HEADROOM Headphone Amp repair help :)

[JazKazman]

My vintage desktop Headroom 'Home' amp has stopped working and I was wondering if anyone here could either recommend someone who could service it for me or better yet suggest a DIY option? Here's a couple of pics and a description of the problem just in case you could offer some advice to a novice as to how to proceed. Thanks for having a look...

1- No sound comes through at all after powering it up - although the red power light does come on and I can hear the headphones connect with an audible electronic click/static when plugging them in.

2- I've attached a photo of the interior to see if I could easily spot the culprit but no luck. Maybe it's obvious to professionals?

3- I've tried both inputs sources on the back (there are two and all the gain switches etc. but nothing is coming through - just "dead air".

Wondering what the problem may be -- if I'm to troubleshoot it myself (being a novice who does own a multimeter at least - lol) or send it...somewhere?


I'd love to have it working again as I had so many wonderful listening years spent with it. Any help or suggestions would be much appreciated.


Many thanks.


Cheers!

 

[MaxwellsEq]

Did you get any warning of the fault? Has it been taking longer to start up or have three been crackles, drop outs or shutdowns (e.g. when hot)?

Did both channels die at the same time? If so, you are looking for something common such as a PSU rail failing, or Dual op-amp.

Unless something burned out in a dramatic fashion, or there is an obvious dry joint, visual inspections are often not much help for diagnosis.

To fix things, a circuit diagram is often essential, especially one that shows expected DC conditions. Ideally you need a signal generator (these days a DAC will do) and something to measure DC and AC signals, preferably up to high frequencies. An AC multimeter with good high frequency behaviour can work. An oscilloscope is often helpful.

 

[JazKazman]

Thanks for your comments. My son was the last one to use it (a few years back now) and he did say that he heard a 'loud pop' and then...no sound (on either channel).
Does that mean a capacitor blew? I don't see any bulging or obvious damage to any components. If it was that would have to de-solder each one of of them to test. I have very limited experience in that but would be willing to try it. I do have a DAC (who doesn't these days ;-) so could try that step. As to getting a schematic I'll try but unfortunately there's not too much online about this earlier model Headroom.

 

[Doodski]

Is there a fuse anywhere? Those 2 Ohms resisters near the power supply look prime for measuring the positive and negative voltages in reference to ground. To see if the power supply is outputting voltage. Alternatively check the primary of the transformer for a open thermal fuse. There should be near a dead short at the primary.

 

[JazKazman]

Thanks. I'll have to decipher the basics first (being a total newbie ;-) re: the components to check. I don't see a regular fuse anywhere. The deck does power up though- just no sound so it would be nice if it was just a fuse. I'll try poking around as you suggest. Cheers!

 

[JazKazman]

Okay I just googled 'thermal fuse' ( I'm a real newbie ;-) and now understand what I'm to check for. It did say that they only react to excessive temperature, not excessive current so when a loud pop was heard before it died I'm assuming it was due to a power surge or something.

 

[Doodski]

Okay I just googled 'thermal fuse' ( I'm a real newbie ;-) and now understand what I'm to check for. It did say that they only react to excessive temperature, not excessive current so when a loud pop was heard before it died I'm assuming it was due to a power surge or something.

The thermal fuse will be in the transformer primary inductor if there is a thermal fuse used there. If there is one and it is open then some electronics surgery will be required to access it and jumper it for test purposes only.

At the power supply transformer primary inductor use the multimeter on the lowest resistance setting it has and look for very low resistance like in the single digits. If the multimeter has like hundreds or more Ohms indicated then there is something bad. We will cross that bridge when we get there.

 

[restorer-john]

There should be near a dead short at the primary.

Not in a 15VA transformer. It'll be above 900R for a 120V primary.

The thermal fuse will be in the transformer primary inductor if there is a thermal fuse used there. If there is one and it is open then some electronics surgery will be required to access it and jumper it for test purposes only.

This is silly advice, Doodski. There's no need to check the primary, letalone dangerously suggest he dig into the windings looking for a thermal fuse. Because he's already said this: "although the red power light does come on and I can hear the headphones connect with an audible electronic click/static when plugging them in."

and he said this: The deck does power up though

Step one should be checking all your rails. There's clearly 4 separate regulators maybe more on the back of the PCB- who knows.

If the OP wants to post better shots of the upper and lower sides of the unit, he has a DMM, steady hands and can follow simple instructions, I will endeavour to help. Otherwise he should leave it well alone, get a professional to look at it or throw it out.

 

[JazKazman]

Thanks all. I will get some better pics up in the next day or so. Although a newbie I don't mind trying a few new things in my old age (lol). I do tinker with some vintage wind-up watches that don't run and actually get some working again so the thrill of getting this amp working again will be worth the lessons. Much appreciated btw. I have a few digital multimeters (and an analog one or two)... and soldering tools etc. Failing that I'll send it off to a pro. p.s. I'll check the back of the pcb board as suggested and include pics. cheers!

 

[solderdude]

It can't be a thermal fuse as the LED indicator still works so there is at least some DC voltage present at the output of the rectifier.

The fact that both channels cut out indicates maybe the + or - supply voltage may not be present.
These appear to be coming from separate windings and have the same regulators which are then tied together after the regulator so a +/- 15V supply is created from 2 'separate' regulated 15V regulators.
Most likely something happened in either one of the regulators (parts on the right side) or the small PCB which is the amplifier part.
One channel on the upper side, one channel on the bottom side.

I don't think it is a capacitor. Seems like something electronic that affects both channels.

 

[JazKazman]

Sorry for the delay. Attaching a few better photos now. In one I put an arrow where I spotted something that may be causing the problem - but I am not sure. I did clean it up a bit (with alcohol) but didn't want to reassemble the board into the case and try it until I had your input. I am ready to now try your suggestions as to how to proceed. Many thanks

 

[JazKazman]

I took quite a few photos so could zoom in on any spot and upload close-ups if requested. Cheers!

 

[JazKazman]

..and one more question ;-) These are my three old DMM's. Which would be best for this task?

 

[middlemarch]

Just noticed this. I'm astonished at the amount of flux on the smaller PWB. It's as if no effort was made to wash the board after assembly? Before doing any troubleshooting it may be worth while to remove that assembly and thoroughly clean it in a batch of 91% isopropyl alcohol. There should be no flux visible and the PWB should be as clean as the main PWB. The charring on the leads of one of the devices indicates it got hot, so that may be an indication of a problem, but get that board clean first. There's a reason PWBs are (should be) thoroughly cleaned after soldering.

 

[JazKazman]

Thanks. I was wondering why it appeared so 'dirty' and thought to clean it with alcohol without removing it as I really have no experience with that. Is it relatively easy to remove for a total newbie willing to give it a go?

 

[JazKazman]

I do have an ultrasonic cleaner btw that I use for my vintage watches. Would that be another step that could help clean that board? cheers

 

[middlemarch]

I would just give it a go with iso and a brush. Best if you can remove it, no telling what's on the other side. Be careful to pull straight out so you don't bend the pins. I hope you realize this is for fun, as in an educational experience. I'd just buy an Atom+ for a hundred bucks and call it a day...

 

[JazKazman]

Would I have to de-solder all of these 'solder feet' to remove it and if so is it difficult to re-solder them back? Or would it be better to slice them off at the center of each each with a dremal tool?

 

[JazKazman]

Yes I know it's all just for fun as otherwise it goes in the trash...but hey, I'm a stubborn old guy who hates throwing anything away. My son has an Atom amp after killing my old Headroom (which sounded great to me way back when --lol)

 

[JazKazman]

I'll try cleaning it with a brush first as you suggest.