Drip Opto 6 LA2A - Low voltages across the board

[furn1979]

Hi!

My Opto 6 has been acting up lately. It'll work fine until a little power dip seems to occur within the unit... my meter lamp will dim, meter will dip a little and a slight hum can be heard in the audio signal.

Also, I can sometimes hear a slight creaking sound from within the compressor itself... maybe from the power transformer (Hammond 369JX) but I'm not quite sure. Wiring has been checked many times.

I'm measuring lower than expected voltages across the board.

At secondary #1: 547 VAC (normal)
At secondary #2: 6.5 VAC (normal)
At filter caps (275V): 196 VDC
At R13 (134V): 93.5 VDC
At TP 1 (110V): 73.7 VDC

Aren't these figures lower than normal? Where should I look?

I used diodes in the power section (checked them, they're fine).

Thanks!

 

[PRR]

Link to schematics and docs?

Tube or diode rectifier?

What gets hot when voltages sag?

 

[furn1979]

Link to schematics and docs?

See manual attached.

Tube or diode rectifier?

Diodes

What gets hot when voltages sag?

Nothing seems to get physically hot.

 

[scott2000]

Kinda like an Ikea manual......

wow....6x4 rectifier too?? what are the diodes doing??? you have a choice???

 

[mjrippe]

Sounds like filter caps going south to me.

 

[scott2000]

Would the dropping resistors create issues if going bad too???

 

[furn1979]

Kinda like an Ikea manual......

wow....6x4 rectifier too?? what are the diodes doing??? you have a choice???

Yep. Went with diodes, as the originals were.

 

[scott2000]

Ah right....I see that now....Pretty cool.....

What power are you using for your lamps??? That comes from the 6.3 from the hammond as well??

 

[furn1979]

Ah right....I see that now....Pretty cool.....

What power are you using for your lamps??? That comes from the 6.3 from the hammond as well??

That’s correct.
No DC heater on that model.

 

[moamps]

First, confirm that the red/yel wire from  power transformer (CT wire) is connected to the "power ground" pin on the board.
Then measure DC voltage on both side of R16 and 29 referenced to the power ground pin and post it here.

 

[CJ]

if no heat or exploding capacitors, then t sounds like you lost a phase of the pwr xfmr,

since you measure good on the secondary, the phase loss would have to be at the diode cathode junction, possibly a solder joint or fried trace, measure DCR between the two diode cathodes (unit unplugged and caps drained)

if no joy, try pulling the 12BH7 and measure B+ voltages,

if no luck, give it the chop stick test (mechanical problem) tap the chassis with a pen or pencil and see if the meter jumps,

 

[furn1979]

First, confirm that the red/yel wire from  power transformer (CT wire) is connected to the "power ground" pin on the board.
Then measure DC voltage on both side of R16 and 29 referenced to the power ground pin and post it here.

CT Wire to ground, confirmed
Across R16 = 194VDC and 147 VDC
Can't seem to find R29 (?) Where should it be located? Which value?

Not all resistors are numbered on the board/schematic.

Thank you for your help

 

[furn1979]

if no heat or exploding capacitors, then t sounds like you lost a phase of the pwr xfmr,

since you measure good on the secondary, the phase loss would have to be at the diode cathode junction, possibly a solder joint or fried trace, measure DCR between the two diode cathodes (unit unplugged and caps drained)

if no joy, try pulling the 12BH7 and measure B+ voltages,

if no luck, give it the chop stick test (mechanical problem) tap the chassis with a pen or pencil and see if the meter jumps,

Will begin these tests right now.

On the scope, the signal at the rectifier's diodes cathodes looks like this (see photo attached)... I'm guess my problem's here right?

 

[scott2000]

CT Wire to ground, confirmed
Across R16 = 194VDC and 147 VDC
Can't seem to find R29 (?) Where should it be located? Which value?

Not all resistors are numbered on the board/schematic.

Thank you for your help

R29 is probably under R28 (4.7k 2w) .....you may have already posted one side value 196v....... at least if it's going by the original schematic

 

[furn1979]

R29 is probably under R28 (4.7k 2w) .....you may have already posted one side value 196v....... at least if it's going by the original schematic

So across that 4.7k 2W, I'm getting 247 VDC and 194 VDC

 

[scott2000]

Definitely low on that..... should be around 350 instead of 247 ???

have you tested filter caps???diodes??

pulling the tube CJ said...???

So across that 4.7k 2W, I'm getting 247 VDC and 194 VDC

 

[furn1979]

ok... so I'm only half-rectifying, although my 1N4007 test ok... I'll install brand new ones and see how it goes.

 

[furn1979]

So I didn't have a pair of 1N4007 around BUT, I have a 6X4 tube and socket.

Installed it and now measuring this signal at the output of the tube (see picture attached).

Still only rectifying only one phase... is my power transformer secondary out? I'm still getting 549 VAC on that secondary.

 

[scott2000]

I don't think so??? But I'm not the one to know.....

Your transformer secondary is a bit high .....is that  because it's 500v rating is at 100v primary ???  No mention  in the guide of this???

 

[moamps]

Installed it and now measuring this signal at the output of the tube (see picture attached).

If the measuring channel on the scope is set to AC, turn it to DC, and
if the measuring channel on the scope is set to "invert",  please turn it off.

Switch the power off, disconnect the secondaries from the board (keep CT connecting to power ground) and measure the resistance using a DMM of the each winding to the power ground. They should be almost the same. If it is true connect the secondaries back, turn the transformer on and measure waveforms at the secondaries connections referencing to power ground. Scope probe gnd should be connected to the power ground. Place pictures here (downsize them to cca 800 pixels). Write the vertical setting of the scope channel.