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Author Topic: Twin Tube GFX-1  (Read 18138 times)

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bunkyloo

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Re: Twin Tube GFX-1
« Reply #105 on: Time Format »

Is there anything else worth trying on this thing? Any thoughts would be great.
Steve.
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MarshallJMP

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Re: Twin Tube GFX-1
« Reply #106 on: Time Format »

Well got too excited, as soon as I tested the unit powered up battery installed it read pin 1- 7.18 and 3-4.99 and then it crashed while testing so I tested battery in and 1 was5.15 and 3 was 3.642.
I then tested no battery and 1 was 5.54 and 3 was 4.04 and now won't boot with the 3.6 volt battery. :facepalm: .

The input voltage is too low, it needs to be at least 7.5V, with an absolute minimum of 7V. So 7.18 is already quite low, 5.15 won't work as you can see the output is only 3.64V, not nearly enough for all the 5V logic to work. Could be a few things, transformer, bridge rectifier BR2 or somethings is drawing too much current on the 5V line. Can you measure the AC voltage coming from the transformer? From what I can see it should be the 2 yellow wires on the connector next to BR1 and BR2. you should also be able to measure it on BR2 pin 3 and 4. BTW don't forget to put the meter on AC voltage!!
« Last Edit: Time Format by MarshallJMP »
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bunkyloo

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Re: Twin Tube GFX-1
« Reply #107 on: Time Format »

Ok across the the yellow wires unplugged I get 10.71 volts and plugged in I get 8.16 volts.
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MarshallJMP

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Re: Twin Tube GFX-1
« Reply #108 on: Time Format »

Ok that looks good to me, and you still have only 5.15V on the input of the 7805?
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bunkyloo

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Re: Twin Tube GFX-1
« Reply #109 on: Time Format »

Ok the 1 and 2 pins read 5.98 with battery out and 7.62 with battery in.
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MarshallJMP

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Re: Twin Tube GFX-1
« Reply #110 on: Time Format »

Strange that the voltage changes with the battery in or out?

Do you have have the old ic that you changed out?
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bunkyloo

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Re: Twin Tube GFX-1
« Reply #111 on: Time Format »

No I don't but i did buy an extra one I believe.
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MarshallJMP

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Re: Twin Tube GFX-1
« Reply #112 on: Time Format »

I checked the whole schematic and that ic is the only one where the 5V and the battery come togheter. So if you have a spare try to replace it.
Also before you put the new one in (and the old one is out) measure the voltages again. There is something very weird going on here.
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bunkyloo

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Re: Twin Tube GFX-1
« Reply #113 on: Time Format »

I swapped it out again and its the same old thing. This is really frustrating that we are running out of things to try.
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MarshallJMP

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Re: Twin Tube GFX-1
« Reply #114 on: Time Format »

Did you measure the voltages before you put the new one in?
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bunkyloo

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Re: Twin Tube GFX-1
« Reply #115 on: Time Format »

Well no I forgot to do that. :facepalm: I had been busy with work and when I had a moment I just did it.
« Last Edit: Time Format by bunkyloo »
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MarshallJMP

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Re: Twin Tube GFX-1
« Reply #116 on: Time Format »

Do you see any signs of modifications done to the unit?
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bunkyloo

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Re: Twin Tube GFX-1
« Reply #117 on: Time Format »

The only thing i see is the input and output pots have been replaced and wired to th board instead of pcb mount and they work fine but besides that no.
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MarshallJMP

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Re: Twin Tube GFX-1
« Reply #118 on: Time Format »

Ok the 1 and 2 pins read 5.98 with battery out and 7.62 with battery in.

I just can't figure out why the voltage rises when you put a battery in it.

Can you send (by email) a few high res pics of the inside of the unit? Maybe I can see something.
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bunkyloo

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Re: Twin Tube GFX-1
« Reply #119 on: Time Format »

Will do  this weekend . :bow:  :thumb-up:
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