Mark IIC+ very ill! Please help!

[Massimo]

Hello everyone,
I'm Massimo from Italy and I just joined the forum because I own a Mesa Boogie MkIIC+
but I know next to nothing in electronics and I really need some good advice
I want to thank you all in advance in case you want to take some time to help find a cure for my amp

My beloved amp served me good for many year with no problems
Then for the last almost 10 years is been sitting in my rehearsal room unused (I've turned it on sometimes, but not often)
Last summer I went to turn it on after a long time with some apprehension that after such a long time
being unused it could get damaged upon being fed current again
To my great relief the amp turned on normally and worked fine as usual
I've used it for a few days and then left it alone for the last 3 months
Yesterday I went to turn it on again and the silence I heard froze my blood!
Upon switching it on the power led lit, but there was no hum from the amp (I mean the normal hum you hear when turning an amp on)
Lookin at the back I could see pre and power tubes getting to normal glow
After the initial dismay I took out the chassis ( I'm aware of the high voltage danger) and put it on a table just hoping to spot
an internal fuse that I could have replaced (that's about all I know of electronics!...)
Another thing I know how to do is replacing the V1 pre tube which is said to be the main cause of many problems and so I did
with no result except for more dismay
Now, since the tubes are glowing normally, I suppose that the Power Transformer is be ok. Is that right?
But hearing no hum makes me suspect that maybe the Output Transformer is damaged
Could this happen just by turning the amp on?
Can you help me find out what the problem could be?
Is there anything I could do before taking the amp to a local tech?
Thanks a lot
Massimo
ps: I shot a short video of turning the amp on and watching the tubes glow and I'll post it if required. Thanks
ps: Hope my english is good enough to be understood

 

[b00g13mk2B]

Check that the speaker is plugged in and is good. Being on (power and standby) with no speaker load can cause damage.

You can try a known good guitar cord in the effects loop. Sometime the send and return jacks can get oxidized and cause an open circuit for the signal path.

There are other measurements you can make, but with the tubes glowing normally I wouldn’t worry about measurements. Others can chime in. Old manuals have basic troubleshooting tips, none needing test equipment.

 

[Massimo]

Thanks for your prompt reply, b00g13mk2B
Sorry I didn't mention that I did the Send/Return test
The speaker Is well connected and I went throu the troubleshooting in the amp manual and none seems to fit my case.
My concern Is that I don't hear the tipical noise of the amp being switched on
Note: In case some measurement is needed, I know how to use a tester. I just need a guide to find the spots where to take the measurement. Thanks

 

[FedWar]

Thanks for your prompt reply, b00g13mk2B
Sorry I didn't mention that I did the Send/Return test
The speaker Is well connected and I went throu the troubleshooting in the amp manual and none seems to fit my case.
My concern Is that I don't hear the tipical noise of the amp being switched on
Note: In case some measurement is needed, I know how to use a tester. I just need a guide to find the spots where to take the measurement. Thanks

Ciao,
just call Massimo Mantovani at M-tech audio and speak with him on the phone, I had most of my mesa (including IIC+) serviced by him.
If the amp has never been recapped, this might be the perfect time to do this as well.
I would not recommend to poke around with an amp that has an high resell value, you might cause more damage.
which model is it by the way?

 

[Massimo]

Ciao,
just call Massimo Mantovani at M-tech audio and speak with him on the phone, I had most of my mesa (including IIC+) serviced by him.
If the amp has never been recapped, this might be the perfect time to do this as well.
I would not recommend to poke around with an amp that has an high resell value, you might cause more damage.
which model is it by the way?

Ciao FedWar,
thanks for the advice although I've never heard of M-tech
I could call him but he'd want to see the amp and I'm 350 Km away from Modena
He's running a business and I'd understand if he wouldn't be wasting his time on the phone with me
How did you meet him? Do/did you live in Italy?
Just because is a valuable amp I would like to get a clue of what happpened to it before bringing it to a local tech, so (just in case) not to have it messed up with
I mostly would like to know: can be that the OT get damaged with long inactivity?
Or at the first switch on after long inactivity?
Thanks

 

[FedWar]

Ciao FedWar,
thanks for the advice although I've never heard of M-tech
I could call him but he'd want to see the amp and I'm 350 Km away from Modena
He's running a business and I'd understand if he wouldn't be wasting his time on the phone with me
How did you meet him? Do/did you live in Italy?
Just because is a valuable amp I would like to get a clue of what happpened to it before bringing it to a local tech, so (just in case) not to have it messed up with
I mostly would like to know: can be that the OT get damaged with long inactivity?
Or at the first switch on after long inactivity?
Thanks

Ciao Io sì vivo in Italia. A mio parere è uno tra i migliori tecnici che abbiamo in Italia punto ha praticamente revisionato modificato o tutta la mia collezione di amplificatori. Secondo me è in grado di aiutarti anche telefonicamente. Poi sarà lui a consigliarti che prove fare per capire dov'è il danno. PS anche io vivo più di 350 km e glielo ho sempre mandati senza problemi. Basta impacchettarli bene tipo con pluriball polistirolo e doppia scatola mai avuto un problema in tutti questi anni.

 

[steve Rhenius01]

Ciao,
just call Massimo Mantovani at M-tech audio and speak with him on the phone, I had most of my mesa (including IIC+) serviced by him.
If the amp has never been recapped, this might be the perfect time to do this as well.
I would not recommend to poke around with an amp that has an high resell value, you might cause more damage.
which model is it by the way?

I‘d Chechen the speaker and leads to it - use a low voltage battery 9V to make sure it pops. After that check the AC mains input to the rectifier then dc high voltage on the capacitor board then at the anodes of each valve. Boogie transformers are pretty strong so failure is unlikely unless it’s a bad connection. Other than that you need the advice of a tech - ask at studios or even local amateur radio club (Joe Walsh was a keen radio amateur !). Be especially careful working around high voltage AC and DC. Good luck, Ciao.

