I need help to check my voltages on my La2a...there is not audio....

[Rufus]

hello my La2a is not processing any audio...a friend told to check the voltages...I had done a lot of readings of people posting their voltages  to troubleshoot  their LA2As...how they do that?  the internet has a lot of videos on how to check voltages on a AAA battery and other instructions on how to find a faulty component on a broken TV (I whish it was that simple but its not) I  really need help on how  to check the voltage on the B+ ,v1,v2 ,v3, and V4 ...where do I need to put the needles of my multi meter? for  example if I want to check my B+; I  put one  needle of my multi meter on top of the actual B+ but where do I put the other one? the common sense told me put it  where the the actual current  is coming from originally into the power supply,,but all I get its a crazy oscillating reading  that goes from  zero to 300volts????  is there a section here in GroupDIY where I can learn how check these voltages myself?

I am supposed to compare the below reading with my readings
correct voltage list:
B+: 275v 
pin1: 115v 
Pin3: 1.2v ( )
Pin6: 120v
Pin8: 1.1v

V2:
pin1: 100v (87.1v)
Pin6: 220v (195.1v)
Pin8: 98v

V3:
pin1: 105v
Pin3: 0.75v
Pin6: 105v
Pin8: 0.75v

V4:
pin2: 7v
Pin5: 110v
Pin6: 125v

 

[AusTex64]

I hope I don’t hurt your feelings when I say this, but say it with sincere concern. Perhaps find a friend that knows some things about tube guitar amps or gear to give you a lesson. There are lethal voltages in the box you’re poking around in.

But to answer your question, the black probe goes to ground. Meter needs to be set to AC or DC voltage depending on where you’re measuring. The LA2A schematic will tell you where the points are. Tube data sheets will tell you what pins are which. B+ will be DC voltage. Is your unit on a PCB or point to point?

Finally, be sure all the tubes are glowing orange and warm. You’ll get no audio without heaters working.

 

[scott2000]

I was too scared to even answer......

 

[Rufus]

guys thanks for your concern, I will be very careful...

woa...my B+ reads 244volts (its too low) it should it be around 275v...the unit is on a PBC; I know where each part is located in my PCB and also now which pin to check for but I was not sure where to put the black prove but  now I now (thanks!!!!) its all AC only my heater are DC..all the tubes are glowing orange and are definitely warm ...this is very good  information from you: " I have no audio because my heaters are not working..I will check into it...thanks!!!!

 

[Rufus]

my voltages reading...do they look OK?

Voltages list!
B+: 275v (242v)
V1:
pin1: 115v (111)
Pin3: 1.2v (1.9)
Pin6: 120v (113)
Pin8: 1.1v (0.97)

V2:
pin1: 100v (91.6)
Pin6: 220v (201)
Pin8: 98v (95.9)

V3:
pin1: 105v (78.9)
Pin3: 0.75v (0.75v)
Pin6: 105v (79v)
Pin8: 0.75v (0.75v)

V4:
pin2: 7v (5.7v)
Pin5: 110v (127.3v)
Pin6: 125v (103v)

 

[andyfromdenver]

Hi Rufus,
I’m willing to take on helping you. Just listen to all I say and execute it as such (for your safety).
And ignore people unless they are on my team, otherwise you’ll get conflicting or counterproductive input.
1.  You couuuuld mail it to me in GA and i’ll repair it for you. the $$ route.
2.  I need more help from you. what is the pcb. V1-4 means nothing to me. tell me or show me the schematic to show the designated tube.
3. print out or save the data sheets for each tube.
3.5. I need the specs on your transformers too.
4. NEVER put both hands inside your box, you risk death. Clip your black common probe to a secure chassis ground, and then put your non-dominant hand in your back pocket. wear shoes and don’t stand in a puddle. With your dominant hand holding the red probe, you can test points for DC voltage.
5. UNLESS you have filter cap draining resistors, your power supply caps hold high voltage and can deliver a nasty shock. An operational unit (powered on for a minute or so) will naturally drain these batteries some, but you need to be wary of that.
6. NEVER make changes or work on the unit while it’s plugged in. make sure it is unplugged and the pwr caps are drained.
7. I assume ZERO responsibilty for your safety or damage to your box. All info provided by me is used at your own risk and referencing any of my advice or replying to me acknowledges your agreement of this last point.

ok, this is my start. buckle up and gimmie that data and we’ll take it slow.

I have some other questions, has it ever worked? is this your build or something you bought? how confident are you in the pcb population? how good is your soldering?

ok! tbc
andy

edit in: if you feel 100% about the pcb population. you could have miswired or omitted a ground. we’ll explore all this.
but if you built this in haste (cuz it’s a badda$$ machine and u wanna make music). take a minute or 10, a few deep breaths and VERY CAREFULLY check off all the off pcb wiring to make sure it is all 100%. You may catch a wiring error or omission. I am hoping you will.
I have a guest coming this weekend and will be away some, but let’s take it slow and get your fatbox going.