Marshall VBA 400 Bass Amp / No Power

[sluckey]

I touched the small toridal transformer and it burnt me. It and the surrounding wires to and from it were so hot i could not even touch them for a second. I am surprised it is not on fire..

That's like a big clue. Worth mentioning at the beginning of the thread.

[plexi50]

Well i had the chassis on it's side and the transformers were at the top of the chassis. I was sitting and checking the board itself. It wasnt until this afternoon that i stood up and felt heat hit my forehead as i leaned over the top of the chassis. Thats when i touched the transformer and chassis.  Why didnt the mains fuse blow? Why didnt my lamp dimmer draw down?

[sluckey]

Threw in washer. Results

W22 & W19 = 94 VAC
W18 & W20 = 0 VAC
W12 = 3.20VAC
W13 = O VAC
TR2 is good

You should have 120VAC BETWEEN W22 and W19. If not, check links 7 and 10.
You should have 120VAC BETWEEN W18 and W20. If not, check link 11.
You should have 6.3VAC BETWEEN W12 and W13 only if primary voltages are OK and transformer is good.

Your cold transformer probably does not have 120VAC applied to the primary windings due to interlock relay or STBY switch or improper links. It may be normal for the other transformer to be hot. There's a lot of heater current flowing.

The 65760 transformer is for the heaters and other low voltages.
The 65765 transformer is for high voltages.

I would not call the transformers bad until you have measured 120VAC across the primaries.

[plexi50]

These are the voltages take between (across) each lead. Not from ground
The transformer was hotter than a power tube biased very hot. The chassis as well. Ive never seen a chassis get that hot. I do thank you for all your info and help. 


W22 & W19 = 94 VAC
W18 & W20 = 0 VAC
W12 = 3.20VAC
W13 = O VAC
TR2 is good

[sluckey]

These are the voltages take between (across) each lead. Not from ground
The transformer was hotter than a power tube biased very hot. The chassis as well. Ive never seen a chassis get that hot. I do thank you for all your info and help. 


W22 & W19 = 94 VAC
W18 & W20 = 0 VAC
W12 = 3.20VAC
W13 = O VAC
TR2 is good

You say TR2 is good. I ask, "What are you calling TR2?"

Your two readings for W12 and W13 'indicate' you are measuring in respect to something else. If you measure between W12 and W13 you only get one reading. BTW, W13 is connected to ground.

W22 & W19 = 94 VAC... This should be 120VAC coming from the power cord.  However, W22 must pass thru IR2. I'm guessing that IR2 may be a thermistor that is higher resistance when cold and lower resistance when hot. This would prevent high inrush of current at initial turn on, kinda like a 'soft start'. IR2 may explain why there is only 94 VAC between W22 and W19. IR2 may need to be replaced. For testing purposes, you can put a jumper across IR2.

W18 & W20 = 0 VAC... This should also be 120VAC coming from the power cord. Since you have 94VAC across W22 and W19, you should also have 94VAC across W18 and W20. Unless LINK 11 is not properly connected or you have a broken wire. It should be really easy to find out why you have zero volts across W18 and W20.

I would pull F1 and F2 fuses while troubleshooting the filament circuit. Just measure the unloaded filament voltage across W12 and W13.

At this point you just need to get 120VAC from the power cord all the way to W18 and W20. If you do that, the filament voltage may come up to 6.3VAC.

I'd like to see a hi rez pic showing the line voltage selection LINKs(1 thru 12) for the two transformers.

[plexi50]

You say TR2 is good. I ask, "What are you calling TR2?"

TR1 & TR2 are thermistors that limit the in rushing current. Both TR1 & TR2 read 2 ohms and have good continuity across them with no wires on the board.

Thats what i was checking yeterday with heater filament voltage being only on W12 only. And i expected to see 100VAC + on W18 & W20 which would have in turn shown filament voltage on W13. Link 11 and all other links on the board show continuity as to there layout (traces) with no wires attached.