 

[Henz]

After CAREFULLY doing what Steve suggested, Btw, not to step on Steve's toes, the anodes he's referring to are pin 3 of the power tubes. Be careful there as well because amp has to be fully powered up. There should be about 480vdv +/-, though being an export, not sure. .there are other very basic tests one can do with just a digital voltmeter. One is with amp UNPLUGGED and filter caps discharged, though the two 150k bleeder resistors do a good job, check for voltages on filter caps. The large cylinder shaped components on power board and one on preamp board. Once UNPLUGGED,
, check the plate resistors on the preamp board. Two on each. Pins one and six. Check to see if any are open and / or are within tolerance. Always probe with one hand! If not confident with above, take to a tech. Keep us updated. One more thing, not only check for a failed V1 tube, test others as well. Do this first.

 

[Massimo]

which model is it by the way?

Sorry, forgot to answer...what do you mean with which model?
Isn't MKIIC+ the model? Are there more details to it?

 

[Massimo]

Hi, thanks to all for your contribution

It is with some embarassment that I must admit that I left the speaker (2x12 ext cab) test for last, so sure I was that it was working fine
So after having replaced all the pre tubes one by one and even the power tubes and having thought to test that there was signal from the Slave and the Send outputs, which it was, I did , just for the sake of it, plug the amp into another cabinet and guess what?
the amp seems to be working just fine! I said "seems" because I still can't believe it and I'll have to turn it on again and again to convince myself
I wouldn't have been able to do the tests with the multimeter you suggested anyway so the amp would have
gone straight to a tech with all that it envolves....including being laughed at!
Now I must see what's going on with the cabinet, but that's an easy task
Thanks so much for your time and support
Maybe let's wait a few days before closing this thread, please, just in case...

 

[electric mayhem]

Much easier to fix a cab!
Congratulations and enjoy.

A word of caution on the OT's:
Always always always keep a speaker plugged in; one that is working

Short blasts aren't going to kill the OT but just like a 2ohm load on a 8ohm tap is a dangerous mismatch, no speaker has no load to keep the OT in check and therefore much much worse-it won't take very long to blow a non-replaceable shcumacher with no load.

 

[FedWar]

Sorry, forgot to answer...what do you mean with which model?
Isn't MKIIC+ the model? Are there more details to it?

Of course there are.
60w, 100w or 75w (simulclass)?
Graphic eq or not?
Export power transformer or US domestic

 

[Massimo]

Of course there are.
60w, 100w or 75w (simulclass)?
Graphic eq or not?
Export power transformer or US domestic

Oh, ok...
Mine is a 100/60W (don't know if it is Simulclass, whatever that means ) with a Graphic EQ and must be US domestic since I bought in LA back in 1993 and its running on 115V
And it's the walnut cab model
Fell in love with the amp when I first saw it
It was Keith Richards playing it in the Hail Hail R'n'R concert
So I just grabbed it when I found one for sale in the Recycler ads

 

[FedWar]

Oh, ok...
Mine is a 100/60W (don't know if it is Simulclass, whatever that means ) with a Graphic EQ and must be US domestic since I bought in LA back in 1993 and its running on 115V
And it's the walnut cab model
Fell in love with the amp when I first saw it
It was Keith Richards playing it in the Hail Hail R'n'R concert
So I just grabbed it when I found one for sale in the Recycler ads

Nice!
100w/60w is class a/b only and hence it is not simulcass. (Class a/b and class a in parallel).
If you ever want to sell, let me know!
Ciao

 

[Massimo]

Much easier to fix a cab!
Congratulations and enjoy.

A word of caution on the OT's:
Always always always keep a speaker plugged in; one that is working

Short blasts aren't going to kill the OT but just like a 2ohm load on a 8ohm tap is a dangerous mismatch, no speaker has no load to keep the OT in check and therefore much much worse-it won't take very long to blow a non-replaceable shcumacher with no load.

Thanks, electric mayhem!
Yeah, that's one of the few thing I know: always keep a load in amp output and I never turn my amps on without a speaker connected, and just in case, I always have the amp volume turned down when I switch it on
I'm so glad this turned out to be just a speaker problem!

 

[Massimo]

Nice!
100w/60w is class a/b only and hence it is not simulcass. (Class a/b and class a in parallel).
If you ever want to sell, let me know!
Ciao

Thanks for the info!...
Selling it? This amp will follow me to my grave!
Ciao

 

[steve Rhenius01]

Hi, thanks to all for your contribution

It is with some embarassment that I must admit that I left the speaker (2x12 ext cab) test for last, so sure I was that it was working fine
So after having replaced all the pre tubes one by one and even the power tubes and having thought to test that there was signal from the Slave and the Send outputs, which it was, I did , just for the sake of it, plug the amp into another cabinet and guess what?
the amp seems to be working just fine! I said "seems" because I still can't believe it and I'll have to turn it on again and again to convince myself
I wouldn't have been able to do the tests with the multimeter you suggested anyway so the amp would have
gone straight to a tech with all that it envolves....including being laughed at!
Now I must see what's going on with the cabinet, but that's an easy task
Thanks so much for your time and support
Maybe let's wait a few days before closing this thread, please, just in case...

A learning curve. We’ve all made these mistakes , hopefully only once along the way. Great that it seems a simple fix.

 

[Massimo]

A learning curve. We’ve all made these mistakes , hopefully only once along the way. Great that it seems a simple fix.

It seems to be a faulty speaker jack...it even works now but I will replace it
Speakers ( 2 Vintage 30s) read well on the multimeter
Thanks, you all, for your support and...patience!