ROLAND BOLT 30- 60 cycle hum...

[Enzo]

It is the diode that makes it an RF probe, not the cap. A cap should work. A cap is what we use to turn an amp into a signal tracer. It isn't any different from a coupling cap between stages in a tube amp.

[oc disorder]

We may need an RF probe it's probably oscillating.....

So..I should print the bolt 30 schematic an replace all missing parts/jumpers?

Let's not go rushing in to this... I feel a bit stupid as I just noticed yours a Bolt 30 doesn't have the front panel switch and according to the parts list
there are differences on the pre board between the 30 and the 60 model.
However those diodes that replace the resistors do seem out of place.
On the pre-board layout the components missing from the Bolt 30 are shown as a dotted line outline.
First lets get a grip on what is going on.
Find all the changes not including the dotted line components.
By replacing all including the missing parts you would have a Bolt 60 pre-amp!
So make a list of all the changes and I'll attempt the same then we will compare notes.
I need to study the whole "shebang" a bit more.
If your happy to build the 60 preamp it probably will only be a few bucks and considering the circumstances
where we don't have a proper 30 schematic this may be the shortest way home.
And as Juan asked "Do any of the controls affect the hum?"

[czech-one-2]

OC [and everybody helping me here] you are really coming through on this, maybe I'll learn something if nothing else! :-)
Here's what I have found so far comparing my board to the Bolt 30 schematic [theres a 30 and a 60 schematic in the service notes]

R98 [Big carbon resistor, I'll call them BCR from now on cause theres 4 of them. I think you thought they were diodes in my high contrast photo] 10ohm /schematic 10ohm
R97- Jumper / not on schematic
R96 BCR - 10ohm / 10ohm
D13 pulled / not on schematic
D14 pulled / not on schematic
R95 BCR - 10ohm / 10ohm
R94 BCR -10ohm / 10ohm
R101 missing / not on schematic
c34 missing [I pulled it] , .0082 on schematic
Q14 missing / not on scematic
D14 missing / not on schematic
R86 missing / not on schematic
R76 missing / not on schematic
c50 missing / not on schematic
r44 missing / not on schem
r100 missing / not on schem

all good so far

R73 missing / 18k on schematic
C47 missing / .047 on schematic
c3 / c6 I pulled them as part of a mod to make the overdrive channel less muddy.
So, I think it is stock except for my clipping diode change and pulling of c34,c3 and c6. I'll probably put c34 back but it had no effect on the hum/buzz
However the c47 is missing and should be .047 and r73 is missing and 18k on the schematic, I didn't pull those.

If I need to purchase a better meter I will cause I'm sure some testing will be needed to find the source of the buzz.
This post is interesting as he's talking about hum and buzz in a Bolt 60, but I'm not sure what exactly he did - http://www.geocities.jp/dgb_studio/G_amp_e.htm

Oh, and heres the page where I got the idea to pull c3/c6
http://bolt60.no.sapo.pt/documents/m...nes%20mods.pdf
This again was to de-mud the overdrive channel, but had no effect on the hum/buzz

[czech-one-2]

And as Juan asked "Do any of the controls affect the hum?"

No, its not effected by any of the controls

[oc disorder]

While I'm still looking I'll give you some hands on stuff
lift one end of each R96 and R98 and also lift one end of R78 this is going to be a process of elimination.
That removes the power completely from the reverb circuit.
Try the amp for hum observe... then we will start dissecting the preamp e.g. lift one end of C10 and C11 or you can pull them right out this will disconnect
the first stage of the pre and part of the switching circuit.. try amp - observe
Try and do it so the tracks don't get damaged

[czech-one-2]

I would presume
it hummed more on the super dooper overdrive.............

Nope, overdrive or clean channel dont effect the hum.[trust me, nothing super dooper about it! lol ] Nothing effects the buzz really, its always there at power up and doesn't change.

[czech-one-2]

While I'm still looking I'll give you some hands on stuff
lift one end of each R96 and R98 and also lift one end of R78 this is going to be a process of elimination.
That removes the power completely from the reverb circuit.
Try the amp for hum observe... then we will start dissecting the preamp e.g. lift one end of C10 and C11 or you can pull them right out this will disconnect
the first stage of the pre and part of the switching circuit.. try amp - observe
Try and do it so the tracks don't get damaged

Will do tomorrow, getting late here and the wife and kids are sleeping and my weller station is in the bedroom...
I'll report back tomorrow. :-)

[oc disorder]

Ok I had my sleep.. after that with the amp off using the diode test function of your meter check the diodes.
A diode usually drops about .5 ie half a volt across it when conducting so as the meter conveniently provides
a test voltage - probes on one way = nothing = open circuit = infinity (as the diode is not conducting) reverse the leads and you should get approx .5
(volts) readout on your meter. The two diodes between VR7 and VR 6 are in parallel (reversed) so I suggest you lift one leg to check them both separately.
Maybe initially try it on any old diodes you have lying about so you know what to expect.

[The Dude]

In notice that you have the board dismounted for measurements. Is it possible that the board has become ungrounded because of this? Try running a clip lead from a known ground on the board to the chassis and re-measure.

[oc disorder]

The Dude.. He did a resistance measurement between ground on the board and the chassis

.3 ohms from pad#5 to the chassis ground point, power off

[The Dude]

The Dude.. He did a resistance measurement between ground on the board and the chassis

Missed that. THX!

[oc disorder]

I was wrong in my assumption that the board had been Modded .. and that the Bolt 30 & Bolt 60 had the same preamp.
It's the same PCB board but the 30 has less features - no effect loop pre/post selector and associated components and no front panel led's.
There are a few non populated positions in the Bolt 30 pre-amp.
Also there is a separate schematic in the zipped jpegs I'll post it here.

[czech-one-2]

Ok, lifted r96/r98/r78, no change so the reverb is eliminated.
All diodes passed the diode test.

With the chassis removed, the buzzing is worse until I touch a pot shaft and ground it. But even with grounding its still there.

[czech-one-2]

lifted c10/c11 - no change in the clean channel buzz but when I click on the overdrive channel VR1 the buzz dissapears.
There is not volume from the input [guitar] on either channel with these caps lifted.

[oc disorder]

lifted c10/c11 - no change in the clean channel buzz but when I click on the overdrive channel VR1 the buzz dissapears.
There is not volume from the input [guitar] on either channel with these caps lifted.

Ok I'm not going to analyze this too much other than to say I hope you can see what I'm trying to do here find the section with a fault.

The guitar signal passes through Q1 C5 and R12 to Q2 through C7 through the volume VR1 then up through the top "switch" then through C10 on to Q3.
There is also a second path it can follow where it doesn't go through Q2 this would be the clean channel .
Just below where C5 joins Q1 there is a path through C4 through the bottom "switch" then through C11 to Q3.
By pressing the footswitch the top switch is open and the bottom switch is closed. An "or" situation where the signal can go the bottom route for clean (excuse my loose technical terms) or through the top pathway or route with Q2 boosting for overdrive complete with a volume control.
Hope that makes sense.

Ok back to the chase for fun lets jump to the other end and disconnect C32 right near terminal 6 in the centre of the board.

I'm really hoping it will fall silent with this one as there is only one FET Q8 running from the 48volt supply here.
The next "interruption point" is the main in jack and we know it's silent after that !
Keeping my fingers crossed