Solid State and "Noise"

[J Rindt]

I am working on my friends Marshall Valvestate 65r.It hums very loud as soon as the amp is turned on. The hum is present with or without a guitar plugged in. The amp seems to function "normally" except for the noise.
Is the Hz setting on a Multi Meter a kosher way to measure noise.? Hooked to the speaker jack, my DMM says 120 Hz.I double checked the grounds and input jack and chopsticked everything.I replaced C11 and C12 in the power module. They were actually 3300uf at 63V.I also replaced the two 22uf at 450V caps for the One 12AX7. I tried a new tube as well.
None of that has had any effect.
The only parts that show signs of heat are.....ZD-1 and ZD-2C11 and C24.
They are right near the Power Tranny.
Do transistors get "noisy".?
Can the driver and power transistors cause this.?
Thank You
https://el34world.com/charts/Schematics/files/Marshall/Marshall_vs65r_65w.pdf

[shooter]

Do transistors get "noisy".?
Can the driver and power transistors cause this.?

yup and maybe
I worked on 1 VS at least 3 times, one of the bigger modern POS amps ever for repairing!
I told the client to sell it or trade cause I wasn't opening it up EVER, also turned down repairs on 2 since
I would start by re-soldering everything, then cleaning and re-tensioning every connector, probably need at least 2 or 3 pots.............................

[terminalgs]

I don't know anything about Marshall valvestate and I'm no SS expert.   I do know from working on old Kustoms that if ground isn't exactly centered between your SS circuit's power supply's +15vdc and -15vdc, you get hum (i.e.  you have +15.5vdc and -14.5vdc...)

[92Volts]

120hz sounds right. That's the noise you'd expect from full-wave rectified 60hz power.

I guess transistors could get noisy, but like tubes I'd expect "random" noise-- i.e. white noise-- or with tubes, noise picked up from surroundings (microphonics). An active device wouldn't randomly produce noise at the same frequency as power supply ripple.

So what's happening is either: Too much power supply ripple, or circuit failing to reject/cancel power supply noise. If transistors are used in a differential setup (this is used inside opamp ICs, but not only there) and one fails, you lose the differential effect and noise rejection ability.

While you did replace power supply caps, I guess a circuit board trace could be bad, leaving them unconnected. But considering the work you've already done, power supply problems seem unlikely.

It sounds like you don't have a scope, maybe you could short the signal to ground at different locations, to determine where in the circuit this sound first occurs? You'd really want a schematic before doing that, and I can't guarantee this is safe in this amp. But some sort of signal-tracing would be helpful.

[J Rindt]

Yes, i do have a scope.I am not super skilled with it. 
I THINK i can figure out where the signal enters and then exits a transistor. Would i simply put a 1k (or whatever) signal into the amp and then follow it from the input.?

[shooter]

my DMM says 120 Hz.

it's only got 1 tube, did you swap it
retention the socket
re-flow the solder joints
look at the schemo, pg1 upper right, there's a connector W5-8 - retension
same area, C6, measure Volts AC from the cap + to chassis ground, whatcha get

[PRR]

> The only parts that show signs of heat are.....ZD-1 and ZD-2 C11 and C24.

So replace them all.

They aren't noisy. They have quit damping the 120Hz from the transformer rectifier.

If they pass buzz, they are probably failing to clamp the voltage and you may have a LOT more than 15V at your "15V" points. This can blow-up the op-amp chips.

Fenders have a similar sickness but it usually shows as toast around resistors doing what R17 R18 do for Marshall. Examine these.

[J Rindt]

10-4
Thanks Guys.I will give this stuff a shot as soon a i can.....and report back in a few days. Thanks Again.

[J Rindt]

We have been caught up in all these fires in California.......on page #1...C11 and C24...does that say 220n...0.22uF for the capacitor value.?  It is very hard for me to read the schem.Thank You

[shooter]

yup

[J Rindt]

Great...Thank You
Just ordered some parts from Mouser.

