Marshall VBA 400 Bass Amp / No Power

[plexi50]

I have this monster of a Marshall bass amp that has no filament voltage. No B+ as well. I am checking to see that it is wired for 120 A/C.
The pilot light is working. Can someone explain the toridal power transformers to me? I have the schematic. No color code wiring scheme to go by

[eleventeen]

In general, a torioid is no different than a conventional tranny, just a different form factor based upon the superior magnetic properties of the toroid. The pilot, to me, looks like it runs off the filament voltage so that's sort of odd. With power off, just check continuity across windings as you would on any other suspect tranny. Does it look like it was messed with? (I'm just asking questions to jog your thinking)

Somewhat puzzled as to why you would suspect a different primary voltage. Did it not work at some point here in the US? Think someone changed it?

That sucker is a welder.

If the primary fuse is good, I would check any interconnect ribbon cables and the like. 

[plexi50]

Well the amp was shipped from England and bought as not working. It is factory marked 220 VAC on the main input panel. Most of the connectors seem very loose (wiggly). Could be my imagination.  It look very clean as new and un messed with. Fuse was blown when it came in. All screens and grid r's good

[SILVERGUN]

That sucker is a welder.

In my experience with welders, I have seen a lot of problems associated with the input links set incorrectly, or loose.....even from guys who swear that they know what they are doing....
Since you have issues coming out of both xfmrs,,,B+ and filament (confirm that after replacing fuses),,,,, I want to believe that your problem IS on the primary side
I cant tell from the schematic if the pilot light would still work if T (thermostat) was tripped

I'm just a scrub R+R guy, but I did stare at the schematic for a 1/2 hour  ......(long enough to notice the 12AU7 PPI CF driver tube  )

[PRR]

What does RL1 do?

I'm suspecting that it de-energizes the HT PT until a speaker is plugged in.

That does not explain no tube heat.

I still don't see any pilot light.

Links are vital!! While 117V on a 230V connection won't blow-up, there's ways to put those links that will short-out the power line.

You should find 117VAC *across* R2 when just plugged-in, across C6 when turned-on, and across C5 when HT is engaged (which needs RL1 pulled-in).

If it is "overheated", there is 117VAC *across* T (thermostat). These things can go bad (open). Also their lugs can lose contact. (Hacked a lot of these when I used to live with Mr Coffee.)

[SILVERGUN]

I still don't see any pilot light.

Is this it PRR?
Page 1 bottom left....seems to be in the heater path

[plexi50]

I will get back on this tommorrow. I'll check those voltages at the reference points given PRR.
I got food posioned by a fish sandwich. Yuk

Cant stay away from the amp/ Oh well. Here goes:

120VAC @ R2 1 Meg resistor 1.675 VAC across other side of R2 1 Meg
120VAC @ C6 when turned on / 1.725 VAC @ other end of C6
C5 3.92 VAC when Standby engaged. 1.495 VAC on other side of C5
 

[SILVERGUN]

120VAC @ C6 when turned on / 1.725 VAC @ other end of C6
 I think you should be seeing the same 120VAC at C5 that you see at C6 with the standby switch engaged.....maybe jumper/bypass RL1b?

I would also check IR1, which I believe to be a thermistor (current limiting)......should measure approx. 2.5ohms on it's own (?)

PRR, I'm just throwing this stuff out there in an attempt to learn, with your guidance.....please bear with me plexi, I think I'm doing Ok....if nothing else, my "help" should make for a good laugh.......
good luck sir, it's off to the NYE celebration with my wife    

[plexi50]

IR2 thermistor is good and i have 120VAC on both sides of it
1R1 thermistor 3.80VAC and across 3.11VAC

Continued:
W2-W3-W4-W7 all have 120VAC on them

W6 has 3.56VAC when standby switched on / RL1B i am looking at now

[SILVERGUN]

1R1 thermistor 3.80VAC and across 3.11VAC

wait for PRR to confirm/ deny....but I'll put this out there
If my value of 2.5 ohms for that thermistor is close to correct, then you are passing approx. 1.2 amps through IR1?  (@3.11VAC drop)


I'm still tying to figure out where W26 , W27 connect....

RL1a (coming off of W26 @ TR1) is our coil for RL1 (b).....right?
(maybe a bad TR1?)
If you bypassed RL1b contacts you would get 120VAC through IR1 to C5,,,,,and therefore have your B+

Are you checking preamp tubes (DC) or power tubes (AC) for filament voltages?.....(switch your meter?)

sorry plexi, just random thoughts while I wait for my wife to "get ready"

[plexi50]

Oh no, all random thoughts are more than welcome. Thats where we have to start anyway. Your a big help in me confirming the transformers health. I have thought about jumping W7 RLB1 (120VAC) over to W6. But i need to see some heater filament voltage first i believe. I think i have to have RLB1 voltage over to W6 to make the heater filament voltage complete and working. Look at W14 & W17.

