ept069611a single mosfet Galaxy DX 2547

[Hawkeye351]

Ok all,
Got another on my desk. It's a single final mosfet version Galaxy DX 2547 with the ept069611a board.

The issue is "no am transmit". Everything else works great. Sideband does around 42 watts on both LSB and USB. Just no AM transmit at all, no carrier or audio on AM. Nothing gets hot in the radio in AM except the pre driver gets pretty warm. No heating issues in SSB. This radio does not appear to be hacked up. The AMC is still intact at location Q39.

I've included some pics for those more advanced to look over.

Thinking the 2sb827 is shot, but I'll wait to hear from the pros.

 

[Handy Andy]

Then you said...​

Thinking the 2sb827 is shot, but I'll wait to hear from the pros.

Go get them Tiger...

You're earning your jacket...
(Or Fireproof Coveralls for your Soldering Station)
​

 

[Hawkeye351]

Yea, I noticed that spot. I looked more closely and I think I need to clean that area with alcohol. That looks like flux residue, but I was gonna go over that area.

Will the a1869 trans in front of the sb827 and one mounted on the chassis beside the audio IC work fine with a tip36c or should I replace those too (that is if they test fine) with an upgraded component?

 

[Hawkeye351]

Yep, gotta go over this mess. Seems like to hot of an iron or too long with the iron in that area, lol...

After cleaning:

 

[Handy Andy]

I just wanted you to avoid a downfall that happens with solder bridges - didn't want your winning streak to end with "magic smoke" wafting up thru the rafters...

That is the predriver there, and yes, you're right to be concerned about "warmth" - to the upper portion (towards that sidewall) is two parts one is a resistor the other is an RF Disc cap.

This predriver area can wreak havoc with "spurries" or worse a open ended harmonic or "squeal" that is the RF loop - not an audible one, make sure the resistor is still in value as banded - and the RF cap is not a dead short. What I mean by that is - you may have to test the cap out of circuit to make sure it is in value (as marked) so you don't ruin the rest of the strip getting hammered by extra frequencies out of the bandwidth that they are designed for,

It's why I mention "the value of X" - because on some schematics' Galaxy never put a part there - while in others - like one you have done previously - they used anywhere' from 5pF to even 1pF just to make a negative feedback path so it's open gain didn't fry the parts further down the chain. So those two parts are part of its gain control - with another that straddles the Collector To Base (as on another chassis you worked on) to offer a reduction in gain to remove unwanted artifacts and too overly zealous tuner's that Golden screwdriver the coils to make it appear to swing more - they only screwup the bandpass filter cans to upset the rest of the strip with a lot more RF out of band that what the rest of the strip should really be dealing with.

So now you know the rest of that story...

​

But in light of the changes, the TIP-36C should do just fine in there - but you will have to exercise some caution and know the age of the radio - for several Electrolytic caps can fail shorted causing the condition you describe so this too will be one of those chassis to have such a surgical effort made to it to keep it from failing again.

One main reason I ask - does the FM mode sound ok? But only gets you carrier on AM - or nothing at all?

No sound - we know - but do you get FULL CARRIER? Like, 8 Watts or so?

If you get Carrier on AM, can you AM Power control it on the main PCB?

If you can Then again, it's not that pass Transistor.

Then if FM works but no carrier on AM - then there is another problem with it we'll have to research further - that's is, if no carrier on AM but other modes work - it may be in its mode selector - even a bad diode can cause this so be ready...

 

[Handy Andy]

To help explain the "Solve For X" Locations - thanks for the photo of your Board...

​

The above is only if you encounter problems with the person / customer - or you, having issues with Low-drive amps or trying to limit a noise or power surge (chortle or other sonic - effect like clipping) like you want to allow for ALC - without the ALC clamping action being too severe - these areas help control the upper limit of gain in this section of the TX Strip - like low-level modulation - or FM - this area can benefit from a tweak or two to help.

This area is also bandwidth sensitive - so the Radio is 10-meter Yes but opened for 11-Meter - so this area can clean up transient and spurious issues that bring the wrath of the hams down on CB'ers. There is a cost - the 10-meter section still will work, but this lowers the 11-Meter power levels - which help a lot in low-drive amp interfacing and setting up drive levels.

It's only information, use it as you can to help or as you wish.

 

[NZ8N]

https://web.archive.org/web/2017060...cks.com/radios/galaxy/dx2547_mosfet/index.htm

Galaxy DX2547 is an FCC 40 CH AM/SSB radio, no FM. There are empty part places on the main board for where the FM parts would go.
The fact that the radio outputs 42 watts on a sideband mode tells me that the Power Regulator appears to be functioning properly, or might be hard clamped to 12v, isn't 42 watts from a single final a little high?