Let me put the transformer back on the chassis and wire it up and i will check the voltages again on W18 & W20. I tell ya all these spade connectors on the board all have to be re-soldered. There all pretty wiggly. Let be pull the back board off the chassis and see what the solder connections under the board look like. My continuity checking may be showing good only becuse i am putting preasure on each terminal as i test them

[plexi50]

Ok i pulled the board from the chassis and found a trace @ W13 & W16 smoked at W16 solder trace. Trace broken and cracked. No continuity. Going over more of the boards pics now to see if there are any other funny looking joints. I will get back to the mains power transformer after i get this boards issues sorted out.

[plexi50]

Back Circuit Board pic's. I dont see any other solder cracks or broke traces. Going to re-solder them all good/

[sluckey]

TR1 & TR2 are thermistors that limit the in rushing current. Both TR1 & TR2 read 2 ohms and have good continuity across them with no wires on the board.

There is no TR1 or TR2 on the schematic provided. However, there is an IR1 and IR2. Is that what you are calling TR1 and TR2? If not, please show me a TR1 and TR2 on the schematic.

[sluckey]

Ok i pulled the board from the chassis and found a trace @ W13 & W16 smoked at W16 solder trace. Trace broken and cracked. No continuity.

Both of those connectors are for the HT transformer. They have nothing to do with the LT/Filament transformer. Put your shotgun down and put your thinking cap on and do some logical troubleshooting.

I'm trying to get you to divide and conquer. Fix the filament circuit first. First, you should be able to take that cleaned up drawing I posted and find out why there's zero volts across W18 and W20. Second, you should also be able to find out why there is only 94VAC across W22 and W19. I can't see it taking more than about 5 minutes to clear those two issues. When you clear these two issues, you should have 6.3VAC filament voltage between W12 and W13, unless the LT transformer is bad.

[SILVERGUN]

I'm trying to get you to divide and conquer.

This is how I work my way through the most difficult schematics.....beak the print down into smaller, more digestable pieces......I just didn't know how to explain it as well as sluckey has 

Now that he has joined us, I have obviously bowed out (hopefully, gracefully)....
There's no reason for me to add to your confusion ........he's got it handled better than I could ever hope to, and I will follow along and learn what I can....

His methods are rock solid and if you continue giving him answers, I have all the confidence in the world that you WILL fix that thing

[sluckey]

Hey, stick around. I'm just trying to point plexi in a particular direction. Once he locks on I'm likely to sit back and let him run.

[plexi50]

Yes im sorry. I have been calling IR1 & IR2  / TR1 & TR2. Im thinking thermistors and they have stuck in my head as TR1 / TR2. I will rewire the mains transformer tommorrow after i finish re-soldering and putting the board back in place. Can i just test the power transformer itself on the bench right now or would it be better for it to be in place on the board?

[SILVERGUN]

Hey, stick around. I'm just trying to point plexi in a particular direction. Once he locks on I'm likely to sit back and let him run.

Thanks for the "vote of confidence" sir (I'll take the liberty of taking it that way ).....
if you tell me to stick around, I'll do it................

That schematic was starting to get to me too, and I never wanted to pretend that I could definitely fix it from here...

I learned the value of a great picture tutorial when you came aboard (reply #44), and I will remember to use that technique in the future....
It looks just like the Miller/Lincoln troubleshooting I'm used to.

What's the deal with W14 and W17 appearing on the primary and secondary connections? (don't know if I've seen that before)

[plexi50]

Board back in chassis. Wiring mains PT up now. No i love it when Steve makes me think. Back in a bit/

[sluckey]

I will rewire the mains transformer tommorrow

There is no "mains" transformer. There is a HT transformer for B+. And there is a LT transformer for filaments and low voltages. The transformer that is drawn directly to the right of the mains switch is the LT transformer.