I have 3.20 filament voltage at W17. I now need to see 3.2VAC +- on the W14 terminal. That would happen if i jump RL1B W7 to W6.
But i want to wait yet for more input before i fly blind and try this. What if RLB1 is shorted or something. I dont want to make matters any worse.

[SILVERGUN]

More random thoughts....
- RL1 is a simple make/break relay.....with 60V fed through coil RL1a,,,, RL1b should close and complete our 120VAC to W6 (we agree).......

- W26 is just a shared ground path and W27 is our supply V for that relay, and I have to assume that it is fed off of the xfmr that isn't controlled by the relay.......so you should see 60V(ish) (if TR1 is OK) @ that coil (RL1a) with mains switch engaged
-That coil needs a path to ground to work ...... the next thing I would look at is the shorting jack speaker connectors, which serve as the path to ground in that speaker switching circuit PRR mentioned earlier...........right?
- Without a speaker plugged in(or a faulty jack / contacts), the coil won't energize

- If you jumper RL1b contacts, you will just be bypassing the 'speaker plugged in' protection circuit (and see if the amp works)

- At that point you should know either relay coil / contacts is bad, speaker jack is faulty, or TR1 is bad........heck, you might be able to just switch speaker outs and solve the mystery .....just try plugging into the other speaker jack

Good luck sir, and Happy New Year!
I'm glad to have the chance to get these thoughts out (while everyone else is enjoying the holiday), and possibly be corrected or confirmed, and possibly learn something.

[SILVERGUN]

I don't like to go back and edit posts...but there is something I would like to let PRR know so he doesn't think I am a knucklehead.....so instead of editing the post to "make myself right", I'll just explain....

In post #5 I pointed out the pilot light....but I only found it right after PRR said he didn't see it either...sooooo, of course it wouldn't be lit if T was open........I should have written that then

I feel better now  

Except, I'm still upset that there is no designation for where W26 (or W27) originates....I hate missing puzzle pieces ...can you trace it out physically and tell me where it goes?

[PRR]

> I hate missing puzzle pieces

I hate the whole dang drawing. MUCH too messy and broken-up.

I also do not like builds which have more connectors than parts. Both for clarity, and because connectors go bad a LOT. IMHO this is a build-only design, not repairable (not any sane way).

I think you are doing better than me.

[Willabe]

I think you are doing better than me.

     Well there ya go SG, your doing good.

I was looking at it too, very messy and very chopped up alright.


             Brad    

[SILVERGUN]

I think you are doing better than me.

     Well there ya go SG, your doing good

Yeah,,, I guess  ,,,I kinda wish he woulda said that last year....it's gonna be hard to top that in 2014 

So plex,,, check the speaker jack switching contacts, and verify 60V @ RL1a with the mains switch engaged and a speaker plugged in

I wouldn't hesitate to jump out RL1b.....typical relay failure is either bad coil or points stuck closed

If you're 100% sure that you've got the input jumper links correct, there should be nothing scary about it.........to test further, of course

I would be much less likely to believe that the xfmr is bad, unless somebody did something really stoopid

[Willabe]

I kinda wish he woulda said that last year....it's gonna be hard to top that in 2014 

 

[plexi50]

I think you are doing better than me.

     Well there ya go SG, your doing good

Yeah,,, I guess  ,,,I kinda wish he woulda said that last year....it's gonna be hard to top that in 2014 

So plex,,, check the speaker jack switching contacts, and verify 60V @ RL1a with the mains switch engaged and a speaker plugged in

I wouldn't hesitate to jump out RL1b.....typical relay failure is either bad coil or points stuck closed

If you're 100% sure that you've got the input jumper links correct, there should be nothing scary about it.........to test further, of course

I would be much less likely to believe that the xfmr is bad, unless somebody did something really stoopid

Ok i will verify the 60V @ RL1A with the mains on and speaker plugged in tommorrow. I have it off my bench right now.
Man this thing is heavy!

[plexi50]

Ok i have it back on the bench. Back in a few minutes------------

[plexi50]

RL1b is now jumped and C5 has 120 VAC with standby engaged

No A/C voltage at RL1a / D5 or TR1 with speakers connected

I do have -27.46 VDC at these points though  

[SILVERGUN]

How about filament or B+ voltages?

