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Orange Crush 12 repair

Started by flester, March 26, 2018, 06:10:15 PM

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flester

Last yr my Orange failed and my local amp guy fixed it by replacing an Opamp chip soldered directly to the board. Now its gone again and I think I can fix it myself Is there any reason not to use an 8 pin socket instead for easy replacement of the chip? Theres only one 8 pin chip that I can see

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Jazz P Bass

Sure you can socket the ic.

First off, I would prove that the ic is bad.

flester

Quote from: Jazz P Bass on March 27, 2018, 01:01:03 AM
Sure you can socket the ic.

First off, I would prove that the ic is bad.
Yes that is the first step. If it is to be replaced, what are pros and cons to using a socket rather than soldering chip to board?

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flester

Quote from: flester on April 08, 2018, 07:20:18 AM
Quote from: Jazz P Bass on March 27, 2018, 01:01:03 AM
Sure you can socket the ic.

First off, I would prove that the ic is bad.
Yes that is the first step. If it is to be replaced, what are pros and cons to using a socket rather than soldering chip to board?

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Sorry I see you answered that already.
Any tips on how I would see if the ic is bad or not. Or should I seek professional help?

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tonyharker

You really need to find out why it is failing.  If you replace it odds are that it will fail again.. Op amps don't just fail for no reason!

Jazz P Bass

It was never stated exactly what is wrong with amp.

"Doesn't work" does not lead to the opamp.

flester

Quote from: Jazz P Bass on April 08, 2018, 11:54:59 AM
It was never stated exactly what is wrong with amp.

"Doesn't work" does not lead to the opamp.
Fair points. I think I will go back to the previous repair and not mess with it myself

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wetty

#7
If it failed once and it fails again following the same scheme:
A lot of ancient/recent FX/boutique amp designs use an unprotected TL072 or similar as input stage.
Often the poor input transistor gate is hard-tied to the phone tip without any protection. Suggestion: Insert a series resistor of 4k7 or 10k between Tip and OpAmp, connect two antiserial Zener diodes 2,7V from OpAmp input to GND.
From now on spikes or DC thumps from connecting DC ring-switched active basses/guitars are swallowed by resistor and zener. The gate junction stays alive a bit longer. And once somebody starts to unsolder an OpAmp: A socket is always handy.
One fine day you may want to swap a TL052 in. Or what ever crosses your mind...

flester

Had another look at this. The signal comes and goes when I move the Overdrive and or Gain knobs. I assume this could be an issue with pots or with whatever they are controlling? No schematic but I could almost draw one. See video here https://flic.kr/p/HX8P4L

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g1

I didn't have any luck with the video, but from the sound of your description, those pots might just need to be cleaned.

flester

Quote from: g1 on April 13, 2018, 02:10:03 PM
I didn't have any luck with the video, but from the sound of your description, those pots might just need to be cleaned.
Yes hopefully that might be all it needs. Surprising how simple the circuit seems by the way.  TDA2030 at the heart of ir. Should I be discharching caps before working on it or is that just for tube amps?

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solderer25

You dont need to worry about discharging caps as voltage across them not large enough to be a hazard in small SS amps. Just make sure amp is unplugged when you delve inside. To clean pots, get hold of some contact cleaner spray (Servisol or similar - not WD-40!) Fit the small tube (looks like a straw) into the nozzle and spray for a second or two inside the pots. There should be a small vent hole in the body of the pots into which you poke the tube and spray. Give the jack sockets a blast while you are at it. This is best done by inserting a jack plug to open the spring contacts before spraying. Good luck.

flester

Quote from: solderer25 on April 14, 2018, 02:51:59 PM
You dont need to worry about discharging caps as voltage across them not large enough to be a hazard in small SS amps. Just make sure amp is unplugged when you delve inside. To clean pots, get hold of some contact cleaner spray (Servisol or similar - not WD-40!) Fit the small tube (looks like a straw) into the nozzle and spray for a second or two inside the pots. There should be a small vent hole in the body of the pots into which you poke the tube and spray. Give the jack sockets a blast while you are at it. This is best done by inserting a jack plug to open the spring contacts before spraying. Good luck.
Overdrive pot needs replacement for sure. It is marked B250k but I believe B can be linear or log depending on market? All the pots (gain, overdrive, volume, low, mid, high) are B which guess means probably log?

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Jazz P Bass

If the control is marked 'B250K', then it is a linear 250K control.

flester

Quote from: wetty on April 11, 2018, 02:25:56 PM
If it failed once and it fails again following the same scheme:
A lot of ancient/recent FX/boutique amp designs use an unprotected TL072 or similar as input stage.
Often the poor input transistor gate is hard-tied to the phone tip without any protection. Suggestion: Insert a series resistor of 4k7 or 10k between Tip and OpAmp, connect two antiserial Zener diodes 2,7V from OpAmp input to GND.
From now on spikes or DC thumps from connecting DC ring-switched active basses/guitars are swallowed by resistor and zener. The gate junction stays alive a bit longer. And once somebody starts to unsolder an OpAmp: A socket is always handy.
One fine day you may want to swap a TL052 in. Or what ever crosses your mind...
I replaced the Overdrive plot and broke the pcb traces in the process. I then replaced the broken trace with a wire link (connected to R7 as  shown). When I ove the pot slightly I get either a weak output with a missing sound, or a loud bassy buzz, or a proper overdrive sound. All connections to the pot seem sound. Could there be an issue somewhere other than the pot?

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