• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

MC 2100 power issue

M

MattB238

New Member
Hello, im new here and new to the electronics realm of vintage audio, but have a fairly decent understanding of how it works. My issue: I have recently recapped my Mac MC 2100 (minus the multi section can), cleaned and deoxed, and made a dim bulb tester. It was my understanding the amp requires 75 watts at zero output and went with a 150 watt bulb for the tester. At the moment of truth, I plugged her in and ZERO dimming whatsoever. Not a quick dim back to bright or anything for that matter. From there I used a 75 watt bulb, with the same results. My question is, if there was absolutely no dimming of the bulb, am I correct in assuming the issue is "close" and not deep within the unit, or is that just showing my lack of understanding? And, any suggestions on what to do next? Thanks.
-Matt, KS, USA.
 
Register to hide this ad
MattB238 said:
Hello, im new here and new to the electronics realm of vintage audio, but have a fairly decent understanding of how it works. My issue: I have recently recapped my Mac MC 2100 (minus the multi section can), cleaned and deoxed, and made a dim bulb tester. It was my understanding the amp requires 75 watts at zero output and went with a 150 watt bulb for the tester. At the moment of truth, I plugged her in and ZERO dimming whatsoever. Not a quick dim back to bright or anything for that matter. From there I used a 75 watt bulb, with the same results. My question is, if there was absolutely no dimming of the bulb, am I correct in assuming the issue is "close" and not deep within the unit, or is that just showing my lack of understanding? And, any suggestions on what to do next? Thanks.
-Matt, KS, USA.
Click to expand...
You need to look up how a Dim Bulb Tester (current limiting) works.
From you post it looks like you are not grasping the basic concept of the DBT.
 
kevzep said:
You need to look up how a Dim Bulb Tester (current limiting) works.
From you post it looks like you are not grasping the basic concept of the DBT.
Click to expand...
Well I think I do, at least I know the bulb should dim to almost nothing IF all is well with the gear you're testing, meaning most if not all the current is going to the amp in this case, right? What am I missing?
 
MattB238 said:
View attachment 2340741
Click to expand...
A diagram might be better.....The lamp should be wired in series with the AC Mains supply.

Maybe I read it wrong but it sounded to me like you were expecting the lamp to be fully lit? You said you had "zero dimming" which implied that you expected the lamp to be fully lit and when the amp was on it would dim?
Thats the way I read it.

Is the amp actually working?
 
kevzep said:
A diagram might be better.....The lamp should be wired in series with the AC Mains supply.

Maybe I read it wrong but it sounded to me like you were expecting the lamp to be fully lit? You said you had "zero dimming" which implied that you expected the lamp to be fully lit and when the amp was on it would dim?
Thats the way I read it.

Is the amp actually working?
Click to expand...
Gotcha! No. When I said no dimming I meant the bulb did NOT dim. It stayed fully bright. Yes my DMT is in series.
 
I think that with an MC2100 if you are not seeing the bulb dim, especially the 150W bulb, something is wrong in the unit. You should not draw a ton of current (i.e. your bulb should be dim, barely lit filament) when on the DBT w/ no signal in/out.
 
MattB238 said:
Gotcha! No. When I said no dimming I meant the bulb did NOT dim. It stayed fully bright. Yes my DMT is in series.
Click to expand...
Oh right, yes you have a problem!!
I am in the Southern Hemisphere, that must make me see things backwards because we are upside down!!

What is the history of the amplifier? Was it working, or have you just got it and you want to diagnose it, or you've done some work to it?

Bright Bulb is showing there is a dead short in the amplifier somewhere, so could be a number of things, most commonly blown output transistors, sentry monitor transistors, drivers, could even be one of the main caps shorted......the list goes on.....
 
As stated above, the bulb should not be full-bright. I rebuilt my 2105 using either a 40W or 60W, not sure I remember, 150W is definitely overkill.

What is the voltage measured across your bulb?

What should happen, with the 2100 "cold", capacitors discharged (not plugged in for lets say 30minutes or more) is you plug it in to your DBT, lets go with a 40W, when you switch on the power to your 2100 the bulb glows brightly as the power supply capacitors charge, over about 2 seconds it dims to what I'll call half-brightness, and the 2100 starts playing music happily.

