DBX 118 PSU

[Walrus]

Sorry, mistake in my last post, it should be OA2, not OA4.

 

[Studiogearlover]

Sorry, mistake in my last post, it should be OA2, not OA4.

yepp...but the more I plug the unit in the more problem I am getting...now the leds started to blink like a railway crossing and I have not touched the unit ..hahah...oh my god what is goin on?

Did some further measurements...

at C1 +ve I am measuring 70 VDC. ( wonder how? or why?)

at the diodes...

CR1 also  70 VDC/ 30VDC
CR2 also 30 VDC/ 0 VDC

At the power transformer I measure 10,5 VAC on each node to ground.

At the R45 which is the calibrating resistor, the lowest voltage DC i could dial is 20VDC. It does not go lower than that.

I think I can conclude:

PSU works fine
OA2 ( pin1 to pin 8 measuring 24VDC)
R45 resistor works

CR1 and CR2 diodes...maybe the guilty ones?

 

[Walrus]

With the unit turned off and disconnected from the mains, with your DMM, can you measure the resistance from OA2 pin one to connector P1 pin one or P2 pin 1 or P3 pin 1 and also to output connectors earth. They should all be connected to each other and show zero Ohms resistance (or very close).
If OA2 is broken, then it's output may be at the same potential as the output of the 723 regulator, hence why you are getting odd readings. Without this nominal "zero point" at Pin1 of OA2, then you can not measure from any chassis earth and expect a rational reading.

 

[Studiogearlover]

With the unit turned off and disconnected from the mains, with your DMM, can you measure the resistance from OA2 pin one to connector P1 pin one or P2 pin 1 or P3 pin 1 and also to output connectors earth. They should all be connected to each other and show zero Ohms resistance (or very close).
If OA2 is broken, then it's output may be at the same potential as the output of the 723 regulator, hence why you are getting odd readings. Without this nominal "zero point" at Pin1 of OA2, then you can not measure from any chassis earth and expect a rational reading.

Measured it... all of them  0.5 Ohms...

 

[Studiogearlover]

Okay....

Removed all the other pcbs... the RMS, the VCAs...justin case not to damage these

Considering that the PSU is OK. Considering that the  issue is around the C4/ CR2, CR1 and the OA1 I should start and replace all of these I reckon.

What else could go off considering that the resistors aren't drifted and I can not get a 12 VDC out of the R45?

Either the diodes, or the OA1. ( I have replaced the C4 with new electrolytics already)

...and...I have a several RC4559Ns to play with (which I did) for OA2. I have 4 RC4559N and the original RC4558ND in hand and all of them are giving me the same result.

Would you agree?

 

[Walrus]

What DC voltage do you have across C1 +ve -ve, and then across C2 +ve -ve?
Also what voltage do you have across R2 and across R5?

 

[Studiogearlover]

What DC voltage do you have across C1 +ve -ve, and then across C2 +ve -ve?
Also what voltage do you have across R2 and across R5?

Hey !

C1      47,6 VDC

C2      47,6 VDC

R2    46 VDC

R5    24 VDC


would you reckon that the diodes CR1/ CR2  or the actual OA1 is failing?

 

[Harpo]

C1      47,6 VDC
C2      47,6 VDC

So raw DC voltage across C1/C2 would be 95.2 V. Not possible with an assumed  12VAC transformer and voltage doubler in front.

would you reckon that the diodes CR1/ CR2  or the actual OA1 is failing?

More likely the battery in your multimeter is low, giving such numbers ...

 

[Studiogearlover]

So raw DC voltage across C1/C2 would be 95.2 V. Not possible with an assumed  12VAC transformer and voltage doubler in front.
More likely the battery in your multimeter is low, giving such numbers ...

hey.... measured it with my second DMM, and they are the same.

Both DMM has new 9V batteries...

 

[Walrus]

As Harpo says, those numbers do not make sense.
What make is your DMM?

 

[Studiogearlover]

As Harpo says, those numbers do not make sense.
What make is your DMM?

two DMMs can not go wrong i think the fault maybe myself...

measured across the cap's and the resistors...each sides ... the readings are correct

measuring the same to GROUND ( lets say the pin1 on OA2) it is a different story..but I have posted this measurements in one of my previous post

so here it is

C1 +ve to Ground 70VDC
C1 -ve to Ground 22 VDC

C2 +ve to Ground 22 VDC
C3 -ve to Ground is 0 VDC

R2  24 VDC on one side, 70 VDC on the other

R5 24 VDC on one side, 0 VDC on the other

this would makes more sense right?


if you

 

[scott2000]

Wow this thread is a brain bender..... following with interest

So what is the voltage measuring from C1+ to C2-?

Sorry if I missed it.......


maybe you could add in the voltages you are getting into the schematic so it's all in one place to glance at???

 

[Walrus]

You don't have a 110v unit connected to 240v mains do you????

Quote:  R5 24 VDC on one side, 0 VDC on the other

This either means R5 is dissipating 57.6 Watts, or Pin 1 on OA2 is connected to Pin8. i.e. this chip is short circuit internally.
But I think you said you had changed this chip?

 

[Walrus]

Wow this thread is a brain bender..... following with interest

So what is the voltage measuring from C1+ to C2-?

95.2 volts!!!

 

[Harpo]

Any chance your meter was set for reading AC volts instead of DC volts and you missed the sometimes tiny 'm' in front of the 'V' for a 95mV ripple readout?
If your numbers were for real, you'd noticed the strange shape of the 25VDC rated caps and the 40V abs.max input at the 723 vreg. These parts most likely wouldn't look the same or be in the same location when kicked in the butt with a 95VDC feed.

 

[Studiogearlover]

95.2 volts!!!

OK...guys... thanks so much for your help really and I do apologise being a PAIN !


My 220/117 converter was failing .....((  checked it with my DMM and it gave my really way above readings and these were shifting up and down...!

Swapped this with my other one, a much bigger/ better 200 to 110VAC step down converter which has a correct VAC coming out if it.


let's do this again:

1. C1 +ve 30 VDC  -ve 9 VDC

2. C2 +ve 9 VDC  -ve  -12 VDC

3.  C4 +ve 12 VDC  -ve -12 VDC

4. R2  12 VDC and 30 VDC

5. R5  12  VDC and the other end is 0 VDC


These are absolutely correct measurements. Testes with both DMM

uuuuh.....sorry guys again...i did not know that the traveller step down converter is failing....

wonder what did I damage with this....

 

[scott2000]

so what's the problem again???

 

[Studiogearlover]

so what's the problem again???

;D

above threshold light constantly on.... switch doesnt respond... however in the last few days with my "trials" these lights were behaving differently....sometimes both were flashing ....sometimes none...sometimes only the "below" threshold was on constantly...

now the red is on constantly with no audio passing thorough ...

 

[scott2000]

Do you have a way to test caps?

 

[Studiogearlover]

Do you have a way to test caps?

yes..l have the PEAK Atlas esr + tester.

So far, all the electrolytic were replaced at the power stage. The two tiny blue tantalums I am suspecting this since the beginning...but one reads fine (c13) the other one reads leaky/ in circuit (C11) ...

this could be the source of the issue but I have got carried away at the power stage (as you've seen it  ;D ) .....