Mesa Boogie Single Recto V2 Burned Resistor(s) Help !

[moshpit903]

Actually I am mainly ordering the tube sockets to have on hand if I have to drop the amp off at a tech,might save some time and $$ if they say that my amp needs new tube socket(s)..I haven't seen any arcing anywhere,this board actually looks great minus the small area of the burned resistor,but I have only gone over the traces and checked for continuity and its all checked out,but I am writing all of what you are saying to check and will get on it tomorrow morning..
I do know this and thats these parts are way to close to each other,I payed attention and got a good solder job done,and I lifted the resistors up off the pcb,and the pcb isn't as flimsy as the Jet City i worked on.
Also the original post from way back the OP was instructed to take everything out from around the V1 area and go to town on it,but looking at mine,and having 2 other people inspect it its fine.
What really bothers me about this whole Mesa amp thing is I've been wanting a Mesa Rectifier amp for quite a while now and was pumped up and happy to have a good backup for my EVH 5150-3 amp head,and had an opportunity to make an even trade I was truly happy and then the big let down,but this amps pcb has 2000 as the year made so its been around,and the guy i traded with said he owned it for 2 years and didn't have any problems with it so I guess it was time for it to malfunction.with all that said I believe its fixable for sure and the cosmetic condition is good with the original in good condition aluminum Diamond plate face plate I polished to the max and a few small tears in the Tolex,but none of that matters really,I just need to quit BS'ing and figure it out.
I knew as soon as I saw Enzo as a Moderator that this forum has some excellent knowledgeable people,he helped me on the another forum early last year and the repairs were a success and the amp was awesome !
I will check back in probably tomorrow evening after another busy day..Thanks again !

[moshpit903]

Instead of guessing whether it's 39 ohm or 39k ohm or whatever, please find out where it is in the circuit and we can look at the schematic and see what it is. Take a meter, set it to low ohms scale or diode check or continuity beep and measure from the traces where the resistor goes to each pin of the preamp tubes and find out what pin and what tube it goes to. If you put in the wrong value resistor, you could do more damage or the amp won't work right. There's no need to guess. Also, I have to ask,...... why are you changing tube sockets? Is there evidence of arcing or something we don't know about?

Real quick here,now when doing these checks do I have the power tubes,preamp tubes in or out of the amp,all or none etc..? I do know to always have a load/speaker hooked up and the amp will be on and the Standby will be in the amp on position,full power..

[doombass]

Real quick here,now when doing these checks do I have the power tubes,preamp tubes in or out of the amp,all or none etc..? I do know to always have a load/speaker hooked up and the amp will be on and the Standby will be in the amp on position,full power..

When doing continuity checks like the ones The Dude asks for you will do that without tubes and no power on at all. We're not measuring voltages yet. Do you have a meter to use for this? If not, you'll need one, because there's no way to properly diagnose anything without it.

[moshpit903]

When doing continuity checks like the ones The Dude asks for you will do that without tubes and no power on at all. We're not measuring voltages yet. Do you have a meter to use for this? If not, you'll need one, because there's no way to properly diagnose anything without it.

Yes I do have 2 great digital multi meters that work great..1 auto ranging and the other normal. You are right,I should have known that about no power on,thats to determine voltage.
I am going to go ahead and take my time and do it right,as in slightly grinding the remnants of the burned spot under the 1 bad resistor and epoxying it up with the green conformal coating,or if any other way to do it cheaper and other type of epoxys, or wait it out until i order it online and wait-2-5 days to get it ? I did see a quality repair job on one of these same amps on the 2015 original forum members thread and he said his amp worked and sounded awesome,and thats what I want ! Time to try to sleep now and start on this tomorrow.

[doombass]

Yes, a good night's sleep is always welcomed. Cleaning things is good, but you will still need to track down where that resistor go in the circuit. Otherwise it will still be guessing as to what made it burn out.

[Pedro Vecino]

39 Ohms resistors (39.2) must be those above. They are part of the heaters line in the first tube (even the second one although it does not appear in the schematic) and the switching circuit (+ 3 / -3V).
Measure in the first socket between pin 9 and pin 4 to see if they are approximately 5.8VDC.

The resistor, although blackened, may have good value. Desoldering a pin can be measured without problem.

The problematic part associated with these circuits is usually the group of four diodes. Sometimes they leave a blackened trail on the PCB due to overheating even making it conductive.

I´ve never seen a useless socket in Rectifiers. It is very unlikely that this will happen. If anything, it might require mechanical tension to the pins.

[Randall]

"so this 39.2k resistor is a 5 band resistor that is from top to bottom..Orange,,white,,red..Black..Brown..according to the 10 5 band resistor charts I looked at thats 39.2.."

Nope. 392 x 1 = 392 ohms, 1%. And 1/2 watt is pretty much assumed if it isn't indicated otherwise.

I don't mean to be unkind here, but based on just this, maybe you don't have the skills or basic understanding needed to be working on a potentially lethal tube amp.

[moshpit903]

"so this 39.2k resistor is a 5 band resistor that is from top to bottom..Orange,,white,,red..Black..Brown..according to the 10 5 band resistor charts I looked at thats 39.2.."

