Amp issue?

[Handy Andy]

If the meter lite is dim...

SIGH

Which 25 ohm "sand" resistor gets hot the quickest?

Then that "pair - one (or two) is blown shorted - sucks all current to ground...

Pipes don't always fail but you never know...wiring - long shot...Relay will go toast if left in this condition...as well as the other pills...

Base-Collector side - Base-Emitter side - check both sides of each in the pair...

 

[357magnum]

Hi Andy ! Welcome back ! 73 & God Bless , Leo

 

[Handy Andy]

Hey! Good to see you still around!

 

[Handy Andy]

Hopefully you're not in over your head yet...

when I had turned the amp on and turned my power all the way down on my radio the SWR at the radio used to go to 2.0 to 2.8 and when I turn the power to where I usually put it which I believe is about 6 Watts it goes back to normal(1.0).

See attached... I hope it can help...

400DX and 500DX are similar...

And I'll mirror, emphasize, 2nd the notion of, what Audio Shockwave and Nomad tells of...if your boards got bounced or somehow flexed - they can loosen parts - it can be something as simple as a cracked solder joint on up to a failed blown part BECAUSE the board bounced and shorted out a solder pad while keyed up or even sitting idle while driving.

You're also getting the CW version of what you get when you buy it new...Why?

Because of any mod's were done, you may have to undo them to get to the part(s) that need repair - it helps on wiring too - in case something doesn't seem right you can engineer a fix knowing before and after - all the works done to it...

 

[530]

Hopefully you're not in over your head yet...


See attached... I hope it can help...

400DX and 500DX are similar...

And I'll mirror, emphasize, 2nd the notion of, what Audio Shockwave and Nomad tells of...if your boards got bounced or somehow flexed - they can loosen parts - it can be something as simple as a cracked solder joint on up to a failed blown part BECAUSE the board bounced and shorted out a solder pad while keyed up or even sitting idle while driving.

You're also getting the CW version of what you get when you buy it new...Why?

Because of any mod's were done, you may have to undo them to get to the part(s) that need repair - it helps on wiring too - in case something doesn't seem right you can engineer a fix knowing before and after - all the works done to it...

Thank you. Not that experienced. Going to be sending it in lol.

 

[530]

Here's a pic of the inside, not much help for me. Everything looks and feels tight. Not going to mess with it and make things worse. Going to send it in. I have Gatekeeper but it seems people having trouble lately getting a hold of him. I have been given a name here in a message as well. I do hate shipping my equipment, so if anyone is reading this or if anyone knows someone who is in or very close to NJ, feel free to message me.
Thank you for everyones help.

 

[AudioShockwav]

I am on my phone and it is hard for me to tell, but look on the back board, is that a toasted 10 ohm on the back 2879 or just some kind of reflection?
If that resistor is toasted it is a good bet the transistor is as well.
Look at the other 3 for any signs of heat damage.
Is there any discoloration on the wires on the output combiner?
You saying it " clicks" when turned on makes me think it is pulling the relay into TX as soon as you power it up.

73
Jeff

 

[Handy Andy]

Found a couple of things...

The cap resistor combos used on the amp - the blue large body resistors - the color code of 20 ohm (Red - Black - Black), but schematically they use 39 ohm (Orange - White - Black)...

So already some works been done to it, but the resistors are not the issue, the caps in line with them are...

They look like AXIAL types, not radial. So to see that kind of work scares me - they are located as part of a feedback loop to keep the amp clean - there is a lot of power that pumps into this circuit (all four of those pills use this pairing) - and if the caps or resistors are not up to par or can't handle the rated power - they'll blow and well - as you can see by the RED ARROW - you have a blown resistor as Audio Shockwave has revealed.

So my research concurs with his - yes the repair is a bit or work to be done to get it back right...

 

[Ranch55]

Yes, same things I saw.
Feedback resistors and capacitors incorrect, at least one 10 ohm resistor blown which means the transistor is also. Maybe both.
Those Toshiba 2SC2879 transistors are very, very expensive now.
But, the amplifier can be repaired rather easily, just cost a few $$ .....
I have repaired a bunch of Texas Star amps over the years, and quite a few after someone else "thought" they had it fixed.......

 

[AudioShockwav]

Non red dot Toshiba 2sc2879 transistors are priced like gold.

73
Jeff

 

[530]

Non red dot Toshiba 2sc2879 transistors are priced like gold.

73
Jeff

Yes, same things I saw.
Feedback resistors and capacitors incorrect, at least one 10 ohm resistor blown which means the transistor is also. Maybe both.
Those Toshiba 2SC2879 transistors are very, very expensive now.
But, the amplifier can be repaired rather easily, just cost a few $$ .....
I have repaired a bunch of Texas Star amps over the years, and quite a few after someone else "thought" they had it fixed.......

Found a couple of things...

The cap resistor combos used on the amp - the blue large body resistors - the color code of 20 ohm (Red - Black - Black), but schematically they use 39 ohm (Orange - White - Black)...

So already some works been done to it, but the resistors are not the issue, the caps in line with them are...

View attachment 30959

They look like AXIAL types, not radial. So to see that kind of work scares me - they are located as part of a feedback loop to keep the amp clean - there is a lot of power that pumps into this circuit (all four of those pills use this pairing) - and if the caps or resistors are not up to par or can't handle the rated power - they'll blow and well - as you can see by the RED ARROW - you have a blown resistor as Audio Shockwave has revealed.

So my research concurs with his - yes the repair is a bit or work to be done to get it back right...

