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fender stage lead 212 troubleshooting

Started by Capt_Dunzell, October 28, 2012, 06:02:52 PM

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J M Fahey

I think I have a working solution here, involving a single PFet (a J175 will do fine) and a 10K to 22K resistor, but I'm leaving to a friend's "asado" , but when I get back, after adding a couple pounds of charcoal grilled beef and a couple bottles of wine to my waistline, hope will have some neurone left to draw a schematic.

Capt_Dunzell

Quote from: J M Fahey on November 25, 2012, 11:29:13 AM
I think I have a working solution here, involving a single PFet (a J175 will do fine) and a 10K to 22K resistor, but I'm leaving to a friend's "asado" , but when I get back, after adding a couple pounds of charcoal grilled beef and a couple bottles of wine to my waistline, hope will have some neurone left to draw a schematic.

I didnt think I could be hungry again after dinner but looking at this got me hungry, hope was great!

It is a peavey module, the other module advertised is the kit form with a different chip.
The module I ordered did not come with a data sheet and I cant seem to locate on online so far.

Q1 is not on the mail board, it wasnt there at all when I opened it up, I saw a post somewhere that this was some sort of optional mute function?

Did fender have their own verison of a replacement? I couldnt seem to find one unless I have some search issues.

Roly

Ah yes, it's "barby" season here too.  {drool}  ;)
If you say theory and practice don't agree you haven't applied enough theory.

J M Fahey

Ok, the boa is back after having swallowed a cow ... or so I feel.

I think you can solve your problem this way, at least that's what I would do If I had it on my bench.

Being in Argentina I wouldn't even *try* to find a TL604, at any price.
This is not a general purpose TL604 replacement by any means (well, even Peavey's isn't either ;) ) but something which will solve your particular problem, in a Stage Lead (or the similar Studio Lead) amp.



The red dot I call C.V. , Control Voltage, is where voltage can take any of 2 values, enabling one channel or the other.
CV is fed through a divider from +15V : R39(820 ohms)/R41(682 ohms)+Led and can be grounded by panel or foot switch.

When open, it must sit around 8 volts; when closed it's 0V , of course.
Digital guys would probably call the 8 Volts a "logical 1" or a "high" and 0V a "logical 0" (duh !!) or a "low".

Now back to the Music World.

I know that on "low" (CV=0 volts) Q1 is a closed switch and grounds (mutes) signal at R9, meaning it mutes Ch2 (dirty), and think it must connect TL604 Pin6 , which is Channel 1 (clean) to Pins3+4 (output); at the same time it disconnects Pin7 (Ch2) from Pins3+4 , further muting it.

I forgot: Ch2 Led also turns OFF.

CV= High means the exact opposite: Led ON, Q1 open (Ch2 unmuted), Pins3/4 connected to Pin7 and disconnected from Pin6.

Argentine solution:

1) you say Q1 was not installed (a proper working TL604 means it's not *that* necessary).
OK, now we need it, get a J175 and solder it where it belongs.

2) get another J175 (let's call it Qx)and solder it to the TL604 pads, under the board (or you might plug it in the socket, but I doubt the thin Fet legs making good contact on those old worn sockets).
Source: Pin6
Drain: Pins3+4
Gate: Pin2 (control voltage in)

3) get a 10K to 22K 1/4W resistor (or even a smaller 1/8W one) and solder it from Pin7 to Pin3+4

4) enjoy.

Explanation:
I'm a dyed in the wool Functionalist, and for me, if it flies like a duck, walks like a duck, and quacks like a duck, it *is* a duck. ;)

Or in other words, if it mimics original Function close enough, it *is* enough.

Let's "test" it.

a) Foot/Panel switch closed. C.V. Low.
Led OFF
Q1 ON (Ch2 muted)
"Qx" ON (Ch1 enabled)
Note: I added the extra 10K to 22K resistor because Ch2 *still* is connected to Pin3+4, and setting R37 (Master) to 0 would mute also Ch1 ; the separation resistor I added takes care of that.
So: Ch1 ON, Ch2 OFF  :)

b) Foot/Panel switch open. C.V. High.
Led ON
Q1 OFF (Ch2 enabled)
"Qx" OFF (Ch1 muted)
So: Ch1 OFF, Ch2 ON  :)

Roly

A duck is a duck ... until you encounter a Lyrebird, ground dweller and superb mimic, not only of other birds but machines, camera shutters, human coughing, &c&c.

http://www.youtube.com/watch?v=WeQjkQpeJwY
If you say theory and practice don't agree you haven't applied enough theory.

Capt_Dunzell

I can do that, I will need to order some J175's the only FET that they had in the local shop was an MPF102.

Capt_Dunzell

Hoping the J175s arrive by tomorrow or Thursday, in the meantime an original Peavey adapter kit with the chip arrived today. Is it worth assembling to try or would the results be the same as the module that I already have?

Capt_Dunzell

Assembled the Peavy replacement kit and gave it a go....works perfectly! <3)

I think I am finally done thanks to everyones help!

Going to reinstall the chassis into the cabinet and give it some hours over the next few days.

Thank you everyone for all of your help, there is no way I would have been able to get this taken care of without it!!  You guys are the greatest!  :dbtu:

J M Fahey

Cool. Post its schematic for future reference.

Capt_Dunzell

It didnt have a schematic with it, but here is an image of the board and parts list.

:)

J M Fahey

Thanks.
Doesn't it come with some kind of instructions?
Maybe you can EMail Peavey, thank and congratulate them on their successful solution, and politely ask them for the schematic, because you want to understand it, not just mechanically solder.

DrGonz78

Also, in addition to asking for the schematic which I think I will try to ask them myself too. Where did you purchase this replacement kit? I mean I saw on that first site that there were no more kits available... That would be nice for others to know where you bought this... a link...

I definitely interested in the schematic to this board and anyone here too. You did Great work on this amp Captain. Could not do it without the great techs here (they know who they are) but you also played into the factor of the amp repair being successful too! Yup standing on the shoulder of others should feel great no matter how high you rise.
"A person who never made a mistake never tried anything new." -Albert Einstein

Capt_Dunzell

I attached the  instructions along with a picture of the kit in the previous post but for some reason it doesnt show up unless you click the link for the pdf.

I am reattaching the pdf file, it has the instructions, parts list, as well as some pictures of the circuit.

I ordered the kit from Antique Electronic Supply, they say that they still have them in stock.

http://www.tubesandmore.com/products/P-QTL604-AK

:)


J M Fahey


joecool85

I'm surprised Peavey even supplies such a kit, many manufacturers would tell you "tough, it's old, get a new amp".
Life is what you make it.
Still rockin' the Dean Markley K-20X
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