Mc7150 shorted swapping bulbs, won't turn o

[McFixIt]

I was swapping bulbs on an mc7150, flipped it on to test the bulb i had just done, the bulb tails crossed and shorted. Fuse on the back is still good. Won't turn on... how bad did I screw this up??? Any ideas where to start looking?

 

[clinic-audio]

Hello
What bulb are you talking about ? Meter bulbs ? Front panel bulbs ?
What do you mean by "test bulb" ?
Swapping bulbs ? If your bulb do not light on , replace it ! but swapping them why ?

 

[seabee1]

it might have seemed like a good idea at the time

 

[McFixIt]

I had 2 bulbs for the face that were burnt out, so I was replacing all of them. I was on my 4th out of 5, i was completing each solder then switch the unit on to test the connection & bulb before moving to the next or reassembling parts. Should I have finished and then put things back togather and then tested?? Sure. However thats not what happened. In the morning I will put some media through it to see if its the face or the whole unit thats out. Im assuming there is a fuse somewhere for the face electronics... I figure someone on here knows whats under the hood on these things

 

[clinic-audio]

I had 2 bulbs for the face that were burnt out, so I was replacing all of them. Good idea and much better if you replace them all in once

I was on my 4th out of 5, i was completing each solder then switch the unit on to test the connection & bulb before moving to the next or reassembling parts. not a good idea at all

Should I have finished and then put things back togather and then tested ?? Sure. However thats not what happened. In the morning I will put some media through it to see if its the face or the whole unit thats out. Im assuming there is a fuse somewhere for the face electronics..

Of course if you made a short somewhere that everything stay in the dark ! what lamps did you used ? Original type ?

Now you know why a qualified tech is necessary to do this job ! now I will be curious to see how you will check what is wrong ....

I am pretty sure that you don't have the service manual

If it is not your job , I will strongly recommend you "don't touch anything if you don't have the service manual "

There is one fuse for the light and it is slow low 1,5A

 

[McFixIt]

I do have the service manual. The 1.5A fuse on the meter pcb is still good so I will get into the service manual and probably start chasing things from there back to the power supply i should find the issue. If I didn't feel I was up to the task... or would be devastated if I bricked it I wouldn't be working on it... but I do have a near compulsion towards messing with stuff.

 

[clinic-audio]

Good news if you have the service manual !

How many voltage (AC Volt) accross each lamp ?

Since over 40 years in many many unit the voltage line is a pair of brown wires (coming direct from the power transformer ) and they are there only for lamp circuit
These wires can't give you zero volt , so check starting these wires why your amplifier stay dark

 

[McFixIt]

Thanks for the 2 brown wire tip!! I got 10v across the browns... 120 at the power switch. Checked continuity on the fuse on the meter pcb, seems like a bad fuse there. I checked it visually last night and it looked good. Still looks to be in fine shape but not getting continuity. I'm assuming this is my issue. I have ordered replacements. I will report back when those arrive. I'll finish swapping and solering bulbs in the mean time. I have removed the power gaurd pcb and connected back lights, i need to sort out a way to power this and bench test it independant of the unit. The two bulbs that were out (why I am replacing bulbs with LED) are burnt down to the board and in real rough shape. I may have to see if audioclasics had a replacent pcb.

Do you think without the this fuse and without the power gaurd pcb the amp would not even play? I am getting no sound when I try it.

 

[McFixIt]

So Christmas is over and I had time get back into this. Problem solved, LED panel bulbs soldered in (some of those were burnt out) I left the meter bulbs as they were still good but have LED and filters for later. Turned out to be the fuse on the meter pcb. It showed continuity several times when I tested it in place. After removing and testing showed no continuity. I rigged the wrong size but right amps fuse in to test, new fuses are on the way.

LEDs look great. Does not show hot spots, green is a little more vibrant. I dig it.

 

[McFixIt]

I think this deserves an update. I have extensively blind ab tested this amp... I balanced the volume db level across all 3 amps and ran spotify through a heos connect across 3 zones through marantz sr7008 and paradigm studio 20 v5, for reference. first against a marantz mm7025 and second vs 2x emotina upa 1s and mcintoshmc7150, in blind ab tests the mcintosh won. It is a subtle difference between all 3. The mc is across the board smoother, bolder and more authoritative then any of the other 2 pairings (sorry I don't know how to better describe it). Dont get me wrong, the marantz mm7025 is great, the emo upa1 are awsome. I would happily own any of them from here on out ( probably will keep both). THE MCINTOSH IS BETTER. Is it 3x+ price better?? Not in a million years. Buy the mm7025 or the upa1. I will attest to the fact you get 90% of the performance for 20% the price. If you
want blue meters... no one will fault you, not the least your self. A 30 year old mc is a cut above today's midfi for sure. Bottom of the line the mc beats both... all are good, you can't go wrong even with an efficient speaker.

I found a good deal on revel f36s and the matching center. Will audition on Saturday and look forward to testing the mc 7150 with these in my main set up vs the emotiva upa1s.

 

[audiobliss]

Smoother, bolder, more authoritative! !
That's exactly how I was trying to describe my new found MC7270 compared to my MC152.