RM4 Problem is back

[JKD]

There's surely just a loose connection somewhere......does it still do this with both front and back inputs even when you plug straight in ( :lol: ) ?

 

[crankyrayhanky]

When the signal degrades I can snap it back by hitting the strings hard...Every module does the same thing...That must mean something....Of course I don't know what....Hoping one of you will...Something simple right???? PLEASE PLEASE PLEASE???

The rack is communicating "don't play like a sissy"!







Just kidding, hope you find the issue

 

[GtrGeorge!]

Matt....
any new info on this problem.
If it were me..Id get a tech on it..If you a decent tech (a trustworthy person) it should nt be all that difficult. But If you do it yourself you could very quickly get in over your head. Circuits are tricky. Even good techs argue about what does what in a schematic..Ive seeen that here at this forum..and we are usually laid back.
..so any news?
GtrGeorge

 

[Mattfig]

Hey,

Nothing yet...Although I haven't spent much time on the case over the past couple days...Problem is still there unfortunately...I'm gonna mes with it over the weekend...If I can't figure it out - there's an authorized Randall repair shop a couple towns away...

I'll givbe an update...Thanks for asking!

 

[m0jo]

Matt!

Remember that I had a similar problem and fixed it by cleaning the front jack?
Well it came back..

So after cursing the house down I took a look at it, and it turns out:
The jack pins were bent up by the jack that used to be in there for so long.
So it didn't make contact anymore to switch off the rear jack.

It will after ramming a jack in and out of the front a few times.

So see if that does it, if so you need the front jack replaced (easy surgery).

 

[GtrGeorge!]

Mojo,
I hope that solves the problem..
but I am skeptical. Usually a problem like a jack is a go or no go situation. Playing the guitar loud will not bend the contacts..unless maybe you are Superman..and then I am humbled, sorry to talk down to you..Superman.
Most likely its a component that is electroncally failing,imho. I think OkPete and Salvation are must smarter than myself at these things..but I have learned a lil over the years..and capacitors do these sorts of things. And I wonder if a failing Transformer would do similiar..not sure.
Anyway..I have a Randall Rm50 witht hte same problem..and I dont need it right now..so it sits with its lil issue. Strange though,
I let it warm up for 10..then power it off..then bring it up and THEN its good to go. So i thinks its a power capacitor..and they are very dangerous. So Im waiting for a nice pay check to fix this thing.
GtrGeorge

 

[eedude]

Fault isolation is key my friends. It is very, very difficult to take the system as a whole and speculate that C25 on B+ supply is probably the problem (just throwing an example out). Given the entire system I can rattle off probably one dozen things that it could be, and chances are I?d be wrong. Why, not ?cause I suck, but because the failure space is too big to speculate. Changing the tubes and the input jack are all fine, because that?s low hanging fruit and if it fixes it, then great off you go. But if low hanging fruit does not solve the problem, it?s time to divide and conquer.

Matt, here?s another idear for you. You are in the lucky position to own more that one unit. If it?s not too difficult, start subbing sub-systems between two RM4?s. I would start with the board that has V1 on it. The second one I would sub is the board that has the effects loop on it [Note: I do not own an RM4 and I?m speculating as to the internal sub-systems based on an RM100]. I picked these two first because these are the common paths for all signals.

Now, sub only one sub-system at a time AND button the enclosure back up, if the failure is aggravated by heat, the chassis need to be closed up or else the failure may not occur.

Once we know which of the sub-systems is failing, we can then dig into that one subsystem.

 

[m0jo]

Mojo,
I hope that solves the problem..
but I am skeptical. Usually a problem like a jack is a go or no go situation. Playing the guitar loud will not bend the contacts..unless maybe you are Superman..and then I am humbled, sorry to talk down to you..Superman.
Most likely its a component that is electroncally failing,imho. I think OkPete and Salvation are must smarter than myself at these things..but I have learned a lil over the years..and capacitors do these sorts of things. And I wonder if a failing Transformer would do similiar..not sure.
Anyway..I have a Randall Rm50 witht hte same problem..and I dont need it right now..so it sits with its lil issue. Strange though,
I let it warm up for 10..then power it off..then bring it up and THEN its good to go. So i thinks its a power capacitor..and they are very dangerous. So Im waiting for a nice pay check to fix this thing.
GtrGeorge

You'd think that, but actually the jack slowly bends back sometimes.. letting signal through. (also like I said when I poke a jack in there a few times it does as well).

Also I had this *exact* problem with my Laney, where the sound would come back when I played hard.
It turned out the FX loop jacks on the back where corroded and not contacting properly.
I stuck a jumper cable between them: voila, problem solved.
You may now refer to me as Superm0jo

I think it's a matter of having barely a contact and a big signal wil make it through, small signal will be pinched down.

@eedude: that is technically a good idea but the RM4 has these boards:
- front jack/channelswitch
- V1,2,3 tubes + modules (one large PCB that you an see when you look through the slots.
- power (transformers, caps etc etc).
- rear jacks (all on one board)
- midi

So yes you can substitute the small ones (jacks, midi..)
But the main and power board are the interesting ones. (they might be interchangable, but it would mean cutting a lot of tie-wraps).