[shooter]

If you're gonna be a VS expert, I've attached another schematic, fwiw

[J Rindt]

OK.....I have Massive family problems. LONG Story, i have had to care for my 81 year old Mother In-Law all of a sudden.But.........i replaced the Zeners and the two 0.22uF  caps.The original caps were Super Small.!.......like 20x smaller than the new parts
Is that because they were those Tantalum type caps.?  The new caps are just "normal" capacitors, but they fit.I do have +/- 15V across the new Zeners

Anyway.....the noise is still the same but now i get no guitar signal out.Right at the Input to the amp, D-7 and D-8, i get 15V at D-8 but only 0.5V at D-7. This is with no guitar plugged in. Is there any chance that is normal for some reason.?
And again, i only have a basic knowledge of tube schems, Solid State is a challenge for me.Diodes D7 and D8, on the schem, one side of each diode simply terminates with a line at 90 Degrees.
Does that just mean it is connected to the main +/- 15V supply some where.?I am not used to seeing that on tube schematics.Thank You

[sluckey]

D7 connects to +15V, D8 connects to -15V. The junction of the diodes should be zero.

[J Rindt]

When you say Junction, is that in relation to Ground...one probe at D7/D8 and the other probe on Ground.?

[sluckey]

yes

[J Rindt]

OK.
With the black probe on ground i get.....
Cathode of D8   +15.0V
Anode of D8      +0.35V
Should that Junction (D8 Anode) be closer to 0.00 Volts.?

[sluckey]

I think it's probably fine. Those two diodes simply clamp the input signal to +15V. Is JS1 the guitar input jack? If so, I don't see a purpose for those diodes unless it would be for protection in the event someone tried to plug in some very high level signal source.

[J Rindt]

Yes...Single/Main input jack.
So as to why i have no output.....
I am not great with a scope, especially with Solid State, but i do own one and a Sig Gen.
Should i put a signal into the front of this amp and see where i lose it.?
Or are there More/Simpler things to check first.?
Thank You

[shooter]

things to check first.?

did you have to unplug connectors to solder in parts?
if so, re-check making sure you didn't "slip" a pin
pick a couple ic's and just verify your +/-15 is at everyplace it should be, I sorta do a left mid rght random checks and if it's where it should be I move on to siggen n scope

I circled 4 test points below
scope your sig-gen, set it up for ~~ 300mV PP, (hot signal)
once you're happy, have it synced, plug it in and probe the TP's.  TS & vol should be centered.

[J Rindt]

things to check first.?

did you have to unplug connectors to solder in parts?
if so, re-check making sure you didn't "slip" a pin
pick a couple ic's and just verify your +/-15 is at everyplace it should be, I sorta do a left mid rght random checks and if it's where it should be I move on to siggen n scope

I circled 4 test points below
scope your sig-gen, set it up for ~~ 300mV PP, (hot signal)
once you're happy, have it synced, plug it in and probe the TP's.  TS & vol should be centered.

Oh wow...thanks for all that.Yeah, this is a typical, "Cheap" solid state amp. Almost like looking at the inside of a computer.
There are a couple of Molex Type connectors and i will do the best i can to make sure those are OK.
I hate these scenarios.
The face-plate is at a 45 degree angel, and you kind of have to man-handle the board to get it in an out of the amp each time.
These amps seem like they were made to never be repaired. All the spade connectors were crimped, onto the terminals, Super Hard. So they would no come off after the sale no doubt.
But i just about had to take a dental pick to each one, and spread the lugs a bit, just so i could slide them off the Transformer/Switch terminals.
For me anyway, there is a constant worry that something might break each time i take one of the boards out. The little solder pads just about jump off the board if they even see a soldering iron.
Stuff like that, if you know what i mean.?
I am used to working on Hand-Wired Turret and Eyelet boards.....stuff that can be soldered and desoldered, several times, with relative ease.
Anyway......thanks again fro that great Test Procedure.
I will go at this again tomorrow.
Thanks Again

[J Rindt]

I have the scope set up.
300mV at 700Hz.  Not sure if the frequency matters or not.But before i get into that.......