Test the "mirror board" (TP7/8/9 in the back) for about 12-13v DC in SSB, and about 5-6v DC in AM. Is there a dead carrier when you transmit in AM ??

 

[Hawkeye351]

Ok, sorry for delay. Had things going on.

Back to the radio issue.

NZ8N, there is no carrier whatsoever or modulation at all on AM. Sideband works great, swings to about 42 watts.

Here are the voltage results for the 2sb827:

Unkeyed
13.29 rear leg
0.76 center leg
13.72 front leg

Keyed
13.29 rear leg
0.03 center leg
13.72 front leg

Here is the voltage result from the tp7-tp9 strip:

Unkeyed
12.29 ssb
0.76 am

Keyed
12.29 ssb
0.03 am

 

[NZ8N]

The big transistor mounted to the side wall, the schematics call for that to be a 2SB754. The center leg should show 13v in SSB and 5-6v in AM.
And, this is what feeds the "mirror board" and TP7/8/9, for the Final and Driver. So, no voltage = no transmit power, even in SSB.

 

[NZ8N]

Both 2SB754 and 2SB827 are 7 amp rated max current, so in this circuit interchangeable. the 754 is 50v max voltage, the 827 is 60v. We are running them at around 13.8v, so same/similar for this circuit.
I suspect either this transistor Q54 or the "driver" transistor Q55 is bad. The Collector (center leg) should have voltage in all modes, not drop down to near Zero.

 

[Handy Andy]

Post #5 and Post #6 are for any radio from Galaxy (or any radio with multiple mode using AM Regulator) ...

So yes, a 2547 doesn't have FM, but uses a board CAPABLE of it. This was to help, if the radio has more than one mode - the AM Regulator is used in different ways between those modes. You can use the MODE switch to help isolate or localize the problem down even further to help with troubleshooting...I'm trying to make this a teaching moment...because the board uses jumpers to push signal from one section OVER the not-installed modes the board is CAPABLE of.

(*...SIGH...*) Getting busy with holiday so glad to see these threads still going...

Ok, some get into schematics, while others are completely lost, so I'm going to try and tie this together in a way that helps @Hawkeye351 find the answers...

There may be more than one reason why the Radio is acting this way.​

One of the bigger clues? Lot's of SSB power - so that may mean some work has been done to Q56.

Does RF Power work - at all?

Just remove Q56 and see if AM returns. If it does - you do not need to replace the AM Regulator.

Why? Well, it's why I asked about FM - if the Regulator was bad,

• blown shorted?
  • You'd have FULL AM no mod, Full SSB too
• Blown Open?
  • You'd have No SSB, No AM Carrier

So, you have...Full SSB mode, no AM POWER or Carrier - so therefore, if Q54 was bad - you'd have nothing or all of it...

If you had FM - would it still produce carrier?

Possibly - let me show you why...

IF the radios got mods in it,
What else was done - what parts do not belong in there?
Did those parts cause the Condition?
C235 is, for many to use as, a Direct-Injection point...
So, if it went bad, that FM Mode would allow Audio to pass,
because of where it's processed, it's further up the chain - at the PLL

HOWEVER:
IF the radios' C235 was shorted out,
Q58 could engage and all the AM POWER to adjust
AM or FM Carrier - would be sent thru Q58.
Potentially damaging the AM POWER Trimpot
and making it unable to provide FM Carrier - Killing both...
You Don't have this condition in your 2547,
you just have open holes for the parts that
can be put in there to do this...
This is just to help in diagnosing a problem.​

You have a few wrenches in the works - one being Q56...Q56 controls RF Power - so if it opened up or it's blown shorted - you'd have all kinds of SSB power - and no AM because it could be biased off.

Check C242 (And C238 if you have got a spare) - this thing is older than dirt - so the caps may have dried up and you already know what that means.

​

 

[Handy Andy]

PART II

I'll just leave this here...
​

 

[Hawkeye351]

Sorry guys,
Been busy doing the Christmas thang and haven't done anything else to it. Gonna wait til after Christmas so I can focus more on what I'm doing, lol....im sure you guys understand.

Once I get back on it then I'll pop in with an update. I am taking notes on what you all are stating. Thank you for hanging with me, you guys are great.

 

[Hawkeye351]

That is 2 diodes tied together. And there are 2 more like this in front of the audio IC. Just like that connex 3400 had, which I did not remove cause I was uninformed on what else was involved with it and what it was there for.

 

[Hawkeye351]