No A/C voltage at RL1a / D5 or TR1 with speakers connected

Should be DC there....and 27.46 is a good sign

[plexi50]

No filament voltage on W14. Only on W17 to power tubes pin 2
No preamp filament voltages at all
No B+ volltage. Just 100VAC from the RL1b jump with standby on

And i thought the TSL 2000 was the worst design of all time. At least the TSL has a schematic you could read

[SILVERGUN]

No filament voltage on W14. Only on W17 to power tubes pin 2
No preamp filament voltages at all
No B+ volltage. Just 100VAC from the RL1b jump with standby on

OUCH......now I'm in trouble...

Input links, input links, input links.......that's all I got

I just don't want to believe the xfmr is bad  

What do you get if you measure AC volts from W17 to W14?
What do you get across IR1 now?
Check F1 fuse on secondary, labeled T6.3A....

If you read the part I erased you'd know I'm obviously distracted by the Flyers game.....sorry about that one   

[plexi50]

I just don't want to believe the xfmr is bad
Me neither!


What do you get if you measure AC volts from W17 to W14?
3.200 VAC

What do you get across IR1 now?
1.65VAC & 20.20VDC

Both thermistors are good @ 2.0 ohms and are passing current

Maybe marshall has a service schematic? It looks like this schematic is one big puzzle.

[SILVERGUN]

Can you assure me that the input links are perfect?,,,so I can stop obsessing about them,,,sorry to ask again
Now that you're seeing 120VAC @ C5, it has to get through the correct links to make the magic happen on the secondary.....

I'm afraid that if they are set right, and were still scratching our heads,,,,this may be bigger than me

Maybe marshall has a service schematic? It looks like this schematic is one big puzzle.

Yeah.......unfortunately I don't see anything on the net

[SILVERGUN]

What AC volt reading do you get from:
W15 to W16?
W15 to W23?
W16 to W23?
W6 to W7?
W12 to W13?

I hate failing.....If I had it in front of me it would be tough to walk away....

If the links are right and you've got 120VAC through to C5 and C6, the secondary AC voltages "should be' fairly obvious

Good luck man,,,,I feel for you 

[plexi50]

Can you assure me that the input links are perfect?
No! Thats why i wanted to check the wiring to make certain that it is wired for 120VAC instead of 220VAC EURO

I check the fan on low and high speeds. It seems to rotate very slowly on low speed. Like i almost have to give it a push with my finger to get it going. High speed is faster but doesnt blow any hardcore wind or sound like it is hauling azz

I shouldnt assume this but it did come from England and so i need to confirm the voltage mains wiring. This is going to be a long haul

Be right back with those voltage readings/

[plexi50]

With Standby Engaged/

W15 to W16 - 119VAC

W15 to W23 - 119VAC
 
W16 to W23 - 0VAC - 3.20VDC

W6 to W7    - 0VAC - or VDC

W12 to W13 - .045VAC

No i know what you mean. Sometimes the obvious slides right by me. All your thinking has been a big help
The schematic is almost Greek to me

[SILVERGUN]

Can you assure me that the input links are perfect?
No! Thats why i wanted to check the wiring to make certain that it is wired for 120VAC instead of 220VAC EURO

I check the fan on low and high speeds. It seems to rotate very slowly on low speed. Like i almost have to give it a push with my finger to get it going. High speed is faster but doesnt blow any hardcore wind or sound like it is hauling azz

I shouldnt assume this but it did come from England and so i need to confirm the voltage mains wiring. This is going to be a long haul

Be right back with those voltage readings/

Yup,,, this all points to those jumper links being incorrectly set....
The fan spinning slowly means it's not getting full voltage...the missing voltages, low voltages, relay not energizing......all makes sense

What do the links look like? (pics?)...I've searched for pics but cant find any, and no help from Marshall either

I'm pretty confident that if we get that straightened out, it's gonna do it  

The schematic is very similar to what I see in welding machines, so it doesn't bother me that much......those links have caused perfectly intelligent grown men to blow up perfectly good $3000 welding machines........that's why I keep going back to that......I'd be thrilled to know I actually helped you figure this out  

[SILVERGUN]

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

[plexi50]

Checking now/

[plexi50]

Ok all links are confirmed and wired correctly! Interesting and curious possabilities!

[SILVERGUN]

zzzzzzzzzzzzzzzzzzzzz......