Here's how the power switches function... The mains switch applies line voltage directly to the LT primary which should bring up filaments immediately. The mains switch also sends line voltage up toward the HT primary to develop B+ voltages. But the line voltage has to pass thru interlock relay contact RL1b and then thru the standby switch before reaching the HT transformer. IOW, RL1b contacts must be closed and the standby switch must be closed before line voltage is applied to the HT primary. So, when you throw the standby switch you are actually sending line voltage to the HT transformer.

Can i just test the power transformer itself on the bench right now

Absolutely. In fact, since you have it disconnect, I highly recommend doing so. Here's what you need to do...

I'm assuming you are talking about the 65760 LT transformer. If you still don't know which transformer is which, now is a good time to learn, before testing the transformer. Refer to my simplified drawing as needed. Jumper W22 and W18 together and connect the black wire of a power cord to W22. Jumper W19 and W20 together and connect the white wire of that power cord to W19. Don't worry about the green wire in the power cord. Now turn your variac off and set the dial to zero and plug that power cord into the variac. Set your meter to read AC volts and connect the probes to W12 and W13 (6.3VAC secondary). Now turn your variac on and turn the dial up a little bit so that you have 12VAC out of the variac. The voltage on your meter should be approx. 0.63VAC. If no smoke, turn the variac dial up so that you have 120VAC out of the variac. Your meter should now read approx. 6.3VAC.

If you understand and follow the above procedure EXACTLY but don't have 6.3VAC on your meter the LT transformer is bad.

[sluckey]

What's the deal with W14 and W17 appearing on the primary and secondary connections?

The W14 and W17 that you see on the schematic that shows the secondary circuit are probably on a different subassembly. At least they better be!

[plexi50]

What's the deal with W14 and W17 appearing on the primary and secondary connections?

The W14 and W17 that you see on the schematic that shows the secondary circuit are probably on a different subassembly. At least they better be!

Yes they are different board assemblys. I am ready for more testing. Board and all connectors soldered solid and strong. Filament PT back in place and wired up/

[plexi50]

Here is pic with both seperate boards having W14 & W17 connections

[plexi50]

Yes transformer 65760 is filament transformer and the one i am taking voltages on.

I dont know what has changed from the voltages i took yesterday showing:
W22 & W19 = 94 VAC
W18 & W20 = 0 VAC
W12 = 3.20VAC
W13 = O VAC

Transformer back in amp and wired up
Voltage taken across these points tonight. Im so tired i cant think straight. Done to much today but still at it.

W2 & W5 120VAC

W22 & W19 60VAC

W18 & W20 60VAC

W12 & W13 3.230VAC

I will follow your directions in the morning and test the filament transformer. I had the transformer back in and wired up before i read your post

[sluckey]

W22 & W19 60VAC

W18 & W20 60VAC

W12 & W13 3.230VAC

These voltages are exactly half what they should be. I think the dual primaries are connected in series and the applied line 120VAC will split evenly across the two primaries. This can only happen if the links are wrong or the transformer wires are connected wrong. You must use links 7, 10, and 11 for 120V operation. If the proper links are installed then you have the primary wires (W17 - W22) messed up.

Since you only have 60V (half what it should be) on the primaries, the secondary is correctly showing 3.2V (half what it should be). That means the transformer is probably good. Now just get the primaries straightened out.

[plexi50]

Ok i am going back over the links now.

[plexi50]

Steve all the links are correct. I found a pic online of the wiring colors to confirm how i have this one wired. It is the same as when i got it in. Shouldnt W17 white wire have 120VAC on it? I have 60VAC.

[Willabe]

I agree with Sluckey, you have the primaries in series and they need to be in parallel.  

Looking at the schemo in your 1st post if you look at the 3rd page, the 2 PT's in between them is a foot note box with numbers but no wire colors.

It reads; 115v: Fit  Lk1, Lk4, Lk5, Lk7, Lk10, Lk11.
(Edit: I forgot Lk11, sorry.)
Problem is it shows as drawn all links hooked up, they should have shown 3 different drawings, 1 for each wall input voltage, ie, 100v, 115v and 230v.

