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I've been looking for a small cheap practice amp for the last few weeks, and I settled on a vox pathfinder 15r. On ebay these things go anywhere from $140-170 functioning, so i figured i'd see if i could get a good deal on a damaged one and try to repair it.
I did end up buying one for way less and it's being shipped now. It would be fulfilling as a man to repair an amp and use it, but after doing some more research it seems like you have to know what you're doing to not get electrocuted with a solid state.
"The tremolo depth and reverb knobs do not have a start/stop point (defective). The reverb does not work at all and may be an internal breakage of the pot itself. Also the amp will play well but then will cut out for short amounts of time and then come back in full volume."
This is the description of the damage. The fact that the amp actually makes noise seems like a good sign to me. I saved enough money on buying a damaged one that if it really gets tough i could just take it to a repairman, but i'd rather not.
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06-16-2015 05:16 PM
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Unless it is a very valuable SS amp, often it's not even cost effective to have a tech do a bench test.
Yes sir, your $100 amp needs a $75 repair, that'll be $60 for the diagnosis please.....
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Yeah.. sorry.. I might take a look at that but if the pots are busted getting the right replacements might be a pain.. amp cuts out could be just a crack in the circuit board.. if it were my amp I would take a crack at it since I have been doing this for a while, otherwise probably not worth it to fix.
I could be wrong but your best bet is to find someone who thinks they can fix it and hope they give you a good price for it.
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As far as safety goes, if i look up standard electric precautions and look at diagnostics or something, I could be able to figure it out?
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To fix an amp, you need documentation, tools, electronics knowledge, and a methodical approach - otherwise you're in trouble.
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Replacement parts are often hard to find, too.
Originally Posted by Engine Swap
Danny W.
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Based on this question I would say no. Fixing a solid state amp could be extremely simple or near impossible. If it truly is just broken pots, you could do it but you need a regulated soldering iron and a good solder sucker because they are almost certainly board mounted. Originally Posted by prsguitar
- Is the amp through hole or SMT?
- Do you have lots of experience working on PCBs and not lifting traces?
- Do you have access to the schematics?
- Do you have experience reading & sourcing the right parts for electronics?
Amps can contain lots of components, and in modern SS amps, they can be really tiny. If it is SMT you need specialized tools to get the parts off and on the board. For all intents and purposes SMT boards are usually just replaced entirely.
Looking at a Vox Pathfinder it looks like it is through hole—at least some of it—with fairly big traces, so it could be doable if you have the tools.
vox.jpg Photo by jasonsoutthere | Photobucket
If it didn't cost you much, and you want to get into electronics, experiment away—just make sure if it has big filter caps, you discharge them. If you want an amp to use for playing music, take it to a tech—they may discover other issues that could crop up later.
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OTOH, I started out tinkering with amps with no experience. Got shocked, blew stuff up, had some success. I went on to get a degree in electronics, which led to a career in aerospace, eventually the audio business.
Be safe and learn as much as you can. Tons if info and help online.
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I see heartache in the OPs future if he continues down this path.
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There's a lot of voltage in a Solid State amp and some big caps, which retain voltage even after you turn the amp off.
If "live", work with only one hand, so the voltage won't pass between both hands and stop your heart.
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I was quite pleased when I managed to repair the reverb in my Fender Twin. It just stopped working one day, so I opened the reverb tank and had a look. There was a tiny broken wire carrying the signal from the spring unit to the outer contacts, and do I mean tiny, didn't look much thicker than a human hair! It must be so easy for that wire to break.
So I replaced it with a more robust piece of wire and soldered it in. Has worked like a dream ever since.
But really that was just a simple soldering job with no sensitive components nearby (the reverb tank is completely separate from everything else, and detaches from the floor of the cabinet).
I wouldn't trust my limited soldering skills anywhere near a printed circuit board!
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One of the easiest ways to waste money is to try to save money. The law of diminishing returns is always in effect as you ascend the echelon of cost, but with that in mind and a little common sense, "you get what you pay for" is a pretty darn stable theory of thought and practice.
