Need help for my original 1176 maybe it's died

[jandoste]

Hey Guys,
I got a original UA 1176 and since yesterday it doesn't work I'm trying to find the problem but I can't... it doesn't see any signal and I didn't find any 1176 B serie schematic... Did you have this problem? and what can I do to find this problem? maybe I need to change Attenuator [ in ]? if I get it from Hairball that can I use it?
Thanks for any advice...
cheers

 

[zayance]

Hey Guys,
I got a original UA 1176 and since yesterday it doesn't work I'm trying to find the problem but I can't... it doesn't see any signal and I didn't find any 1176 B serie schematic... Did you have this problem? and what can I do to find this problem? maybe I need to change Attenuator [ in ]? if I get it from Hairball that can I use it?
Thanks for any advice...
cheers

Not much info to help out, beside saying it's not working anymore?
Don't change something before beeing sure it's faulty, you can check the attenuator with your Ohm meter.
What happened before it's not working? When did it stop? Did it stop working when powering on the day after it was working good?
Did you move the unit before? etc...etc...
Since it's a 1176, most problems and troublshooting could be made going with all the infos on the support threads...
Basic check would be, Power and if all is good, but since you say it doesn't pass audio i believe it powers up.
But i would still check that...
Second, any visual check? Is there some bad looking parts? Burned etc...?
Bad transistor maybe? a cold joint on the Audio XLR's? etc.. etc...
Trooblshooting is actually harder than assembly, and sometimes can lead to even more troubles, believe me, especially on old units...
Like moving things around, and those old cables don't like it at all, they get cut, and you put back all things, and it's worst etc etc etc...
turn around an hour, and spot that it's that freakin cable, and you get back to were you were, in one word FUN
An oscillo would be great to spot where your signal gets lost, as always...
But just a DMM can do, but need to know what's going on first :/...

Anyway i'm not a pro in that domain....but i think there is loads of infos here for you to find out where it comes
from, you need to be methodic, patient, and aware of what you're checking and doing, if you go blindly
you'll get lost and won't find your way out, write down what you've done for keeping track of what's been checked etc....
Some basic electronic knowledge is always welcome when trying to fix things...

Good Luck!

 

[0dbfs]

yes. much info here in the various threads.I think revB is the same as revA.

Does it power up?
Do you have +30V / -10V where appropriate?
Did something come loose? Can you use a chopstick/poker to make the fault intermittent?

And last but not least, pictures please!

Thanks and good luck!
-jb

 

[jandoste]

Hey Zayance,
Thanks man!

Not much info to help out, beside saying it's not working anymore?
Don't change something before beeing sure it's faulty, you can check the attenuator with your Ohm meter.
What happened before it's not working? When did it stop? Did it stop working when powering on the day after it was working good?
Did you move the unit before? etc...etc...

I meant the unit can power up but audio signal can't pass...
Yep, opened it before that I had a problem with two capasitors, I changed two of them and also a resistor than 1176 was working well!

Since it's a 1176, most problems and troublshooting could be made going with all the infos on the support threads...
Basic check would be, Power and if all is good, but since you say it doesn't pass audio i believe it powers up.
But i would still check that...

I am reading all 1176  troublshooting but I didn't find any solution.

Bad transistor maybe? a cold joint on the Audio XLR's? etc.. etc...

That's the big problem for me! how I can understand that if I got some bad transistors? oscilloscope can help me? [ I guess :]

Trooblshooting is actually harder than assembly, and sometimes can lead to even more troubles, believe me, especially on old units...
Like moving things around, and those old cables don't like it at all, they get cut, and you put back all things, and it's worst etc etc etc...
turn around an hour, and spot that it's that freakin cable, and you get back to were you were, in one word FUN

Since three days I'm not sleeping for finding this problem  

An oscillo would be great to spot where your signal gets lost, as always...
But just a DMM can do, but need to know what's going on first :/...

I will check it again with an oscillo...

Good Luck!

Thank! I think I need it

 

[jandoste]

Does it power up?
Do you have +30V / -10V where appropriate?
Did something come loose? Can you use a chopstick/poker to make the fault intermittent?

And last but not least, pictures please!

Thanks and good luck!
-jb

Hey Jb,
thanks for the reply...
Here, I changed the big resistor before R80 260K

Than C23 2200uF 50V here

and a bigger picture

When I try to see with an oscilo there is something wrong [strange] with the input Attenuator... but I'm not sure what's happen...
Thanks guys! I hope I will find the problem...
cheers

 

[BPJ]

Guys,

This is a currently-made UA 1176LN, not an old one.