(It's drawn with shorts too because it has all 3 link setups drawn at once, bad, bad, bad drawing!)

Because you don't know the primary color code you probable will have to disconnect ALL the primary wires on both PT's and do a resistance check to find the 0, 100 and 115 legs/taps. Then you have to follow the foot note for 115v wall voltage and ONLY make those connections.

Unless someone has a better idea  that's what I would do. Unless you can find the wire color code somewhere, maybe Marshall would give it to you?


               Brad      

[Willabe]

You can't have Lk3 and Lk4 hooked up at the same time. Also you can't have Lk9 and Lk10 hooked up at the same time.                  


          Brad      

[Willabe]

OR you have 1 or more extra links hooked up and it's shorting out or doing something weird. There's a lot of strange possibilities with wrong links hooked up.            

That could be why 1 of the PT's was smoking hot.


           Brad    

[plexi50]

ONLY make those connections

Just what i have been thinking all along. Seeing the amp with all of the wires connected just didnt seem right. I mean if you are wired for 120VAC then you wouldnt have the rest of the wires for 230VAC operation connected on the board too. Im sorry if i have been giving you a hard time guys. My memory has been messing with me for the past 6 months pretty bad. I am forgetting the most simple things in an instant. Like how to spell CAT. Pull the ring skin off bologna and throw the bologna away standing there with the skin. Lol!!! Jeez*

I went to cook a corn dog and instead of cooking the corn dog i only put the mustard on the plate. But seriously i really thank all of you for the time and brain strain it takes especially trying to decipher a schematic like this with no wire color coding. The basics of the primaries shouldnt be this difficult.  It's very hard to concentrate when you start following the links which also link to other terminals as well. Thats when i figured out that it does not mean a wire must connect to that terminal as well.

You can't have Lk3 and Lk4 hooked up at the same time. Also you can't have Lk9 and Lk10 hooked up at the same time
Exactly what i have been thinking. But the schematic is messing with my head. I know Steve simple diagram is the right way it should be wired up for 120VAC. But then i have to refer back to the marshall schematic to make sure that i am not linked as well to 2-3 other terminal links that tie into other wires. I have to decipher the transformer voltages and then make the connections per link for 120VAC. I'll get it eventually.

[Willabe]

Seeing the amp with all of the wires connected just didnt seem right. I mean if you are wired for 120VAC then you wouldnt have the rest of the wires for 230VAC operation connected on the board too.

It's very hard to concentrate when you start following the links which also link to other terminals as well. Thats when i figured out that it does not mean a wire must connect to that terminal as well.

But the schematic is messing with my head. I know Steve simple diagram is the right way it should be wired up for 120VAC. But then i have to refer back to the marshall schematic to make sure that i am not linked as well to 2-3 other terminal links that tie into other wires.

Yep, that's what's screwy with Marshalls drawing. They know better too, especially with such a big amp and with all those links!      

They should have made 3 separate PT drawings, 1 for each wall voltage situation, 100v, 115v and 230v.

(Look at my edit 3 posts back, I forgot Lk11.)


            Brad      

[sluckey]

It reads; 115v: Fit  Lk1, Lk4, Lk5, Lk7, Lk10.

Well, you left out LINK11. That's pretty important!

Guys, don't let these links mess you up. The schematic simply shows all possible links. BUT NONE OF THE LINKS ARE IN PLACE ON THE SCHEMATIC. It's up to you to take a pencil and color the LINKS that will be used for 115VAC. Then it should be clear. Crystal! (my best Jack voice)   

Silvergun made a drawing where he boxed in RED all the LINKS that need to be installed. If it ain't boxed in RED, don't install it! See reply #29.

[Willabe]

It reads; 115v: Fit  Lk1, Lk4, Lk5, Lk7, Lk10.

Well, you left out LINK11. That's pretty important!

Yes thank you, I caught that and made an edit.   