If OTOH you get to the turn-on point, the bulb glows brightly, 2, 3, 4, 5 seconds later the bulb is still glowing brightly, it is indicating that the 2100 is drawing enough current to act as a short-circuit. Fortunately the low-wattage bulb is limiting the voltage into the 2100, and the current to the 40W bulb's .3A current draw (circuit in series) which shouldn't do any damage to the the amplifier if there's a short-circuit.
 
Last edited:
SaturationPt said:
As stated above, the bulb should not be full-bright. I rebuilt my 2105 using either a 40W or 60W, not sure I remember, 150W is definitely overkill.

What is the voltage measured across your bulb?

What should happen, with the 2100 "cold", capacitors discharged (not plugged in for lets say 30minutes or more) is you plug it in to your DBT, lets go with a 40W, when you switch on the power to your 2100 the bulb glows brightly as the power supply capacitors charge, over about 2 seconds it dims to what I'll call half-brightness, and the 2100 starts playing music happily.

If OTOH you get to the turn-on point, the bulb glows brightly, 2, 3, 4, 5 seconds later the bulb is still glowing brightly, it is indicating that the 2100 is drawing enough current to act as a short-circuit. Fortunately the low-wattage bulb is limiting the voltage into the 2100, and the current to the 40W bulb's .3A current draw (circuit in series) which shouldn't do any damage to the the amplifier if there's a short-circuit.
Click to expand...
 
MattB238 said:
Would the results change if I went with a lower watt bulb?
Click to expand...
Clearly the MC2100 has a fault, so I would be working on that rather than worrying about what wattage lamp I should be using in a current limiter. Use a 100 watt lamp so you're not limiting it too much, but giving the amp enough protection, next, get on and work through the amplifier to asses the damage and build a parts list.....
 
Searing75 said:
Curious as to why you chose not to replace the multicap as well?
Click to expand...
Not sure really. I want to keep it as original looking as I can I guess and the process of "re-using" the outer can and stuffing it with new eltrolytics seemed daunting to me. I just for the life of cant see why replacing a few elctrolytics in the amp, including the 2 big filter caps, would cause a short somewhere. I only messed with boards that needed caps replaced, and nothing more. The unit was working just fine prior to this. Guess thats what I get for trying to learn as I go.
 
If this is your first rodeo or maybe even your second, I'm guessing you have one of the large caps connected backwards.
On the Positive supply the Negative terminal connects to ground.
On the Negative supply, the Positive terminal connects to ground.

Check this out, take a picture and post your work so we may be able to spot the error, but I think there is a good chance this is what you've done, I have seen this so many times with guys who are learning.
 
I'm with @kevzep on checking the caps, would be the first thing I check also.

Regarding the wattage? I know because I rebuilt my 2105, that a 60W will give a healthy 2105 (2100 draws even less) enough supply voltage and current to operate "normally" enough to hear music and test the unit. It will allow roughly half as much current to flow, so even more sensitive components will survive if there's a fault/short, therefore I start small. My DBT allows me to throw switches to add more bulbs or bypass completely after I pass the initial startup, so it's easy for me to say start small, ... The 2100/2105 is a simple power supply, no inrush protection relay with voltage/current sensing, so the 40W will work fine.

Regarding what will be different with a smaller (wattage) bulb (other than less current)? The bulb might glow brighter, but you're already indicating a short so no need to re-test until you've found and corrected your short. It will glow brighter for a little longer when the unit is working properly because it takes a few seconds longer to charge the PS caps, but again if it stays bright for more than a few seconds it's a short.
 
Man, I truly expected a bunch of critizism when I posted this, but it's been nothing but helpful info! Thank you. Let's see, the large caps. Im almost positive they are correct, due to me replacing them as soon as I took the old ones out one at a time. If the painted dots on the caps themselves are an indicator a person has them installed correctly, then I have both dots showing through the chasis. Am I correct in that?
 
You must log in or register to reply here.
Back
Top Bottom