Fig: if you're trying this: label all the cables properly!
that way it's easy to fix it all back together.

 

[Mattfig]

Wow! Awesome suggestions...Thank you guys! I have a number of things to try this weekend in my final attempt to isolate the problem...WIll post back any new info...THANKS!

 

[m0jo]

Wow! Awesome suggestions...Thank you guys! I have a number of things to try this weekend in my final attempt to isolate the problem...WIll post back any new info...THANKS!

Okay man, keep us posted
Another tip: pull the cables out by the connectors, do not pull on the cables themselves or you can imagine what will happen!

 

[eedude]

does anyone have picture of the inside of an RM4?

 

[m0jo]

does anyone have picture of the inside of an RM4?

I have some .. somewhere.. I'll look around for you tomorrow when I have time

Here ya go:

It's not perfect, but I can't find the better ones I shot..

 

[fuzzboat]

Most component failures are very "noticable" meaning their rarely if ever "intermitent"


I'll bet what your describing is most likely a "cold solder joint" issue - I worked in this field for many years and what your experiencing is very common to today's surface mount technology. (especially now that companies are being forced to comply to EPA standards and use the "new" solder that is eviromentally safer - the unfortunate reality of this is that "cold solder joints" are even more common than ever due to this change)

I haven't had reason to open up a RM4 but I'll bet the main PCB is 100%populated with surface mount parts (ie everything is minaturized and theres all these little tiny square parts !)

There are a few tricks to troubleshooting surfacemount PCB's - PM me if your interested Matt

Word to the Wise: if your new to troubleshooting and have limited skills the LAST thing you want to do is start attacking a surface mount PCB with your soldering iron - you can tear and rip off "pads" in litterally SECONDS !!

and GOD help you if the PCB is multilayered

 

[m0jo]

I haven't had reason to open up a RM4 but I'll bet the main PCB is 100%populated with surface mount parts (ie everything is minaturized and theres all these little square parts !)

Nope, full size components.
If Randall used SMT parts I wouldn't be playing their amps.
You can check by taking your modules out and peeking into the slots
That's the main PCB you see there.

This is not a computer, can you imagine what kind of noise a multi layered PCB would create with these signals?

 

[bruce egnater]

DO NOT go in and start changing parts...."willy nilli". Shot gunning is not an acceptable troubleshooting procedure. Does your model have a series loop? I assume you are doing this with nothing in the loops. Just guitar in the front and main out to the power amp?
1) You said you cleaned the front input jack. What chemical did you use?

I will be happy to help but I need accurate answers to my questions and you must do exactly as I suggest (when I do) please....OK??

2) If the problem occurs on all modeuls, the problem is not any one module so leave those alone. I assume if you put the modules from your other RM4 in this one, the problem still occurs??

 

[Mattfig]

Hey Bruce...Wow, help from The Man himself....I'm a lucky guy....Yep, problem occurs with everything plugged direct (tried both jacks for input)...On all modules...All 4 modules function just fine in other RM4s - just not this one...I will follow your directions to a T...

I cleaned the front and rear jacks using Deoxit...Lemme guess, bad choice?

Thanks Bruce!

 

[JD]

Good to see Bruce is spending his Saturday surfing the forum! Good to see someone who cares about us.
A Bruce story here...I remember many, many years ago listening to the radio (I believe it was WRIF in Detroit) and Ted Nugent was in the studio talking about and playing through this cool amp he had just discovered...an Egnater...it sounded awesome. Who would of thought that so many years later Bruce would still be the man when it came to amps!

 

[Daryl]

WOW... :shock: The legendary Bruce Egnater.
Would you be able to help out with some schematics for the RM4?
Please...

 

[ronstephens]

I had a similar problem in my RM4 last August (2010). Fortunately, it was still under warranty. When the closest authorized service center (Morgan Sound in Seattle, 150 miles away) couldn't pinpoint the problem, Randall (US Music) had him ship it to them. When they finally got to it, they couldn't resolve it either - so they replaced it with a new one. Except... first a new one had to manufactured!!! Then, they shipped it to the wrong place - even after we'd clarified that via telephone.

From shipping the broken one to receiving the new one took the better part of 4 months(!!!!). The new one had Ruby tubes (old one had JJ). Other than that, I can't tell any difference.

At first the guys at US Music were pleasant and responsive. Near the end they were ignoring me. Considering the wait time, that was not cool. On the other hand, the service guy at Morgan Sound could not have been better about staying on them, and keeping me in the loop.

 

[Bagoun]

Hi guys.
I think I have similar problem as Mattfig

The problem: when I was playing, after some time (sometimes 30-45mins) it just calmed down and seemed like all four channels were trying to work, but the diodes were lighting just like half way on each channel...and the sound was very very calm, disorted and fizzy...channels were unable to switch either by the button on rm4 or by midi controller...
When I shut it off and then on after some time it worked, but just for a while....next day it did the same thing...

Does anybody know whats going on?

Mattfig:
Have you solved your problem yet?
I'd be very lucky if you can post your working solution...

Thank you so much! I apreciate your help.