Help Requested- T-Rex Replica V1 - Broken - One faint repeat.

byrne347

Hi there pedal people. 

I have a V1 Replica (the one with the small "subdivision" and "Brown" buttons). The pedal will turn on but will only faintly let through one repeat, no matter what you do with the repeat or echo time. The Level pot works fine as does the tempo (both the pot and the footswitch change the tempo perfectly. 

 On the Echo potentiometer as you turn up past 12 o’clock the output level gets quieter. Which is strange. 

 I have measured each potentiometer and they read good on a multi meter. I have also reseated the ribbon cable connecting the two internal PCB boards and checked all the solder joints and wires for bad connections, which there do not appear to be any

 I assume one of the components dealing with the echo repeats has gone bad but I’m not an engineer and don’t really know how to test it much more than I have.

Like an idiot I thought I would buy a second broken one on ebay and use the two to make one working pedal, but the second one has exactly the same fault and now I have two broken Replica pedals. Yes, I am aware I am an idiot/ double-down clown.

I emailed T-Rex and they are willing to fix it but for more than the pedal is worth + shipping to Denmark. They also said they could not diagnose the issue from the description I sent them, but it does sound to me like this is a common issue so I would think they could give me some advice. 

It may be as simple as a replacement ribbon cable or someone putting in the wrong power which fried one component I can replace. 

Anyone have any experience with this pedal and what may be the issue? 

Tips on someone in the UK who may be able to fix it for a decent price? 

Any assistance would be very much appreciated. 

Andy

Danny1969

Often, if the level of something decreases when turning the level up it's because the level pot is controlling the amount of negative feedback of an opamp, or an IC with an opamp stage on the output. What often happens is either the opamp dies or it's power rail dies ... but the negative feedback from output back to input provides a path around the chip to the output

However when the chip works a higher resistance in the negative feedback path = more gain. 
But, if the chip or it's power supply dies the pot varying the negative feedback amount will have the opposite effect. Increasing the level of it = less gain and a quieter output

I'm not familiar with this pedal or it's circuit but when fault finding any device with IC's, after checking for obvious faults  start by making sure each chip has Vcc,  ground and enable pin activated (either high or low depending on the chip) 

To get a pin out of a chip google the chips part number and add pin out. 

stylesforfree

As far as I know the components for the replica V1 are now obsolete, how much did T-Rex quote you for the repair?

 As Danny said above, in regards to the volume issue it definitely sounds like an opamp gone bad.

If you're just getting one faint repeat it's very possible that there's a faulty capacitor that might have dried up, so I would start with recapping it maybe?

Also I know you bought a 2nd one to try and fix the first one....but there's 2 on reverb now for relatively cheap.

These guys have a load of 5 star reviews: Guitar Amplifier Repair, Newark, Nottingham UK - Keld Ampworks

Sorry im not much help!

byrne347

@Danny1969 ;

@stylesforfree ;

Thank you both for your responses.

T-Rex quoted me circa £80 (for each). I know it isnt bad but if its one op amp I feel a bit silly sending it to Denmark and back for something I could potentially replace for under £5. I also have had some bad experiences in the past convincing UK customs that the package that is coming back to me after repair from the EU is actually something I already own. (ha) 

I tested a lot of the components on the board as per Danny's tips and compared them to the data sheets values I get the correct values across all the ones tested so far though the 'Hex inverting Schmitt trigger' (whatever that is) it seems to have some odd values, but again, this is out of my wheelhouse. 

What is handy is having two here is I can compare each components vcc against the other. I appreciate the inherent danger in that with two broken pedals that seem to have the same issue, but I have to start somewhere. 

Maybe T-rex will take pity on me and do me a deal on two repairs and then I can sell one on one repaired to recoup some losses. 

Thanks again to you both for your response. I will keep trying my piecemeal repairs. 

Andy