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Originally Posted by whiskey02
Genius. Unbeknownst to me, that was my manifesto for many years.
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I saved about $120 buying it broken. So i have a lot of room for error in my quest to fix it.
In other news, does anyone want a broken Vox pathfinder 15r?
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With all due respect and best wishes for you prsguitar, until it's functioning properly as you would wish it to be, you haven't saved anything just yet. I'm not against "bargains", I just don't know that you've got one yet. Hope it all works out for you.
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Here is a link to get the schematic
Guitar Amplifier Schematics and more
There are clues here. The pots aren't mounted on the board but they both need replacing.
The volume drop may be caused by a crack in the board as mentioned above or it could be a cold solder joint.
The highest voltage east of the pwr tranny is 31vDC. The voltages in a tube amp can be north of 350vDC.
So unless you touch a electrolytic cap you should be ok.
Do some research in:
Draining pwr caps.
Soldering.
Reading Schematic diagrams.
Be sensible and good luck.Last edited by ColMc; 06-18-2015 at 03:57 AM. Reason: Don't know east from west.
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Sounds like a decent flea market or yard sale buy at $5. Disconnect the amp leads from the speaker and, if you already have a head, you've now got what might be a decent 8" cab.
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Aside from the danger / skill level issue ... do you have a temperature controlled soldering iron? A good Weller is about $90.
Weller WES51 Analog Soldering Station - Soldering Irons - Amazon.com
That cuts into your savings but if you plan to do any modding / soldering in the future, it is absolutely worth not cheaping out on. I bought mine 10+ years ago and it's one of the best purchases I've made.
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Alright so I just got it delivered today and played it for a few minutes. The volume skipping out is only apparent within the 10 seconds after I turned on the amp, but it didn't skip once afterwards. The tremelo works, but can only turn from 7 to 2 o'clock before it just keeps turning and doesn't affect the sound of the amp. The reverb does not work at all, and in one picture you can see the knob doesn't fully attach to the amp (I don't know the technical words yet). Everything else is functional.
Sorry the pictures are sideways.
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Now take the back off and more pics please.
Also, most important, unplug the cable from the wall socket while
you're working on it. Not just switched off but unplugged.
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I've gotten this far, it looks like everything i need to look at is on the other side of the circuit board, but it's covered by the metal plate. Should i separate the circuit board from everything else? oh and now the pictures are upside down. Great.
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the tremelo and reverb are the only things that don't work. I never use tremelo, and i'm sure I can find a reverb petal or get a good sound from my multi effects petal if it really comes down to it. I want to fix this but it seems hard, clearly.
http://music-electronics-forum.com/a..._schematic.jpg
There are 4 wires that seem to come from the reverb springs that end up on the circuit board at W3 and W4. And the reverb knob is ground at VR47. I can only get this much without taking the metal plate holding everything together. Just watched a video on how to seperate circuit board from everything else, didn't realize it was held together by the knobs.
Ok, newest update. I opened it up, and in the pictures, the nearest pot is the reverb one that isn't working. It doesn't looking visually different from the rest, but the "screw" just sticks out further than the rest, which is why the knob wasn't as close to amp as the rest of the knobs.Last edited by prsguitar; 06-18-2015 at 11:14 PM.
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Your model is not the same as the schematic I found and it looks like, as you say the pots are board mounted.
If you're not so worried about the reverb and tremolo at this stage, the only problem is the cutting out.
Do some research on 'cold solders joints'.
And can you post a close up of the circuit board showing the solder joints near the left side.Last edited by ColMc; 06-18-2015 at 11:29 PM.
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check for darkened spot on the circuit board. That usually indicate the component is burned.
I hope you have the right tools to unsolder the pot.
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I think i found the problem yesterday. The reason the knob sticks out is because the pot that is on the reverb is THE WRONG POT. it's simply the wrong one. Maybe the original pot was broken before and someone tried to fix it and bought the wrong one, put it on without realizing it was wrong, then sold it. Anyways I ordered the right one, along with soldering gear, and i'll try to fix it when everything comes in.
Last edited by prsguitar; 06-20-2015 at 08:30 PM.
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