Jandoste, you may want to reference a Urei Rev. D schematic.

~BPJ

 

[zayance]

Guys,

This is a currently-made UA 1176LN, not an old one.

Jandoste, you may want to reference a Urei Rev. D schematic.

~BPJ

I wasn't refering to "old" talking about his original UA version,
i was just tchit tchatting.....

 

[0dbfs]

R80 looks like it's maybe a dropping resistor for a lamp. C23 is probably a PSU cap. Seems like these would be unrelated to no-audio...
Anyway, you can probably make a fixed 600R pad of like -40dB out of a couple resistors or whatever and try to replace the variable pad with that to see if audio passes.

Cheers,
jb

 

[okgb]

Or just jumper across the pad and or xfmr , you may have to lower the signal level
if they are indeed the problem you may have to disconnect them from the circuit if
they are grounding out the signal , But with the schematic once you know it's hitting the board
start tracing stage by stage until you find out where it stops

 

[pucho812]

is it just me, or in the photos, does Q8 and Q5 look like they have burned up?

 

[jandoste]

R80 looks like it's maybe a dropping resistor for a lamp. C23 is probably a PSU cap. Seems like these would be unrelated to no-audio...
Anyway, you can probably make a fixed 600R pad of like -40dB out of a couple resistors or whatever and try to replace the variable pad with that to see if audio passes.

Cheers,
jb

Hey Jb,
I'll try that tomorrow... That is strange because  R80 is => 47,2V 
Thanks

 

[jandoste]

is it just me, or in the photos, does Q8 and Q5 look like they have burned up?

Hey pucho812,


I think that all transistors died   but not sure if Q8 and Q5  they have burned... but i think that  just in photo you are seeing that...
Q9
B:16.7 V    [schemo says 17.7V [ it's ok ]
E: -09.9V  [schemo says 2.96V [ bad ]

C 18: -3.30V    [schemo -> 3.5V]

R 36[1M]:-3.30V  [schemo 4.54V]

etc. etc.

So I have checked the unit with Urei Rev. D schematic and I don't have any right Voltage values  F%cq!!!  tomorrow morning I'll try... my bad!

Thanks guys for helping me!
Best regards!

 

[jandoste]

Hey Guys,
Do you know that R80 resistor value is 75R 3W or 250R 5W? I got two 1176 D shematics and I don't understand which one  has right value?
Thanks

 

[ibvee]

I have an original rev D here, with 75R. It seems earlier versions had 250.

However, as you seem to have a reissue, I can't say if that's the same for you.

 

[jandoste]

I have an original rev D here, with 75R. It seems earlier versions had 250.

However, as you seem to have a reissue, I can't say if that's the same for you.

Hey Ibvee,
Thanks man!
Do you know this resistor is for PS or Vu metre? I guess it's for PS's resistor?
Thanks

 

[okgb]

75R 3W seems familier from the Purple version , but it can't hurt having a higher wattage

 

[jandoste]

75R 3W seems familier from the Purple version , but it can't hurt having a higher wattage

Hey Guys,
Good news 1176 is working now  : : :  I changed R80 and put 82r 3W bingo! but I am not sure this value is enough? because now  it's very "hot"? what do you think about  if I changed it with 270r 5W?
and I think that I must calibrate it? can I use  mnat's calibration?

Thanks for all your great helps guys!
love DIY and Diyers
cheers 

Edit: I also changed Q2 and Q4!

 

[joe-electro]

R80 might not be your only problem.  You need to check the current running through that resistor.  Measure the voltage across the resistor, then use Ohm's law (I=V/R)  to calculate the current passing through it.  The current should not exceed about 135 mA.  If the current is too high, check the 10W zener diode to make sure it's not getting too hot. If it is, replace it.  And check the +30V supply to make sure it is within about 2% of 30V.  If it's not, replace the zener. Those things really need a heatsink on them. I don't understand why UA left it off.

Joe

 

[ibvee]

if it's below 30, it might not be the zener that's faulty though. To check the zener, desolder the wire connected to the top. Connect a resistor (in the order of 1k) to the top, and use a variable power supply (if it doesn't go above 30v, use a variable supply in series with a 9v battery). Measure the voltage directly over the zener, and turn the power supply voltage up. If the power supply goes beyond 30v (including the optional 9v) and the zener doesn't hold on 30v, it's faulty. Don't forget the resistor.