Probing IC-2 i get +15V on pins 1,3,5 and 8.
IC-5 shows +15V on pin 1 and 8. Shouldn't there be negative voltage also.?
I have the meter set to VDC, with the black probe on ground.
Back on page #1 of the schem i have +/- 15V on diodes ZD-1 and ZD-2

[sluckey]

IC2 should have +15 on pin 8 and -15 on pin 4.

IC5 should have +5.6 on pin 16 and -5.6 on pin 9.

[J Rindt]

IC2 should have +15 on pin 8 and -15 on pin 4.

IC5 should have +5.6 on pin 16 and -5.6 on pin 9.

I might not be reading these correctly. 
 Looking down on the IC.......at left is a "half moon" in the plastic body. Also there is a circle at the lower left.
I was assuming that circle locates Pin-1...then going to the right is 2,3,4.
Right above 4 at the top right is Pin-5...Pin -8 would be the top left.
With that in mind i get
IC-2

1- 14.5
2- 0.2
3- 14.2
4- 0.78
5- 14.3
6- 2.3
7- 000
8- 14.9
These are all positive  numbers.

The same thing with IC-5.  But it only has Eight Legs.  There is the half-moon again but the circle is in the middle of the IC.
1- 14.5
2- 0.3
3- 6.9
4- 0.7
5- 000
6- 7.0
7- 0.23
8- 15
And again these are all positive voltages.

Sorry if i am doing something wrong.....
I appreciate all the help.

[sluckey]

All DIP chips (no matter how many pins) follow this scheme...

https://en.wikipedia.org/wiki/Dual_in-line_package#Orientation_and_lead_numbering

[sluckey]

The same thing with IC-5.  But it only has Eight Legs.

Are you sure about the legs? That IC is a 16 pin DIP chip. If it only has 8 legs then someone cut the others off. The schematic clearly shows pin 16.

http://www.onsemi.com/pub/Collateral/MC74HC4316A-D.PDF

[J Rindt]

OK.
I AM Reading the pin numbers correctly.
And there are No Positive voltages on these two IC.

Regards IC-5.....you are looking at page 2 of 3 on my schem link.?

IC-5 only has 8 legs.
I would have to go look at the board, but i think it is IC-1 that has 14 legs.
Am i looking at the wrong part somehow.?

[sluckey]

Haha! I've been looking at the schematic that shooter posted. It ain't nothing like the schematic you posted. Please disregard my previous posts about voltages and pins.   

Yes, IC5 has 8 pins and there should be +15 on a pin and -15 on a pin, just like the schematic shows. Those ICs won't work properly unless they have both voltages.

[J Rindt]

No Problem My Friend.....

So let me ask this.   I obviously (i think) have a problem with the +/- 15V supply.?
If we look at Page #1 of the schem...Diodes ZD-1 and ZD-2...is that more or less the beginning of the 15V supply.?
As i say....... i do have +/- 15V THERE.
Would it make sense for me to try and follow it forward from that point.....see if i can find where the NEGATIVE 15V is disappearing to.?
Thank You Again.....

[sluckey]

If we look at Page #1 of the schem...Diodes ZD-1 and ZD-2...is that more or less the beginning of the 15V supply.?
As i say....... i do have +/- 15V THERE.
Would it make sense for me to try and follow it forward from that point.....see if i can find where the NEGATIVE 15V is disappearing to.?

Yes, ZD-1 is the source for the -15V and ZD-2 is the source for the +15V. Are ZD1 and ZD2 located on the same board with all the ICs? I would follow the -15V path from ZD-1 to each of the ICs that should have -15V. Look for a break in the pcb trace, or maybe a bad solder joint if any jumpers are involved. (see pic)

[shooter]

the schematic that shooter posted

sorry,     I have one more version if you need more confusion, I think Marshall patterned this after the GA-5s 

[sluckey]

I jumped on that schematic because it was more readable. Never even considered it was a different amp. Hey, I'd still be using it if the 8-legged IC5 had not come up! And I'd still be wondering why everyone else was so lost!   

