So about that SPEC-4...

[mikebw]

I decided to close up the case and test it out while I wait for the new binding posts to arrive. I plugged in some speakers turned it on and it was great! For about 30 seconds. It just stopped working.

I was playing with my source volume and it was quite loud & clear through my test speakers, but about 30 seconds into the song the sound just cut off. The lights on receiver stayed on, meters stopped moving, so I turned it off. hmm.

I tested all the components I was using on a separate amp and they're working fine so the problem is isolated to the SPEC-4. I'm letting it sit unplugged overnight to see if it comes back in the morning, but at this point I am officially bummed.

Could this be a defective cap issue? Any other ideas? No burned smells or anything suspicious to my eye. I do have a local repair shop that I trust to work on this but I would like to figure it out myself (with some help of course).

Thanks. Hopefully you guys aren't getting tired of me yet.

[jtaylor]

> I decided to close up the case and test it
> out while I wait for the new binding posts
> to arrive. I plugged in some speakers turned
> it on and it was great! For about 30
> seconds. It just stopped working.

> I was playing with my source volume and it
> was quite loud & clear through my test
> speakers, but about 30 seconds into the song
> the sound just cut off. The lights on
> receiver stayed on, meters stopped moving,
> so I turned it off. hmm.

> I tested all the components I was using on a
> separate amp and they're working fine so the
> problem is isolated to the SPEC-4. I'm
> letting it sit unplugged overnight to see if
> it comes back in the morning, but at this
> point I am officially bummed.

> Could this be a defective cap issue? Any
> other ideas? No burned smells or anything
> suspicious to my eye. I do have a local
> repair shop that I trust to work on this but
> I would like to figure it out myself (with
> some help of course).

> Thanks. Hopefully you guys aren't getting
> tired of me yet.

Are the FUSES still good???????

[mikebw]

> Are the FUSES still good???????

Checked the main fuse and it's fine, after all, the lights still come on. I am not aware of any other fuses on the unit- are there more? Where would I look?

[AJ]

This doesn't sound like a completely catastrophic failure, so with some good troubleshooting you should be able to get it working reliably again.

Does the unit have a relay based protection circuit? Like do you hear a click when you power the unit up? If it does, check the relay contacts.

I would probably pull the circuit boards out and clean them well, then look around for cracked solder joints, loose wiring etc... Just take a double close look at everything. Inspecting solder joints with a magnifying glass can reveal cracks easier. Caps that look deformed, or leaking need to be replaced. I would consider replacing the small electrolytic caps on the board just because of the units age. The big power supply caps are probably okay, as these big old can caps seem to hold up well.

This doesn't sound like a completely catastrophic failure, so with some good troubleshooting you should be able to get it working reliably again.

If you either find issues or not, power the unit up and put a multimeter across the output terminals. Set the meter to read dc voltage and see how much dc offset the amp has. Anything below 100mv is marginal, and below 30-40mv is perfect. Check both channels and let us know what you come up with.

I wouldn't suggest power the amp up again until you've taken a very close look at the circuit boards.

Good luck, and be safe.

[jtaylor]

> Checked the main fuse and it's fine, after
> all, the lights still come on. I am not
> aware of any other fuses on the unit- are
> there more? Where would I look?

WOW, I forgot that amp was basically two amps in one cabinet as how its been described. It sounds like you need a Schematic for this rascal about now, you may be able to find one on Google. Usually they put fuses on each rail of the power supply. Do you have a DMM meter for checking voltage, Caps, or Coils?

If the main fuse plugs into the amp in the back somewhere, there may be other fuses mounted on circuit boards for the rail power that powers the amp power transistor sections.

I hate to say that my experience is with Phase Linear 400's, so I can't provide that much help except for a few basic things, sorry.

One other thing when checking an amp of that vintage. Use just a cheap single speaker for testing as line voltage or high DC voltage could be on the outputs, which destroys speakers rather fast. I'm sure you don't want to chance destroying good speakers for testing. I wish I could provide more help, at least you don't have much reason to feel guilty anymore.

J. Taylor

Bad Caps are a prime possibility for its age.

[AJ]

I just took a closer look at the photos you posted below.

The relays are those two black boxes in between the filter caps. I see they have a 120vac rating so that means they probably cut the power to the transformers in case of a fault, or they are just for a soft-start circuit. If they are for a protection circuit, i would think they cut the power to the unit altogether. Meaning the lights would shut off.

There could be fuses for the power lines coming from the power supply to the circuit boards, and there could be fuses on the speaker outputs somewhere. If any of these fuses are blown you have a problem elsewhere. You need to troubleshoot and find the problem. DON'T just replace fuses.

A picture of the circuitry underneath would be useful.

[philiparcario]

Provided Link: spec 4 manual


> I decided to close up the case and test it
> out while I wait for the new binding posts
> to arrive. I plugged in some speakers turned
> it on and it was great! For about 30
> seconds. It just stopped working.

> I was playing with my source volume and it
> was quite loud & clear through my test
> speakers, but about 30 seconds into the song
> the sound just cut off. The lights on
> receiver stayed on, meters stopped moving,
> so I turned it off. hmm.

> I tested all the components I was using on a
> separate amp and they're working fine so the
> problem is isolated to the SPEC-4. I'm
> letting it sit unplugged overnight to see if
> it comes back in the morning, but at this
> point I am officially bummed.

> Could this be a defective cap issue? Any
> other ideas? No burned smells or anything
> suspicious to my eye. I do have a local
> repair shop that I trust to work on this but
> I would like to figure it out myself (with
> some help of course).

> Thanks. Hopefully you guys aren't getting
> tired of me yet.
Here is a link. I purchased from them last year. 2 manuals came fast in good shape.

[cjb]

...but if nothing else - buy the service manual! The only thing that brings more money on Ebay for a dead amp is a service manual and good pics. Oh, and it sounds like it might be a problem in the transistor department. But I'm no expert. My brother is the amp guy; I'm just stickin' my nose in. -CJB (I'll see if I can get his opinin and get back with you)

[mikebw]

> If you either find issues or not, power the
> unit up and put a multimeter across the
> output terminals. Set the meter to read dc
> voltage and see how much dc offset the amp
> has. Anything below 100mv is marginal, and
> below 30-40mv is perfect. Check both
> channels and let us know what you come up
> with.

I turned it on with nothing connected, gain knobs set to zero and then put the leads from my digital multimeter onto the speaker outputs, set to mV.

Left channel read .2mV, Right channel .3mV. That's pretty darn good no? Or could that be anomalous? Of course the amp is still not working... I don't know what the readings were before. Seems like if some protection had triggered the offset would be irrelevant right now.

[AJ]

> Seems like if some protection
> had triggered the offset would be irrelevant
> right now.

Yup.