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HR2510 low output

D

duldog

Member
Sep 26, 2011
19
0
11
hi everyone!

had recently acquired a "working" HR2510 with the MRF 477 finals

first time i switched on the unit, i notice that there is a "carrier" on ssb, and SWR goes haywire when the covered is off, max power is 40+ watts

reading the posts in this forum, i placed an insulator between the final transistor and the heatsink and that solved the "high" swr problem

i then noticed that the output went down to less than 20W, again reading through the posts i removed the two caps in parallel on the foil side of the board near to the final transistor and that solved the low output problem, its now about 30W out

later, while on transmit every time it becomes hot the fuse blows. i found out that the final transistor becomes very hot quickly and the the current goes up and then the fuse opens. the transistor even goes hot even without modulation

i checked the final/driver bias, the final bias was set to more than 150mA and same reading with the driver. I readjusted the bias so that its about 50mA as recommended in the service manual and the driver bias was set to about 60mA since it cant go lower

checked the output and its now about 15w max on ssb and 12w max on am, i adjusted both ssb and am power trimmers but it cant go past 15W but the finals don't heat up as quickly as before

can pls help me out what will i check next? thanks!
 

Sounds like it's time to box her up and send her off to Rogerbird or Doc. They are the top two Lincoln/2510 gurus.
 
You never want to place an insulator behind a MRF477 final! This transistor has its metal tab tied to the emitter terminal and it's supposed to be grounded through the lowest inductance path possible. That means through the mounting screw.
 
Shockwave said:
You never want to place an insulator behind a MRF477 final! This transistor has its metal tab tied to the emitter terminal and it's supposed to be grounded through the lowest inductance path possible. That means through the mounting screw.
Click to expand...

Nuff said. Hope ya didn't smoke your 70 dollar final.
 
Shockwav, numerous problems have been associated with the tab on the 477 mounted to the heatsink without an insulator and an insulating washer on the screw.
I have repaired a couple dozen 2510`s, 2600`s and a several lincolns that were so unstable they went totally wacky without it.
In each case, slipping an insulator, plastic washer and proper heatsink compound behind the final solved the problem with no loss of power, and no Ill effects to the radio.
My ChipSwitched 2510 has been running over 20 years with an insulator behind the final.
It is a well documented fault, and has surfaced many many times.


73
Jeff
 
AudioShockwav
hi! i've read most of your recommendations re: insulator on the finals of the hr2510 and its exactly what i followed and that really solved the "weird" swr problem

the main problem of my unit is that the previous owner may have adjusted the power output by using the bias pots

i replaced the driver bias diode so that it now reads 50mA while the finals bias is at 50mA also, the output is now 18w max (ssb)

i noticed that if i set the driver bias to about 80mA or more the output is going to about 20w max but i am afraid that this setting might burn the driver transistor

btw the unit has been previously modded with this
HR2600 Better Hi-Power
but they did not change the finals to MRF497

could this be the cause of low output? i will be doing some voltage checks compared to voltage chart on the service manual, will post back what will i find

thanks and 73!
 
Check the output with a different meter. I have one Rogerbird tuned and it reads low one one of my meters. I tried a different meter and it read higher. My other 2510 reads the same on both meters but for some reason this one reads different. Same with a HTX 100 Roger tuned for me. I have no idea what causes that but I sent the 2510 back to Roger and he double checked everything and could not find an issue. My Radio shack meter seems pretty accurate but the 2510 and htx 100 read low on it.
 
AudioShockwav said:
Shockwav, numerous problems have been associated with the tab on the 477 mounted to the heatsink without an insulator and an insulating washer on the screw.
I have repaired a couple dozen 2510`s, 2600`s and a several lincolns that were so unstable they went totally wacky without it.
In each case, slipping an insulator, plastic washer and proper heatsink compound behind the final solved the problem with no loss of power, and no Ill effects to the radio.
My ChipSwitched 2510 has been running over 20 years with an insulator behind the final.
It is a well documented fault, and has surfaced many many times.


73
Jeff
Click to expand...

This makes me fairly confident we have another problem that adding the insulator is covering up. You have to think about what insulating the emitter terminal does to the circuit. It causes more RF to be dropped across RE prime, thus lowering the gain of the stage. That could cause an unstable circuit to stop oscillating due to the drop in gain but it can also cause more problems by not allowing the transistor to see a low inductance path to ground.

Rather than looking to remove the low inductance path to ground we should be looking at the circuit to determine why it fails to run stable when the transistor is mounted as the data sheet recommends. I think we would quickly find other problems like lack of shielding between stages, poor decoupling from the DC feed, or missing negative feedback. Just because ungrounding the transistor tab restores normal function does not mean it was the best solution to the problem.
 
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Rather than looking to remove the low inductance path to ground we should be looking at the circuit to determine why it fails to run stable when the transistor is mounted as the data sheet recommends. I think we would quickly find other problems like lack of shielding between stages, poor decoupling from the DC feed, or missing negative feedback. Just because ungrounding the transistor tab restores normal function does not mean it was the best solution to the problem.
Click to expand...

I can agree that what you have posted may very well be correct Don, but without diving even further into the radio and trying to do other modifications, this simple fix allows the radio to function properly with no loss of power or any Ill effects to the transistor.
I am not the one who came up with the fix, a guy that went by Yaesu Tom first came up with it many years ago, and It has worked very well for me and many others.
If there is a better solution, I am all ears as these Transistors are now very expensive, and hard to find due to the many Chinese fakes being sold.
I am never opposed to learning something new.
73
Jeff
 
just an update

all voltages in the tx section are all on the mark as compared to the voltage chart in the service manual

also removed c132 and replaced driver bias diode as advised by rogerbird

still the radio output power is 15-18w max

rechecked all resistors in the tx section none seems to be open or changed value
checked all transistors (predrive-to-final) all of them passed ohmmeter test
its just my hunch that maybe one of them (before the final transistor) has lost some gain although they look ok on the ohmmeter, i don't know, too bad spares are not handy over here

running out of ideas:cry:

i really need help, thanks!
 
Last edited:
You have gone through most of what you can with the limited test equipment you have.
Replacement of final/or send it to Rogerbird.
RF Parts still has Genuine MRF 477 transistors, last time I checked they were about 48.00
You can also replace it with a MRF 455MA ( made by Maycom, good transistor) for $10 bucks less, but there is a little work involved, Rogerbird can Advise you about that.
Another resource is the HR2510 Facebook Page.
They are a group of guy that use/work on the rigs and some of them have been using the SD1446 and even a 2sc2290 in the radios as replacements, you might contact some of them there.
www.facebook.com/hr2510

Good Luck.

73
Jeff
 

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