Ok thank you. Don't know how I did not see that. This thing has been working since the last time it was worked on in 2015 and was working before that and until now. If you see in the video it was worked on before and not sure who did what and in the video was also said to be a 400 that he changed to a 500 which my friend who owned said he didn't charge him for that and only paid for the wire upgrade and he had him make it so the power didn't switch down power when SSB Delay was on.
When you say $$$ roughly how much am I looking at from what you see?

 

[Ranch55]

At least two of these, plus about maybe $20.00 or so in misc. parts, plus any labor......

2SC2879A Transistor "Red Dot" Pb Free, RoHS compliant, Toshiba (Not for Export)

$104.95 ..... at today's current price, can change

2SC2879A Transistor "Red Dot" Pb Free, RoHS Compliant, MFR: Toshiba, No longer available for Export, (NOS)

 

[9C1Driver]

Holy crap they are expensive.

https://www.rfparts.com/2sc2879.html

 

[Handy Andy]

The kind of repair the tech needs to do to that amp - is the assembly details and in the LABOR.

Parts? Well, that varies, but per everyone else's and your own response - that is the cheap part.

The problem lies in the details of the rear board - with the burnt resistors. You have a lot of unsoldering and disassembly that is not for the feint of heart.

If it was just the pills, you can do that yourself - it only takes a hex wrench to unbolt and desoldering of the old part off ... the trouble is in the details of the work you HAVE TO REMOVE to pull away the wiring, cables and parts.

Once that's done, you have to clean up and take out any potential soldering bridges, blobs of solder, reposition parts that shift when the soldering is done and still molten - again the details.

Not to add more salt to the wound, the photo you send us also shows work performed and parts and the values in the positions are different. What I posted for you with the 400 and 500 DX models are Outcomms own selected values for their amps to be considered safe and provide the best Mean Time Between Failures or MTBF. They are chosen - not for performance and keying power - but for best overall performance to power ratio. To use such low value resistors in the main feedback loop (20 or if that is Brown - not Red - it's 10!) and alter the cap values - to survive from 2015 until now is a feat in itself.

I did a little more work for your photo - to show the relative parts you'll need to look at....and how they are placed in the schematic and on the board - so you don't panic over the bill they'll charge...

Remember what Audio Shockwave said earlier - parts on the board that have solder pads on top and bottom. Those pads hold that part and make the electrical connection - but if pads that touch the heat sink that are not supposed to (the air gap) - it will wreak havoc on the board. So parts that are repositioned or replaced, also have to be rechecked for depth so they not only meet the traces on the top of the board, but also to those UNDERNEATH the board that the parts "branches" from, so they don't touch the heat sink. Again details and assembly.

I've got an amp over here I ate my shirt on due to the user deciding to try and convert the amp from the CW version to the amp version without guidance. I use it not only as an assembly reminder to refresh my memory, but also as a "living lesson" in trusting someone else's knowledge of what they are supposed to do. They only did one mistake - else the amp itself is still pristine and I can use it as a template to help others...

The above is not to scare you - but to serve as a reminder. When things go wrong - they can go wrong in an unexpectedly big way.

Now you can understand why MOSFET amps are so popular, they are the cheap and easy way out of an expensive repair bill. It's expensive because of the type of necessary repair and the LABOR involved in it.

 

[530]

The kind of repair the tech needs to do to that amp - is the assembly details and in the LABOR.

Parts? Well, that varies, but per everyone else's and your own response - that is the cheap part.

The problem lies in the details of the rear board - with the burnt resistors. You have a lot of unsoldering and disassembly that is not for the feint of heart.

If it was just the pills, you can do that yourself - it only takes a hex wrench to unbolt and desoldering of the old part off ... the trouble is in the details of the work you HAVE TO REMOVE to pull away the wiring, cables and parts.

Once that's done, you have to clean up and take out any potential soldering bridges, blobs of solder, reposition parts that shift when the soldering is done and still molten - again the details.

Not to add more salt to the wound, the photo you send us also shows work performed and parts and the values in the positions are different. What I posted for you with the 400 and 500 DX models are Outcomms own selected values for their amps to be considered safe and provide the best Mean Time Between Failures or MTBF. They are chosen - not for performance and keying power - but for best overall performance to power ratio. To use such low value resistors in the main feedback loop (20 or if that is Brown - not Red - it's 10!) and alter the cap values - to survive from 2015 until now is a feat in itself.

I did a little more work for your photo - to show the relative parts you'll need to look at....and how they are placed in the schematic and on the board - so you don't panic over the bill they'll charge...

View attachment 30964

Remember what Audio Shockwave said earlier - parts on the board that have solder pads on top and bottom. Those pads hold that part and make the electrical connection - but if pads that touch the heat sink that are not supposed to (the air gap) - it will wreak havoc on the board. So parts that are repositioned or replaced, also have to be rechecked for depth so they not only meet the traces on the top of the board, but also to those UNDERNEATH the board that the parts "branches" from, so they don't touch the heat sink. Again details and assembly.

I've got an amp over here I ate my shirt on due to the user deciding to try and convert the amp from the CW version to the amp version without guidance. I use it not only as an assembly reminder to refresh my memory, but also as a "living lesson" in trusting someone else's knowledge of what they are supposed to do. They only did one mistake - else the amp itself is still pristine and I can use it as a template to help others...

The above is not to scare you - but to serve as a reminder. When things go wrong - they can go wrong in an unexpectedly big way.

Now you can understand why MOSFET amps are so popular, they are the cheap and easy way out of an expensive repair bill. It's expensive because of the type of necessary repair and the LABOR involved in it.

Thank you for being so thorough
Yes once i read the replies i knew it wasnt going to be cheap. Looks like ill be looking for a new one. Been thinking about upgrading anyways. Going to go for a 2x8 or straight 8.