I'm hoping to wake to news of your success.....
it will take the sting off of 6 fresh inches of snow and a Flyers loss

[SILVERGUN]

No! Thats why i wanted to check the wiring to make certain that it is wired for 120VAC instead of 220VAC EURO
Sorry man,,,I don't know why I thought we were past that......I had assumed that we had originally found it set for 220VAC and at some point you had switched the links around to be correct for 120VAC  

Ok all links are confirmed and wired correctly! Interesting and curious possabilities!

Does that mean that they were wrong and you now changed them and got them right?
Or were they set right all along?

Kinda like an Abbott and Costello skit at this point  
Abbott & Costello: "Two Tens for a Five"

[plexi50]

No they were set right all along. I just got confused looking at all the links. There are so many links. There are some that have the same link numbers on the power supply capacitor board as the back board attached to the rear of the chassis where all the links connect. Im all linked out. I'll get some pics up later today.

[Willabe]

"Here, here's 2 tens gime back my 5."


           

[SILVERGUN]

No they were set right all along. I just got confused looking at all the links.

Well, that blows.....that was the only hope I had  

I don't think there's any good explanation for why were not seeing proper secondary voltages,,,,,except bad xfmr (s)

I would triple check those links, and then triple check them again,,,,,,but that's just because I have a problem.....I don't believe what my eyes tell me sometimes  

[plexi50]

I don't believe what my eyes tell me sometimes

Isnt that the truth.
I will go back and look at it later. I know it's linked to the links of the link that goes to the links that link the links to the links that link the whole dam thing up* 

[Willabe]

I know it's linked to the links of the link that goes to the links that link the links to the links that link the whole dam thing up*  

      

Your a brave man and I believe you'll fix it but man what a pain.


           Brad     

[plexi50]

Your a brave man and I believe you'll fix it but man what a pain

I dont know about that Willabe. Im getting tired of amps made of left over parts

[Willabe]

Im getting tired of amps made of left over parts

              

Yeah I don't blame you, I don't think I'd want to poke around in there.

But we've all seen you fix a (good?) number of PCB amps among other amps that were strange also as in finding some weird problem. You always fix it in the end though.


                Brad     

[plexi50]

Thanks Brad. We have no other choice but to live and learn in this business. What the heck it's fun to (i think?)

[SILVERGUN]

What the heck it's fun to (i think?)

I was having fun, until I realized I wasn't going to WIN  

I'd still love to see pics of the monster that got me......
I'll hang em up on my wall to remind myself that I'm not as smart as I thought I was.......(my wife is right,,,again)
AND...
If I crack open an amp and there's a PC board in it,,,,close it up, give it back, and get back to doing something constructive with turrets  

LIFE'S TOO SHORT

If you must continue on......I'd probably mark and disconnect all secondary connections and check voltages that way....
It's the only way to confirm the xfmr is bad.......... (   ,,,,those toroids are pretty robust).....maybe a short on the link board?

 

[Willabe]

...I'd probably mark and disconnect all secondary connections and check voltages that way....
It's the only way to confirm the xfmr is bad.......... (   ,,,,those toroids are pretty robust).....maybe a short on the link board?

+1

[sluckey]

I have this monster of a Marshall bass amp that has no filament voltage.

Do you still have no filament voltage?

If so, use this drawing to fix it.

[plexi50]

I have this monster of a Marshall bass amp that has no filament voltage.

Do you still have no filament voltage?

If so, use this drawing to fix it.

Fantasticola Steve. No i have no filamnet voltage yet. Been doing satuday house work and should i say it (laundry)
Will get on it very soon and report back with my findings. Thanks again all of you. Maybe i should throw the marshall in the washer too?

[Willabe]

Maybe i should throw the marshall in the washer too?

     

[plexi50]

Threw in washer. Results

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

I stood up an noticed heat coming from the top of the chassis. 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. I use a small fuse block with fuse to bypass the thermal switch. It gets the panel out of my way at the same time. Bad Transformer?

What is the big TT function and what is the smaller TT function. I know i can look and see but im lazy  

[sluckey]

I know i can look and see but im lazy

Well, in that case, maybe you should just throw it in the washer.   

[plexi50]

I know i can look and see but im lazy

Well, in that case, maybe you should just throw it in the washer.  

  I know. Ha! It is the transformer that supplies the mains voltage for the power supply and heaters. Man it's been over an hour and it is still hot to the touch. I removed the mounting bolt nut pulled it off the chassis.  I have not removed the wires yet until i get good pic's. I hope the new one has the same color coded wires. Have to call a place in Norwich England Monday. I will try Patrick @ MM first