Nope. 392 x 1 = 392 ohms, 1%. And 1/2 watt is pretty much assumed if it isn't indicated otherwise.

I don't mean to be unkind here, but based on just this, maybe you don't have the skills or basic understanding needed to be working on a potentially lethal tube amp.

Well whatever the case is today the Mesa tech emailed me back again and said "on the Solo 50 parts list I see four 39.2 ohm resistors and one 39k resistor.. so I'm going with a 39 ohm 1/2 watt 1% in metal film resistor,or a 39 ohm 1/2 watt 5% carbon film resistor..why the 5% ? Because I have looked and one of the guys at Mouser electric told me thats what he could in carbon film..no 1%er's..
I will finish this job out in however long it takes me,if I get over my head I will take to a tech because I don't and won't wait forever to play through this amp.

[g1]

You mentioned it is blowing mains fuses. If you are determined to continue with the repair, you should look up and build the 'light bulb limiter' so you can find the cause of the fuse blowing.

[moshpit903]

Well, if you have it torn down already, no need to reassemble it. Just follow the trace or use a meter to see which tube pin the resistor goes to. Check from the traces where the resistor was to tube pins until you find continuity.

Hey I did this just now and on V1 tube socket pins and the trace where the bad resistor was I don't have continuity at pins 1 & 6..the rest of them have continuity..I meant to check it when I had it put back together but came in and took chassis apart and remembered..so I did this what you have said.
I'm going to call it the night for anymore work on the amp and off here but if you have more stuff you can recommend I am all ears..
I did order some of that Green conformal coating so I can scrapes this burned part off the pcb and fill up with this,and hopefully go to next step towards one day being able to actually play through the amplifier. Thanks for the good info.

[nevetslab]

Two things. First, I have never seen a 39.2 K resistor, and 1% is pretty unusual.

I used to know this 96 step value sequence without having to stop and look up a number for the nearest 1% value, but.....392 is a standard 1% value in the sequence. Here's the sequence, just for fun.

STANDARD 1% Res VALUES.pdf

Those two 39.2 ohm resistors by pins 4 & 5 in the photo.....they're across the +/- 3VDC filament supply shown in the power supplies schematic Jazz provided. I thought The Dude was correct in the 39k resistor being the only '39' value in the schematics, being cathode resistor for V2b

[moshpit903]

My conformal coating I ordered had a delivery date on Monday,and it didn't get here,and the USPS promised delivery date is today the 19th so i am still waiting on the mail to come.
I did scrape and gouge out all the carbon on the board,which really was just under the burned resistor and a small dot sized on the other side of pcb.
All my tracers look really good and have continuity throughout the whole pcb,or where they all go so I guess ok for now..just waiting on USPS.

[moshpit903]

My conformal coating came in finally this morning,and I mixed up a small batch and filled in the area(s) where I scraped/gouged out the carbon on the pcb..after it fully cures I will go back over it with all the info I have been given above and see what I come up with..I do like how this Circuit Works cw2500 sets up..already curing nicely.
I will still probably take it to the tech but I can't help but think that after I check it all out again if I should solder in the 2 new resistors and fire it up..I guess it will depend on my mood at that time but even if I take it to the tech I figure maybe 2 hours tops to fix it up,so maybe $90 would be worth it.

[moshpit903]

Ok,now as I wait on this amp I have been doing some reading on the replacement of the 2 large Blue 220uf-300vdc and 1-30uf-500vdc electrolytic caps and have seen many opinions,but one stuck with me saying that "the industry standard of time to replace these caps is 20 years".

I have also read a lot about the caps being dented,leaking,and if the amp was used a lot or not used much it can dry out the caps or wear out the caps..
This amp shows 2000 Mesa/Boogie so I am thinking and had had verified from MB that this is a year 2000 amp..now I don't know the whole history of this amp but looking at the caps they all look great with a visual inspection,but that might not be enough info to not go ahead and change them out myself and maybe keep this amp from more harm..this amp when I had it on and using it it seemed very quiet at idle.. any ideas,thoughts on when to change the caps ?

[moshpit903]

Update on amps status..about 11 days ago I drove to an amp tech about 60+ miles from my house and took my amp to him after speaking to him 3 times over the telephone prior to going to their shop,when I took the amps chassis in the "Tech" I spoke to all of a sudden had this awful look on his face and started telling me it was going to be really expensive to work on and repair my amp,so I asked him to call me with a cost amount before beginning work,so I left amp with him but on my way home I thought about what he said and how awful he looked at me,so I went back and got my amp an hour later and the guy actually "Thanked Me" for taking my Mesa away..
So bummed out on wasting $20 in gas and 4 hours drive time I decided to make 1 last call to a small repair shop that I used 1 time before and the lady I spoke to gave me a telephone # to another shop,I called and the guy said YES I repair Mesa amps and bring it right now,so off I went..when I got there the guy was truly interested in working on my amp and asked me all the questions about what the amp was doing,after that he said I did all the hard work getting rid of the Carbon on the pcb and wouldn't charge me his regular Flat Rate so for now I am just waiting..the guy was highly informative to me on Mesa amps and described what and how he would troubleshoot my amps problem(s) and fix it right up..so for now I am happy I made that last phone call to the small repair shop...more info later when amp comes home.