - so it's not improbable that the leakage can simply be a routed cable wire unshielded - that the rest of the radio picks up and even then - it's still present no matter what you do to tame it.
You already know the radio is old, and much of the radio is stock - you know that radio better then the rest of us so we can only guide you.
Others things are caps - many RX caps and PIN diode sections do age, and nature is not their friend - electrical and static pokes and spikes do take their toll.
Wanted to point out something...it's in the parts list. - Came across this with lot's of radios - not just Uniden.
This is just some of the parts list for your radio.
Note the ratings, designation and in the Electrolytic ones, some have "C" rated markings.
Many of the above caps are SPECIFIC in NEED to maintain the performance of the circuit they are in.
Some need need to be NPO but others are literally Sand Grains sandwiches - two plates and dirt in between.
All this construction details and they use cheap capacitors. No, not really - but look, since when have we seen prices like that in a while?
These break down over time, they become less effective but are still useable - the are degrading as you use them. Any extra spikes, surges or even physical jots can shorten their lifespan even more.
Come-on' Andy, they are ceramics - yes, yet they too can age and puncture just like the rest of their Aluminum Can brothers. They are durable, and that radio is nearing 3 decades of notoriety and it still runs, can't say that about too many other things in life - except us.
So you either bite the bullet and rebuild all of them, of just live with the 15mA as a possible hit against the Emitter to Collector Junction and hope that MRF477's can come back in style every once and a while.
To me, you're right to ask about the 15mA condition, but what we've suggested and if followed - tested and proven using the suggestions we provided, does not to affect this draw, then you're covered, for we can only provide a guidance in using our collective Database of experiences.
It's not their Best side,
But it proves they too needed maintenance.
It is a tough one. I changed a lot of caps in that back section. I may replace them all and hope one is shorted. Oh well something to ponder over LOL.
Update:::: even though this radio was putting out 30 watts I got sick of testing parts and everything checking good. I lastly tested the final and it turned out to be bad. If only finals were readily available. For a low price that is.
