Orange Tiny Terror Fault

Alex2678

I’ve recently picked up a tiny terror on the cheap with a view to fixing it, the issue is volume fluctuations and when playing clean there’s a very quiet distorted ghosting behind the note. Previous owner swapped all valves to no avail, I’m going to go through and check the solder joints etc and give it some contact cleaner but if anyone has any time saving pointers they’d be much appreciated!

ICBM

How old is it? That sounds potentially like it could be a filter cap.

Alex2678

Very, it’s a Korean one, so nearly 20 years? Thanks @ICBM , I’ll shall swap them out, changing them at this point won’t hurt either way 

Alex2678

Well, filter caps done, been through and checked for any iffy joints, contact cleaner in pots and jacks, and still got the issue. 

Sometimes it plays fine, then it’ll drop power with a distorted ghost note, then the signal was dipping in and out like a really slow trem. 

I shall continue digging 

ICBM

Alex2678 said:

Sometimes it plays fine, then it’ll drop power with a distorted ghost note, then the signal was dipping in and out like a really slow trem.

Did you do the power valve cathode cap as well? I wonder if that symptom is of the bias ramping up and down...

Alex2678

I didn’t,  it is the next thing on my list, but I tentatively think I may have fixed it. I found a couple of gnarly joints on one of the el84 sockets and it seems fine now. 

I’m not yet satisfied that it’s not going to come back as it’s been intermittent, but this is the longest it’s sounded ok for 

I had already looked over the joints in daylight but I went over again with my phone torch because it’s darker now and the heavier shadows revealed some weirdness 

ICBM

An EL84 making intermittent contact would do that, yes.

Alex2678

Probably something you’ve seen before ICBM but very odd looking couple of joints, they were very dull and domed with holes in. I reflowed them and as they cooled I could hear them crackle and the holes reappeared so i removed the old solder and redid them 

ICBM

Alex2678 said:

Probably something you’ve seen before ICBM but very odd looking couple of joints, they were very dull and domed with holes in. I reflowed them and as they cooled I could hear them crackle and the holes reappeared so i removed the old solder and redid them 

That can be caused by dirt on the component when you solder to it, which contaminates the solder. Cleaning it all off and renewing it is the right solution.

Alex2678

The issue has returned this morning, bypass cap next.
 
I’ve checked voltages at all the test points and valve pins and all seems fine

Alex2678

@ICBM not sure if this points to anything in particular- when the fault is present there’s a ‘whoosh’ as you turn it off or on, but there’s not when it’s working normally 

Alex2678

Definitely seems to be brought on by adjusting the gain control 

ICBM

It is very odd. At this point I would set it up on test with a sine wave signal and a scope and find out exactly where the distortion is occurring in the circuit.

Alex2678

Thanks mate I’ll see what I can do 

Alex2678

Just absolutely doused the gain pot in contact cleaner, don’t know if the construction of a dual gang pot makes it harder to get contact cleaner throughout but I can’t get it to show the fault again now. 

Odd symptoms but I think the gain control is an unusual design 

Alex2678

New gain pot installed, noticeably louder and clearer and so far no issues 

Keefy

I had one of these and had to replace the gain pot because it was cutting out. It was a bit of a pig to get the board out!

ICBM

That’s interesting - a duff pot doesn’t normally cause distortion, but I suspect you have found the fault if there’s been a noticeable change in the sound.

At least the other repairs were worthwhile too!

Alex2678

Yeah I’m not kicking myself over recapping/cleaning it. I only paid £83 for the amp as spares and repairs on eBay. 

It definitely didn’t sound like a duff pot, I was convinced it was the power supply or el84s, but the second gang of the gain pot is doing something unusual with the loading of the next stage 

Alex2678

Keefy said:

I had one of these and had to replace the gain pot because it was cutting out. It was a bit of a pig to get the board out!

The main thing that’s bugging me is how many screws you have to remove to get at the valves. 

And I’m not a fan of those push on connectors with the squeeze pins. I was fairly impressed with the quality of the pcb though, seemed to stand up to heat better than the one that was in my deluxe reverb 

ICBM

Alex2678 said:

The main thing that’s bugging me is how many screws you have to remove to get at the valves.

From memory it’s something daft like twelve to get at the valves, but only four to get at the much more dangerous inside of the chassis. Bad design.

The valve cover should be held on with four ‘thumbscrew’ type bolts, or if that doesn’t comply with safety regs now, four large-diameter screws that aren’t so easy to chew up or lose.