Request for help: DSL100 power instability on power-up

[michibarchen]

Hi Everyone,

I have a DSL100 head that struggles with power instability on power-up. I plan to take the amp to get serviced by a professional, but I'd be glad to hear your take on what may be going wrong. I'm intrigued by the problem, and I hope you may be too. Thanks in advance.

Some background:
I bought the amp new in 2006 with a manufacture date of the same year. I played it modestly for three years, and then stopped. The amp then lay dormant from ~2010 to 2020. It took on no physical damage during that time, and neither was it subjected to the elements or temperature extremes. No mods were done during that time, and neither did it receive any servicing. It just lay dormant. I started playing it again in 2020. It powered up just fine (though I did not use a variac as perhaps I should have), worked like new, and sounded great for several months. It continues to do so, except for one problem.

The problem:
On power-up, the amp does not immediately turn on. I can count up to ~30-35 seconds before the pilot light comes on, the channel indicator light follows, the tubes light up, etc. Once every few power-ups, though not always, the amp will subsequently shut off at random within the first ~30 seconds of power-up, several seconds will then transpire, and then the amp will power on again. Sometimes this repeats, while sometimes it does not. But when the amp appears to have enough juice, it runs just fine. After that, all is well with the amp (as far as I can tell). The amp never again struggles with power while in use.

My insight:
I am no pro, but my instinct suggests the filter caps are to blame. Or, at the very least, something in the power-up section seems off. I can confirm that the voltage from the wall is as it should be, the power cord is not damaged, and the fuses are not blown. Nothing inside the amp appears burned or blown, and the amp works like a charm once the power-up stabilizes.

Any suggestions or insights of your own? Many thanks for your help.

-Michael

 

[Gunner64]

First, I would be suspect of the power switch itself, and its spade connectors, the power cord jack on the back, the mains fuse holder, and the spade connectors on the power trans and any other main power contact point as possible points of loss of contact issues that would cause intermittent loss of power.

 

[IOSEPHVS]

Some capacitors, e.g. electrolytic, degrade over time. This can be exacerbated by non-use. I'm not sure, but it might have to do with the filter capacitors for the rectifier circuit.

 

[Gunner64]

Some capacitors, e.g. electrolytic, degrade over time. This can be exacerbated by non-use. I'm not sure, but it might have to do with the filter capacitors for the rectifier circuit.

The op said the pilot light, as well as all power to heaters, and channel indicators are lost when it happens. If it were the rectifier for the b+ just the sound would go, not the intire power to the amp.

 

[Max Gahne]

If I have the correct amp, your pilot light is in the rocker switch and all that is before even the power transformer. Unplug it and look for corrosion and connections in the fuse holder in the power cord socket and then look at the rocker switch itself. Before you turn it on sometime and it's nice and cold UNPLUG it and turn the rocker switch on and with a meter see what resistance you have across the switch on both leads. Should be about zero. With it UNPLUGGED resistance from your power transformer mains leads to the wall plug should be about zero with the switch on. The schematic I'm looking at for what I think you have shows an arcolectric switch with a neon bulb. Neon, old neon often takes awhile to come on. Shouldn't have anything to do with the rest of the amp powering up. But makes me go hmmmm.

 

[Gunner64]

If I have the correct amp, your pilot light is in the rocker switch and all that is before even the power transformer. Unplug it and look for corrosion and connections in the fuse holder in the power cord socket and then look at the rocker switch itself. Before you turn it on sometime and it's nice and cold UNPLUG it and turn the rocker switch on and with a meter see what resistance you have across the switch on both leads. Should be about zero. With it unplugged resistance from your power transformer mains leads to the wall plug should be about zero with the switch on. The schematic I'm looking at for what I think you have shows an arcolectric switch with a neon bulb. Neon, old neon often takes awhile to come on. Shouldn't have anything to do with the rest of the amp powering up. But makes me go hmmmm.

Exactly what I suspect. Post 2. Somewhere in the mains power coming into the amp, not just the neon.

The op said he was taking it to a tech, and wasn't going to look at it himself, but just wanted a basic idea what may be wrong. With the symptoms he describes I think we're pretty close. No heaters, no channel indicators, no pilot lamp. It has to be a main power issue, as none are connected any other way.

 

[Max Gahne]

I understand it's not just the neon. We're on the same page Gunner64. But neon is wierd to me, can neon cause corrosion? Does the little neon lamp have a ballast? If this were a game show I'm saying it's the switch. And yes michibarchen if you're not experienced troubleshooting electronics take it to a tech.

 

[Gunner64]

I think I'd be chopsticking the spade connectors, pushing the rocker switch a bit in a wiggle type manner, and pushing on the mains fuse holder trying to replicate the problem. That's what I'd do. Other than the power transformer itself it has to be one of them.

 

[michibarchen]

Hi Everyone,

Thank you all for your insights and suggestions! It is very nice to get such excellent feedback and support from you.

I think you're all spot on too. I have one additional observation to offer, and I wonder if it supports your reasoning:

If I were to use the amp for a while, then shut it off, and then turn it back on after only a few minutes, the amp powers right back up with no intermittent power loss. Could that be due to something that remains conductive at or near where there is a loose/corroded connection in the power-up section (if that is the case)? I ask because, as you have correctly assessed, the amp struggles to turn on from a cold start.

Many thanks once more.

 

[Gunner64]

I do know things expand with heat, that may be part of the intermittent nature of your issue.

 

[michibarchen]

Good to know. Thanks again for your help!