Show Posts

This section allows you to view all posts made by this member. Note that you can only see posts made in areas you currently have access to.


Messages - ilyaa

Pages: [1] 2 3 ... 21
2
Amplifier Discussion / Re: Randall RM50 Channel Switching
« on: December 18, 2020, 12:14:35 AM »
dang that my only choice?

i dont want to wait till march!!

3
Amplifier Discussion / Re: Randall RM50 Channel Switching
« on: December 16, 2020, 06:47:43 PM »
hmmm

dang just not getting through -

im suspecting the relays - i can hear/feel one of them clicking but not the other (on the breakout/switching board)

but im having a damn hard time finding any of these:

SYS-S-112D -

any suggestions for suitable replace?? thank you!


4
Amplifier Discussion / Re: Randall RM50 Channel Switching
« on: November 20, 2020, 02:52:56 PM »
i guess maybe what would be helpful:

anyone here think they can explain how the channel switching is supposed to work in this thing?


5
Amplifier Discussion / Re: Randall RM50 Channel Switching
« on: November 20, 2020, 12:31:13 PM »
Quote
One would therefore assume that power for U2 comes from the 12v rail present on QC7 or QC8 on page 3.

i know and i have been assuming that! the only problem is: it doesnt!

with any amp like this, im assuming it worked properly at one point, so i dont think a connection has somehow magically disappeared! but since i am not getting +12V at the input of U2, and i cant even find where it WOULD come from, it makes the troubleshooting quite difficult.....

when i got the amp, the previous tech - who had got the amp to work but not fixed the channel switching, had rigged a little wire from QC3 on page 5 (the heaters of V2) to go over and deliver +12VDC to the input of U2. but thats clearly not how things are SUPPOSED to work.....so what the heck??

6
Amplifier Discussion / Re: Randall RM50 Channel Switching
« on: November 19, 2020, 11:23:39 PM »
hmm unless there is an error in the schematic, i do not see how that would go to the input of U2 on pg 6, g1.....

sorry to be dense, but how would it get there?

7
Amplifier Discussion / Re: Randall RM50 Channel Switching
« on: November 18, 2020, 02:00:29 AM »
hmm

page 3 Qc7 goes to:

page 1 Qc4
page 5 Qc3

the relay contact on page six goes to page 1 Qc7, which just goes to R2 - not +12VDC

unless im missing something i do not see how that gets 12V to the relay....


8
Amplifier Discussion / Randall RM50 Channel Switching
« on: November 17, 2020, 07:40:44 PM »
hey!

got an RM50 head on the bench -

things are working but it wont switch channels. there are some signs of 'boom' on the rear/footswitch/output tube PCB and someone has been in there before, but looks like they patched things up OK.

i am struggling with a specific issue:

see U2 on page 6 of the schematic - its a 7805 - i am not getting any voltage on the input, so, obviously, none on the output either. the problem is, im having a doggone time figuring out where the voltage on the input would be coming from in the first place. am i just missing something really obviousy?? im guessing itd be around 12VDC or so, but where the heck would it come from?

thank you!


9
Amplifier Discussion / Re: fender ultra chorus distortion
« on: August 20, 2020, 06:06:32 PM »
it's all moot now!

i had a FEELING i was barking up the wrong tree - joecool's early hunch was right!

after a ton of pointless tinkering, turns out C47 had come just evverrrr so slightly desoldered. argh! anyway, secured it and we are good to go - i knew it would have been something like that - whenever i find myself too deep down the 'doesnt make sense' rabbit hole, it turns out to be some mechanical nonsense -

thanks, guys!!

10
Amplifier Discussion / Re: fender ultra chorus distortion
« on: August 20, 2020, 02:11:00 PM »
Schematic I posted is correct!

11
Amplifier Discussion / Re: fender ultra chorus distortion
« on: August 20, 2020, 01:22:37 PM »
No dice -

U6 replaced, Q6 and Q7 replaced, C41 and C42 replaced, C89 and C88 replaces -

No change - man what is behind this?

The reason I suspect the effect itself is that if I turn the chorus trim pot I can hear the distortion getting worse as i turn it away from the center position in either direction -

12
Amplifier Discussion / Re: fender ultra chorus distortion
« on: August 19, 2020, 02:32:17 PM »
Haven’t found any similar complaints -

I’m not too familiar with chorus chips - here is what seems odd maybe:

The P-P square at pins 2 and 4 of the 3101 and 2 and 6 of the 3007 should be like 15V peak to peak but it’s more like 30V peak to peak -

I’ve got about 1VDC at pin 8 of the 3101 at pin 4 of them 3007. That ok?

It’s confusing because data sheet says pin 8 should be 14/15 of pin 3, but pins 1 and 3 are swapped in this design - with 1 being the supply instead of ground and vice versa with 3....

And at pin 5 and 6 - the input of the 3101 - there is some weird looking oscillation - but thats supposed to be there according to data sheet

Oh, and no noticeable ripple of low voltage rails

This whole thing feels like I’m barking up the wrong tree - but this noise is def chord related and it’s def bad!

13
Amplifier Discussion / Re: fender ultra chorus distortion
« on: August 18, 2020, 04:40:25 PM »
what a strange problem -

i replaced all the chorus-related ICs - checked for loose/cold stuff but didnt see anything

thought problem went away but it didnt.

so just to reiterate: amp works great but once you turn on the chorus effect any loud-ish transients break up in a very non-musical way. more like bad connection/busted speaker cone kind of way. but speakers are good and connections seem fine, too.

the chorus controls do not affect the issue - even with depth all the way down the distortion is still there. as soon as chorus is off it goes away.

the square waves at TP34 and TP35 have a little squiggly oscillation right at the top of each square.

when i scope the input to the power amps, it looks fine on both channels. clean sine wave on clean channel and chorus-y, wobbly sine wave on FX channel, but NO distortion. BUT the distortion is triggered by transients - so maybe i should put a square wave through the amp and see what that looks like...

the +/- DC bias to the op amps is a little high - almost +/- 18VDC when should be 16, but everything else in the amp works fine so im not really suspecting that....

any thoughts???


14
Amplifier Discussion / Re: fender ultra chorus distortion
« on: August 13, 2020, 02:09:38 PM »
its Clear the distortion is coming from the chorus effect -

If I mess with the chorus bias, I can hear it getting better or worse, but I can’t get it to go away. It kind of sounds like the chorus effects internal gain or makeup gain is too hot - but what causes this and how to repair?

15
Amplifier Discussion / fender ultra chorus distortion
« on: August 13, 2020, 03:00:10 AM »
hey!

got one of these:

http://www.electronicstudio.net/schematics/Fender/Ultimate_Chorus_Schematic.pdf

works great UNTIL i turn the chorus then -

the chorus itself works and sounds great, EXCEPT if i hit a note hard enough it gets this nasty sounding distortion. like the chorus effect is clipping - not good.

speakers are good - when amp is cranked w/o chorus on, sounds crisp and strong and clear.

any thoughts? not troubleshot an issue quite like this before.....

thank you!

Pages: [1] 2 3 ... 21