Avalon 737 Repair - 6922 Plate voltage...

[beatnik]

Now that you have the unit on the bench changing all the psu electrolytics is not a bad idea as they are inexpensive. Sometimes an esr meter can also help in spotting the capacitors that are developing resistance.
Use 105 deg rated parts with long life.
Also I would try removing the regulator and first of all make sure you get the unregulated dc voltage coming into the regulator.
Make sure there are no burnt or corroded pcb traces, you might have to remove the pcb to look on the bottom

 

[melmsmidth]

Thanks Beatnik.
Once I get the proper electrolytics I will check as you say, specially the unregulated voltage coming into the regulator. I have the suspicion that one of the caps I replaced might be the culprit so I will check it too, maybe I didn't solder it properly but it's just a guess, soldering it's the only thing I'm good at...
Since I needed to remove the board to replace the components I looked at the traces with care, there are a couple of them that looks a bit dark (the ones that comes from the transformer to the rectifier) but I have continuity. I reflowed the soldering on the molex connecting the trafo to the board too since one of the pads looked a bit burnt.
Do you recommend to solder a wire in parallel to be sure that I have a good connection? I can see clearly the traces so that could be easy.

 

[pucho812]

are the brown traces on the KBU6d?

 

[melmsmidth]

are the brown traces on the KBU6d?

Sorry, I’ve just seen your comment. Yes, the brown traces are the ones connecting the molex from the trafo to the two center lugs of the KBU6D (now KBU605).
One of the molex pins on the pcb were a bit burnt so I reflowed the solder there. Maybe I’m looking further than I need and it’s all about the traces?

 

[pucho812]

I hate to be that is common but there is a lot of current flowing there. Common to see brown traces over time from age. The bitch part is replacing the kbu6d. Most try and tackle it as one whole piece. This in turn damages it further because the heat from trying to desolder is absorbed by the kbu6d. Best to cut it out and tackle one pin at a time

 

[melmsmidth]

I hate to be that is common but there is a lot of current flowing there. Common to see brown traces over time from age. The bitch part is replacing the kbu6d. Most try and tackle it as one whole piece. This in turn damages it further because the heat from trying to desolder is absorbed by the kbu6d. Best to cut it out and tackle one pin at a time

Yes, I replaced it like that, cutting the legs first. Do you think the tracks can be damaged? Maybe it can't handle the same current anymore?
I will try to do some measurings and a couple of pictures, but have a busy day in the studio today, maybe tomorrow.

 

[melmsmidth]

Well, thanks a lot pucho812 and Beatnik. The problem was on the tracks indeed. I was searching far away what I had right in front of my nose, as a writer said once.

I soldered two cables in parallel with the tracks fron the trafo secondary to the rectifier and my 6,2 volts are back!

I just tested the unit for a little while because I used 50mm2 (20awg) solid wire that I had on hand.

So the question is: is it ok or I need something thicker due to the amount of current?

Just want to be sure that I don’t open the 737 again for a long while. And of course I want to keep my little studio smoke free!

 

[Jdm5149]

Well, thanks a lot pucho812 and Beatnik. The problem was on the tracks indeed. I was searching far away what I had right in front of my nose, as a writer said once.

I soldered two cables in parallel with the tracks fron the trafo secondary to the rectifier and my 6,2 volts are back!

I just tested the unit for a little while because I used 50mm2 (20awg) solid wire that I had on hand.

So the question is: is it ok or I need something thicker due to the amount of current?

Just want to be sure that I don’t open the 737 again for a long while. And of course I want to keep my little studio smoke free!

 

[Jdm5149]

Hi. Have a 737 with similar problem. Can u explain the track u repaired. I was in contact with a tech and he says to check the main board. But interested in ur repair. Thanks

 

[melmsmidth]

Hi. Have a 737 with similar problem. Can u explain the track u repaired. I was in contact with a tech and he says to check the main board. But interested in ur repair. Thanks

Hi, it was on the PSU board, one of the tracks coming from the molex to the diode bridge rectifiers, can't remember exactly wich one it was. In the pictures (not mine, taken from the internet) you can see the area where the rectifiers are located and the damage the heat can do to the molex connector coming from the trafo. Check the connections between the molex and the rectifiers, and the rectifiers and the rest of the circuit. I think the track was coming from the burnt connexions you see in the second picture.
But maybe first you need to check the voltages, to see if you have the 6,2V on the main board (that was my problem) but the rest of the voltages too.

 

[Jdm5149]

Hi, it was on the PSU board, one of the tracks coming from the molex to the diode bridge rectifiers, can't remember exactly wich one it was. In the pictures (not mine, taken from the internet) you can see the area where the rectifiers are located and the damage the heat can do to the molex connector coming from the trafo. Check the connections between the molex and the rectifiers, and the rectifiers and the rest of the circuit. I think the track was coming from the burnt connexions you see in the second picture.
But maybe first you need to check the voltages, to see if you have the 6,2V on the main board (that was my problem) but the rest of the voltages too.

Yes. I’m not getting the 6v for the heaters on main board or psu. Thanks for responding

 

[Jdm5149]

Hi, it was on the PSU board, one of the tracks coming from the molex to the diode bridge rectifiers, can't remember exactly wich one it was. In the pictures (not mine, taken from the internet) you can see the area where the rectifiers are located and the damage the heat can do to the molex connector coming from the trafo. Check the connections between the molex and the rectifiers, and the rectifiers and the rest of the circuit. I think the track was coming from the burnt connexions you see in the second picture.
But maybe first you need to check the voltages, to see if you have the 6,2V on the main board (that was my problem) but the rest of the voltages too.

Yes. Not getting the 6 v on the yellow wire