The schematic simply shows all possible links. BUT NONE OF THE LINKS ARE IN PLACE ON THE SCHEMATIC.

Silvergun made a drawing where he boxed in RED all the LINKS that need to be installed. If it ain't boxed in RED, don't install it! See reply #29.

Ok, now I remember SG's boxed in red drawing, I'll go back and look at it.


            Brad     

[Willabe]

Sluckey, I went back and looked at both your drawing and SG's and FWIW, I agree they look right.

The schematic simply shows all possible links. BUT NONE OF THE LINKS ARE IN PLACE ON THE SCHEMATIC.

Ok, I see it now, because W10-W15 and W17-W22 are not connected to the PT primaries. I still say it's a screwy way to draw it up bit I guess they did it that way because the wire connections around the links are always there, maybe even traces on the PCB?


                    Brad     

[plexi50]

 

That sums it up! Never quit is what i say. The lunatic is in the amp! 

[SILVERGUN]

 

GREAT job of getting to the bottom of it guys!!!!

I'm just a little too timid to be pushing people I don't really know.....

plexi, it was a pleasure getting to know you here, and I've learned a lot about "how to" help someone.....sorry I left out a couple key words that could've made this easier on you

If it ain't boxed in RED, don't install it!

9 words that sluckey so eloquently expressed for me 

[plexi50]

SILVERGUN you have been a big help. Any info is better than no info. It has been a pleasure as well here and thanks again for your input. I emailed Marshall to see if they have a voltage spec method to there colored wires in this amp. In any case i am taking a day off from this beast and will sort out the primary wiring.

Sluckey, I went back and looked at both your drawing and SG's and FWIW, I agree they look right.

The schematic simply shows all possible links. BUT NONE OF THE LINKS ARE IN PLACE ON THE SCHEMATIC.

Ok, I see it now, because W10-W15 and W17-W22 are not connected to the PT primaries. I still say it's a screwy way to draw it up bit I guess they did it that way because the wire connections around the links are always there, maybe even traces on the PCB?


Yes i was looking at the board while i was re-soldering all the push on terminals. There are traces all over under the board that are linked to the links. This amp is Bi-Polar   

[sluckey]

I emailed Marshall to see if they have a voltage spec method to there colored wires in this amp.

Does that mean there are no identifying markings on the PT or leads, or connectors??? Nothing at all to tell you this wire connects to here???

Do the PT leads each have a separate terminal, or do the wires fit into a multi terminal connector that can only be plugged in one way?

I'd like you to pull the LT transformer and set it on the bench. Take several good pics that clearly show everything that is written on the body of the PT and the wires and the terminals.

This is probably not your case, but I have seen expensive transformers and big transmitting tubes that actually had the wire labels stamped into the insulation of the wires. Rather than seeing AWG bla bla, the writing on the wire told you where it should connect.

[plexi50]

No voltage info on FT other than part number. I pulled back the rubberized bottom pad but nothing there either. No markings or numbers on wire connectors. Wire gauge and 300 volt printed on wires themselves

[plexi50]

Connectors void of any numbers or letters, Camera battery charging. Trying to show the info on the wire itself

[sluckey]

What's up with the orange pics? We need to see the wire colors. Never mind for now though.

I can help you figure out which wire is which. Then you can connect them properly.  It'll take longer to read the instructions than it will to actually figure it out. 30 minutes tops  to get it hooked up on the bench if you understand what we will be doing. Wanna play?

[plexi50]

Yeah sounds good. Lets go for it. I am going to use a different camera from here out. Ready,Set,Go!

I know where the (3) Black wires connect. (2) are the filament wires to the fuse link and (1) is the (AC i believe)
I know where the (2) orange low voltage wires go
That leaves one of each: Brown / Gray / Red / White / Blue

[Willabe]

I'd isolate the pairs and 3x sets of the primary and secondary by resistance test.

Then to find the primary 3x set, ie, 0-100-115, do another resistance test. 100 and 115 will be closest together and 115 will be furthest from 0.

