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Post subject: Help needed with ultimate chorus
Posted: Mon Apr 28, 2014 8:40 pm
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Hi everyone,
i'm a bit stuck on this one. a ultimate chorus came in to the shop with no output .my initial guess was the output transistors were bad. come to find out that i was right, kinda.
after replacing all 4 output transistors i'm getting sound, good sign right! well turns out the sound only lasts for about 30-60 sec. as i am running it through a limiter "light bulb type"
after a minuet i see somethings drawing way too much and the bulb is bright. i also went through and checked all of the diodes in the power section replaced 4 that were bad. to me it seems like it could be a bad cap since it takes up to a minuet for it to show any signs of failure. but after testing the caps on a capacitance meter and it saying there good im kinda stumped.

am i overlooking something ?

I just realized i titled it ultra chorus when actually it's an ultimate chorus, sorry


Last edited by t-rack7 on Tue Apr 29, 2014 9:34 am, edited 1 time in total.

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Post subject: Re: Help needed with ultra chorus
Posted: Tue Apr 29, 2014 1:38 am
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Any schematic ? I only have Ultimate Chorus schematic .

To have bad output transistor you need too much voltage on them or "short" load at output . What about load resistance ? Speaker short when hot ?

On Ult. Chorus I see diodes on each transistor Collector / emittor , check them if you have them .


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Post subject: Re: Help needed with ultimate chorus
Posted: Tue Apr 29, 2014 9:46 am
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i'll double check the diodes, i know i went through them before and replaced cr48,49
and also when i turn it on it works fine for a minuet and then the sound gets distorted. im having trouble uploading the schem. but it is a ultimate chorus. sorry for the confusion


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Post subject: Re: Help needed with ultimate chorus
Posted: Tue Apr 29, 2014 1:16 pm
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I talk about CR 38,39 for a side and CR 50,51 for other side . If they are short they destroy transistor . Those across collector / emittor.
What about Speakers ?

I wish you answer at my questions ,If not I can't help you .

I'm French speaking not easy to understand what you do .


What kind of bulb ? 100 watts ?

Did you try the amp ( power ON ) only with the 100 watts light bulb ?

Did you try the amp with no 100 watts bulb ?


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Post subject: Re: Help needed with ultimate chorus
Posted: Tue Apr 29, 2014 4:58 pm
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With it hooked up to the limiter what do you have on the output rails? I think you should unplug the amp and double check everything again. Did you replace all the output transistors ? If you do plug it back in I would leave it on the limiter until you know you got a solid amp. If its glowing bright that means its doing its job and something is wrong


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Post subject: Re: Help needed with ultimate chorus
Posted: Wed Apr 30, 2014 1:28 am
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goodinbed wrote:
If its glowing bright that means its doing its job and something is wrong



If it is a 100 watts bulb , I read some people use 60 or 40 watts


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Post subject: Re: Help needed with ultimate chorus
Posted: Wed Apr 30, 2014 4:50 am
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stratele52 wrote:
goodinbed wrote:
If its glowing bright that means its doing its job and something is wrong



If it is a 100 watts bulb , I read some people use 60 or 40 watts



Yes 100 watt bulb, and speaker is good


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Post subject: Re: Help needed with ultimate chorus
Posted: Wed Apr 30, 2014 4:57 am
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as far as the output rails i checked at CR 38,39 and CR 50,51 " running through the limiter "
it starts out at +30vdc, -30vdc then gradually starts to drop to around 8vdc and by then the two left side transistors Q8, Q9 are running hot so i shut it off.


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Post subject: Re: Help needed with ultimate chorus
Posted: Wed Apr 30, 2014 5:01 am
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goodinbed wrote:
Did you replace all the output transistors ?


Yes all four have been replaced


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Post subject: Re: Help needed with ultimate chorus
Posted: Wed Apr 30, 2014 5:16 am
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t-rack7 wrote:
as far as the output rails i checked at CR 38,39 and CR 50,51 " running through the limiter "
it starts out at +30vdc, -30vdc then gradually starts to drop to around 8vdc and by then the two left side transistors Q8, Q9 are running hot so i shut it off.



1- Transistor are not the good one

2- You mix/ invert NPN and PNP

3- Your new transistor (s) are defective, you overheat them when solder .


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Post subject: Re: Help needed with ultimate chorus
Posted: Wed Apr 30, 2014 8:51 am
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The 100watt bulb is fine and on ss amp you don't need a speaker hookup I would leave the speaker unplugged until you get the amp solid. You need to go back and check the your output section you still got something wrong and it's not panning out. I would go back and check your transistors and diodes are you using the meter on diode and to get a good reading pull one of the legs out on each part you test


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Post subject: Re: Help needed with ultimate chorus
Posted: Wed Apr 30, 2014 8:56 pm
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everything tested good on my atlas component tester. but i will check all transistors and diodes again with it and my meter


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Post subject: Re: Help needed with ultimate chorus
Posted: Thu May 01, 2014 2:31 am
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t-rack7 wrote:
everything tested good on my atlas component tester. but i will check all transistors and diodes again with it and my meter


It would be easy to me if you asnwer to all my all questions order .(post April 30 , 08:16 )

1- Old transistor number , new transistor number

2- Wrong transistor on wrong place ? You know what is NPN / PNP ?

3- You just answer to this one and you are nor sure if test is good......... :(


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Post subject: Re: Help needed with ultimate chorus
Posted: Thu May 01, 2014 6:25 am
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stratele52 wrote:
t-rack7 wrote:
everything tested good on my atlas component tester. but i will check all transistors and diodes again with it and my meter


It would be easy to me if you asnwer to all my all questions order .(post April 30 , 08:16 )

1- Old transistor number , new transistor number

2- Wrong transistor on wrong place ? You know what is NPN / PNP ?

3- You just answer to this one and you are nor sure if test is good......... :(



1. Q8,Q10 are TIP142 Q9,Q11 are TIP147
2. transistors are in the correct position, i know NPN/PNP
3. All Tested Good
I Hope that makes sense


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Post subject: Re: Help needed with ultimate chorus
Posted: Thu May 01, 2014 6:43 am
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t-rack7 wrote:
stratele52 wrote:
t-rack7 wrote:
everything tested good on my atlas component tester. but i will check all transistors and diodes again with it and my meter


It would be easy to me if you asnwer to all my all questions order .(post April 30 , 08:16 )

1- Old transistor number , new transistor number

2- Wrong transistor on wrong place ? You know what is NPN / PNP ?

3- You just answer to this one and you are nor sure if test is good......... :(



1. Q8,Q10 are TIP142 Q9,Q11 are TIP147
2. transistors are in the correct position, i know NPN/PNP
3. All Tested Good
I Hope that makes sense


Thank's for answers

Now what it is the problem ?

100 watts light bulb starting glow low and after 30- 60 second come very bright ?
You got sound first 30- 60 second and after you loose sound ?


I'm right ?


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