EZ1073 Build

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FelixT

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May 6, 2021
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Hi all, I realise there are a couple of threads on this unit but I was unable to find my solution there. If anyone could help I'd be hugely appreciative!

Background for context of my experience - built a lot of pedal kits, built an AB763 style valve amplifier from Rob Robinette's plans, lots of soldering experience but less experience of schematics, however I know much more now than before I built the amplifier.

I get no relay clicks when powering on my EZ1073 and the voltage between TP1 and TP2 is the full 16VDC from pin 12. I get signal through the unit but is very crunchy and thin. The gain adjust trim pot works, though I haven't found a way to test the bias adjust pot in the circuit (though I have tested the pot is varying resistance correctly).

When putting together I was very meticulous and checked front and back of PCBs for soldering quality on each component. I've also checked over the schematic to see if I can work out why this is happening but I don't have the mental capacity to understand what's causing the issue. I have also gone over every joint checking it is good, and removed most of the flux on the back side of the main board.

Something else to note but I'm sure is nothing - the kit came with only 1 x 1N4007 when it should have had 4. Luckily I had a load and so I replaced them from my stock, untested. Could they be part of the problem?

I'd love some schooling on what could be the problem and how to understand how those test points can show me the bias (which must be for the 7808, right??!).

Here is the PDF, schematic on page 39 - http://www.audiomaintenance.com/downloads/ez1073pre_colourbook.pdf

Thanks in advance anyone that can help!
 

ruffrecords

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Nov 10, 2006
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13,417
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Norfolk - UK
If you have no relay clicks then you need to check the surge control assembly. Make sure you have fitted the right resistor values and that C49 and D9 are the right way round.

Cheers

ian
 

FelixT

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Joined
May 6, 2021
Messages
16
Location
London
Hi Ian, thanks for your reply.

I've checked those over again now;
tested values of all resistors on the surge board - all correct.
checked orientation of diode (D5, there isn't a D9 that I can see on the build..?) - correct.
checked orientation of polarised cap C49 - correct.

I've checked for a visual short around that board but seen nothing. Could it be that D5 has been burnt out on installation? I know diodes are a bit sensitive to heat, so didn't cook it too badly (I thought).
 

StevieG

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Jul 25, 2016
Messages
6
I built the free standing version of this kit and found it relatively easy to signal trace audio through it. You’ve probably checked this but bear in mind that a low level and trebly output can be the result of connecting a transformer balanced output to an unbalanced input, but forgetting to earth the negative side of the transformer? I was caught out by that one!
 

FelixT

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May 6, 2021
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London
Thought I’d finally add some photos - a few before I take it apart and go over all of the joints.

the molex connector for the output tx I could never get all the way down - perhaps this is part of the problem?

i added flying leads to the bias test points as otherwise it was impossible to test when in my lunchbox

also the rear of the board on the last pic shows an example of the joints
 

FelixT

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May 6, 2021
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London
Can anyone see anything like I’ve got the input tx the wrong way around or something silly like that?
 

FelixT

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May 6, 2021
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Location
London
are D3 and D4 in the right direction?
I’ve just double checked and yea they’re in the right way around. Could I have fried them during install? I’ve got a load of 1N4007s so could just replace to be sure..?
 

FelixT

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Just to triple check
 

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FelixT

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May 6, 2021
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London
Yeah I double checked D5 too. When I get a spare moment I’ll go over everything again checking resistors etc. I think the relay not clicking is the big clue to what the issue is. Does that mean that the relay is seeing the wrong current or no current at all?
 

fragletrollet

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Sep 19, 2010
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Oslo
I've built 4 of the line versions, and the only problem I had was on the first one, where I mistakenly swapped the longer and shorter screws that fasten the output tx, resulting in the pcb being at an angle to the back plate and front panel. This resulted in the fingers on the pcb edge not properly mating, and the unit wouldn't power up. Switched the screws and all was good.

Not saying its the same, but sounds like your unit isn't getting power, or atleast the relay. Worth checking!
 

noiro

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Joined
Oct 22, 2011
Messages
18
did you fix it, when you power it up do you hear the relay clicking, take a few seconds, then listen if you hear a second click then you have an issue, perhaps a short
 

FelixT

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May 6, 2021
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Location
London
Hey noiro, I haven’t yet had a chance to get to the bottom of this, busy with clients (thank god!) but when I’ve had it in the rack it’s not switched the relay at all.
 
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