[shooter]

I was right there til reply 14 when you guys were talking D7/8, then I pulled up all 3 schematic of the amp and started laughing thinking Marshall hired some downsized engineer from Gibson 

[J Rindt]

Yeah, i will do that ASAP.Dealing with MAJOR In-Law troubles at the moment. 
Won't mention it again.......
Yeah, i cannot really find a schem that i can actually READ.....but i get your gist.
Those Molex connectors look like they use 128 AWG Wire. 
I might be wise to do a continuity check on those if they are involved.

Anyway.......thanks again.  I will give a shout as soon as i know something.
Thanks So Much.!

[shooter]

Those Molex connectors

I've been under the hood of 3 of these things, the 2nd? one every board connector was 1 pin off, burnt traces, loose wires, I turned it down, the other 2 I fixed and told the customers, SELL THEM, cuz I ain't going back in there, they did 

extra, IIRC there are 3 official revs of the 65W, and I believe 1 unofficial version, and again been a couple years, I think the revs were counted like the traveling wilburys 1 3 

[J Rindt]

Yeah...Oh-Boy.
I am certainly NOT an amp tech, but i have worked on enough Good Amps to know how lousy this thing is.
I am sure it has been said 100 times before, but.....these things were never meant to be taken apart and repaired...No doubt they function past the warranty period, and then Marshall does not care what happens.

Should be no surprise, but this was my fault...The amp "works", then i replace some parts, then the amp no longer works...The Pads and traces are paper thin... Plus these diodes ZD-1 and ZD-2 had been getting very hot, so i replaced them and their corresponding caps...No doubt the heat was hard on the traces/pads...The pads fell apart as soon as they saw my soldering iron...It seems the trace was cracked...maybe 10mm after the pad...There was no continuity between ZD-1 and D-5...but there was when i pushed down on the board.
Is it called "masking".?....i need to scrape some off and bend the lead of ZD-1 down onto the exposed copper trace...Etc etc etc.

I probably should have been able to figure this out myself, but.....Solid State always confuses me, and i have not worked on amps much in the past 2 years...since i got back into photography.
If i can get this back to how it was when the kid gave it to me, i am simply going to give it back to him.
Even the Vox CC amps were pretty good quality PCB... not to mention the Soldano, Fryette and Fuchs i have worked on.
These "beginner" types of guitar amps.....its too easy to break something when you are trying to help somebody, at least for a Amateur/Hobbyist repair guy like myself.
I do not want to see another one.
Hopefully this will "fix" it.
FWIW...i will let you guys Know.

Thanks Again for everybody's efforts.
You saved me from a nervous breakdown 

[sluckey]

So, is it fixed now?

[shooter]

You saved me from a nervous breakdown

hang in there, if you're good it'll happen 

[J Rindt]

Yes, it is "fixed".....back to the condition it was in when i got it. I appreciate the advice on scoping this amp to find the hum.....but i am going to quit while i am ahead...I have no desire to remove either of the PCB again.
I wish i could be more help to the kid, but he can find lots of similar amps on Craigslist.
Thanks Again for all the fantastic help.! 

[shooter]

there are ALOT of great "plexi-ish" designs here, when he gets his $200 bucks tell him that's a good start for a real amp 

hopefully you gained both knowledge AND wisdom 

[J Rindt]

hopefully you gained both knowledge AND wisdom 

Yes i have. I am not going to work on cheaply made amps, that are out of their warranty, and only "worth" 100 bux.
How many 10-15 year old Fender HRDlx are floating around.....A Million.?
Not sure i ever want to see another one of those again either.
I will leave that stuff for you Real Amp Techs.