Lafayette ssb 140 info needed low ssb power

[dj56]

Was using the radio this morning working fine then something happened now just about 2 watts on Am and about 6-8 watts on ssb both lower and upper.

Radio was doing 15 watts ssb the dropped to about half the out power.

Radio dead on frequency and receive is great
No burn marks on the bottom pc side.
I pulled both finals 2sc 1969 and 2sc2166 and both are ok.

Seem like rf out power just dropped in radio.

Any suggestions Im going to get out the service manual later tonight and study it and see if i can figure this out

Forgot to add there is very little modulated audio going out on AM its now backwards modulation and ssb will get a 5-8 watt carrier this is with a turner hand power mic.

Radio was doing about 15 watts SSB and about 5 watts AM now all low rf out.

As of today I just replaced the finals with HG 1969 and 2166 and same results low ssb power.

If i say ah ah into mic on ssb about 3 watts and if i whistle it will peak to maybe 7 watts max

thanks for any help

[Mitch]

There is a coil with a core right behind the output heatsink, is that burned? Take it out and re-wind with 4½ turns of enamelled copper wire if it shows any signs of stress. It was a common failure point.

[dj56]

There is a coil with a core right behind the output heatsink, is that burned? Take it out and re-wind with 4½ turns of enamelled copper wire if it shows any signs of stress. It was a common failure point.

I looked and nothing burnt as the coil will adjust power out and I put a meter on it and is not open

[UK-Ham86]

Check the AVR, Q44, 2SD325. Transistor in the left hand circle, mounted on heatsink.

Can be replaced with TIP41

Also check the Inductor, I think it's the one in the right hand circle but it's been a while so it may be one of the other ones in that area, white plastic, non adjustable thing, if you've turned up the power (it shouldn't be doing 15W) they go shorted turns and cause low power.

[dj56]

Check the AVR, Q44, 2SD325. Transistor in the left hand circle, mounted on heatsink.

Can be replaced with TIP41

Also check the Inductor, I think it's the one in the right hand circle but it's been a while so it may be one of the other ones in that area, white plastic, non adjustable thing, if you've turned up the power (it shouldn't be doing 15W) they go shorted turns and cause low power.

On the Inductor where can they be bought im here in the States Boston Ma.

I will check the regulator i think its fine

[UK-Ham86]

On the Inductor where can they be bought im here in the States Boston Ma.

I will check the regulator i think its fine

It's nothing too special, the values are printed on top (and I think I may have directed you to the wrong one, but there's another real close by.) so you should be able to get a suitable replacement from almost any parts distributor but it won't look the same.

I would test the part first.

[dj56]

On the Inductor where can they be bought im here in the States Boston Ma.

I will check the regulator i think its fine

It's nothing too special, the values are printed on top (and I think I may have directed you to the wrong one, but there's another real close by.) so you should be able to get a suitable replacement from almost any parts distributor but it won't look the same.

I would test the part first.

Crazy question

Even though its putting about 6-8 watts this coil or regulator could still be bad???????

[UK-Ham86]

It's possible but there are other possible causes, we can only guess based on experience.

You can test the part if you have one of those Chinese transistor testers or some other way to measure inductance.

[dj56]

here is an update on this ssb 140 telsat.
I have run the radio on the 12v plug and all seems good 5 watt AM swings to about 10 watts and ssb about 13 watts.

When run on AC I get about 4 watts Am very little swing and ssb about 6-8 watts max.

I checked the Ac power supply and its dropping about 2 volts during transmit. I checked the power regulator and dropping there also.
So next the AC out of the transformer and loosing about 2 volts about 21v Ac to 19v AC which makes the dc voltage drop about 2-3 volts also
I think the transformer is bad I replaced the 2 filter caps and still same problem and the regulator seems to be working properly.

I checked the 4 diodes and all good replaced the 2 electro caps got same results 2v drop, go back to dc v in and all is ok.

I dont think i will be able to find a new transformer so is there a small power supply i can install in the radio plenty of room if transformer is removed

pws 140.jpg

3Screenshot_1.jpg

[Buick Mackane]

https://www.ebay.co.uk/itm/389339300647 ... A3RMPQEP8F

[dj56]

thanks im in USA and dont think that would fit inside the radio no demensions posted.

Also he does not ship to USA

thanks

[Mitch]

You won't need 30 amps, 5 amps will be plenty, I'm sure you could find something locally, or there's https://www.ebay.com/itm/186018427884 (and turn up the voltage).

[NM1020]

I'm not convinced it's the mains transformer. The secondary output of the transformer will droop a bit under load, but ultimately the regulator should be able to take care of that, 19 volts should still be enough head room for it to cope comfortably. Transformers can get shorted turns or go open circuit. If it had even a single shorted turn it would literally fry and you'd have smoke, heat and eventually a blown mains fuse, and this isn't happening. My money would be on a failing regulator and nothing else, unless there's a seriously high resistance bad connection somewhere that you've missed.

[dj56]

I'm not convinced it's the mains transformer. The secondary output of the transformer will droop a bit under load, but ultimately the regulator should be able to take care of that, 19 volts should still be enough head room for it to cope comfortably. Transformers can get shorted turns or go open circuit. If it had even a single shorted turn it would literally fry and you'd have smoke, heat and eventually a blown mains fuse, and this isn't happening. My money would be on a failing regulator and nothing else, unless there's a seriously high resistance bad connection somewhere that you've missed.

I did replace the Regulator 2sd525 and had the same results replaced C1 C2 and same results

[Stronty]

The guys over at Microchipz do a PSU board that may be more in keeping. If you are convinced it is the PSU.

They also did a fitting vid > Here

PSU for Jumbo.jpg

***EDIT*** You're in the USA, maybe not