When you find the primary set you can carefully tape up the unused secondary wires and apply a low voltage to the 0-115 pair, say 1 to 10 vac to the primary and take a reading on the secondary wire pairs. That should tell you what's what.


           Brad      

[HotBluePlates]

Well, your pic shows (at least part of) the problem: Link 9 is connected (shouldn't be) and Links 10, 11 are not (should be). There may be others not depicted in the photo.

Cut all the f-ing links. Take bare wire and jumper 1, 4, 5, 7, 10 and 11 and no others. Then you should be good (assuming you can put the LV transformer back like it was).

[plexi50]

Well, your pic shows (at least part of) the problem: Link 9 is connected (shouldn't be) and Links 10, 11 are not (should be). There may be others not depicted in the photo.

Cut all the f-ing links. Take bare wire and jumper 1, 4, 5, 7, 10 and 11 and no others. Then you should be good (assuming you can put the LV transformer back like it was).

Filament transformer wires measured so far
:
Brown & Black = 1 ohm
Brown & Gray  = 6 ohm

White & Red = 1ohm
White & Blue = 6 ohm

Red & Blue 6.7 ohm


Links 1-6

[Willabe]

Just in case you're still having trouble seeing it,,,here's the connections that you need to verify

I don't think the links do any thing as long as you only hook up the right wires where they go.

Guys, don't let these links mess you up. The schematic simply shows all possible links. BUT NONE OF THE LINKS ARE IN PLACE ON THE SCHEMATIC. It's up to you to take a pencil and color the LINKS that will be used for 115VAC. Then it should be clear. Crystal! (my best Jack voice)    

Silvergun made a drawing where he boxed in RED all the LINKS that need to be installed. If it ain't boxed in RED, don't install it! See reply #29.

Here's SG's highlighted drawing link, link pun intended.      

http://www.el34world.com/Forum/index.php?action=dlattach;topic=16480.0;attach=40709

             Brad    

[sluckey]

You told us several times that the links were right. They ain't.  Also, of the links I can see, I'm guessing you have had a wire strap soldered in every link. If Marshall had wanted all of them connected, they would have just etched solid traces on the board. Hopefully you didn't kill the transformers. Put the transformer aside for a few minutes and fix'em now. If you don't understand about the links then take another pic showing all 12 links and I'll draw them in for you.

Here's a pic showing correct links for the few that I see...

EDIT... Added the rest of the fixed links.

[Willabe]

I said this earlier that the links in the schemo would cause a short.  

HT and LT are the same so I didn't color both, short in purple, sends + to ground.

You can't have Lk3 and Lk4 hooked up at the same time. Also you can't have Lk9 and Lk10 hooked up at the same time.

              Brad              

[plexi50]

Heres the back of the board with traces going to links.
Pic #1 is Links 1-6
Pic"2 is Links 7-12

Ok i am working off your info now.

[sluckey]

I've just analyzed your links. Your photos show links 1, 3, 7, and 9 installed. Well, that's strapped for 230V. But you're line voltage is only 120V. That's why your filament voltage was only half what it should be.

Solder the six jumpers across the links we've been telling you to use. Look at my fixed pics. Then put the LT back in the chassis and connect the wires like they were.

[plexi50]

I've just analyzed your links. Your photos show links 1, 3, 7, and 9 installed. Well, that's strapped for 230V. But you're line voltage is only 120V. That's why your filament voltage was only half what it should be.

Solder the six jumpers across the links we've been telling you to use. Look at my fixed pics. Then put the LT back in the chassis and connect the wires like they were.

Ok im going to work now.

[sluckey]

You can't have Lk3 and Lk4 hooked up at the same time. Also you can't have Lk9 and Lk10 hooked up at the same time.

He didn't. He only had links 1, 3, 7, and 9 installed when he took those pics. That's the configuration for 230VAC operation.

[plexi50]

Links finished. Look at pic's. Connecting wires now back as they originally were/