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Post subject: Re: 93 blues deville fried diode- long winded..
Posted: Mon Feb 14, 2011 8:58 am
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Good idea to take a break, it almost always helps. When you get back to it, try to be more methodical in your troubleshooting. When you jump around and just randomly try things, you'll be chasing your tail and may never know what the problem actually was.

When you say that all of the DC voltages were to spec (besides the TP26 reading), or close, then there is no further need to replace anything in the DC supply, such as the zeners, etc. Again, if no voltage at TP26, then check the Y voltage at the cap. If you have the Y voltage, then the problem is between the Y voltage and TP26 (or even V3 tube). If you have B+, X, Y, Z, C-, and the +/- 16 volt supplies, then your power supply is good, look in another area, don't replace working components.

Plugging directly in to the Power Amp In bypasses the preamp section, and bypasses the ICs, so no reason to replace those. Plugged directly in and still no sound tells me that the problem is in the V3 and/or output tube section. And, when you just start replacing things for no reason, you can actually cause more problems. FORGET ABOUT THE ICs, THEY ARE NOT THE PROBLEM.

You'll find that the KISS principle is the best, don't make it out to be a huge problem, simplify as much as possible. I know that you have a lot of info to digest, but take it one step at a time, develop a procedure for the best results. :idea:

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Post subject: Re: 93 blues deville fried diode- long winded..
Posted: Mon Feb 14, 2011 9:04 am
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Richardo, I know what you mean. I remember this Peavey Classic 30 I tried to revive. It had this one EL84 that would runaway, no matter what EL84 tube or what static readings I got.

Luckily, I had access to a working Peavey Classic 30 and just substituted the boards. After looking and looking at the bad board---which is actually 3 boards bent around each other and tied together by what seems like a bazillion jumper wires on each edge---it seemed that several jumper wires were damaged and had lifted the tracings that supply bias voltage from the main PC board to the board with the power tubes. But, just to pin 4 of V5. If you look at the layout, you can see how daunting it is to find the wire trail.

And what made it worse, is the tracing/wire issue was not consistent. Sometimes the amp would work fine for months. Then, POW! it work blow that one EL84. So, sometimes the readings were fine and finally ONE TIME the reading were not.

Take a well-deserved rest. Report back, if you can.



Peavey 30 schemo and layout:


http://www.blueguitar.org/new/schem/peavey/c30schem.gif


http://www.blueguitar.org/new/schem/peavey/c30layg1.jpg


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Post subject: Re: 93 blues deville fried diode- long winded..
Posted: Mon Feb 14, 2011 9:23 am
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BMW2002Ti wrote:
Richardo,

Sorry if you answered this already... but are you getting rock steady (+ & -) 16 VDC off the part of the PS supplying the IC chips? The same circuit that diode CR20 initial blew, in the first post? It's not uncommon for the zener diodes (CR22 & CR23) to blow, which can lead to damage up & down stream of the blown zeners.

My WAG is that either U1A on U1B (TL072 chips) or circuit tracing could have been damaged when CR20 blew. No signal maybe getting through to V3 because of this. Therefore, no TP26 voltage, which maybe dependent on signal onto the grid of V3 (12AX7 PI).

JOC... did you have any symptoms with your amp... just before the CR20 diode popped?


Hi BMW.... tested this all yesterday and all was good in the dc department... but something else is not right in the areas Shim suggests.

We did + side of C43 16v and - side of CR21 -16v... checked V1, V2, V3 @ pins 4 & 9 all good 6v...
When I have a rest for a bit, I'll go looking in the areas shim suggests...

The amp did act up one time late last year dropping out, loosing volume. I turned it off and it was fine again after it cooled down... worked perfectly for quite a few gigs leading up to Xmas.... it did the same thing this night at practice..... couldn't use the clean channel, but used the drive channel..... after practice let it cool down then opened the back up and had a look.... powered it up again then I smelt the ol' smell... something was beginning to burn... shut it down and didn't try it till the morning... yep, the diode was cooking....

Geezzz, sounds like fun with your Peavy...... I don't think!!
Yeah, better when something just blows out, rather than be intermittent..


Any way, I'll get back to you guys on how I get on...
In the mean time be nice to rest my brain...

Thanks again for your input and support..
Muchly appreciated.

All the best
Rich

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Post subject: Re: 93 blues deville fried diode- long winded..
Posted: Tue Feb 15, 2011 8:44 am
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Hey Ricardo,
Contact Ken Fox, Fox Vintage Amps, he knows what your problem is or at least how it started.
Good luck,
90ML


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Post subject: Re: 93 blues deville fried diode- long winded..
Posted: Tue Feb 15, 2011 10:49 am
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And C- reads a steady -49-50VDC?

Since CR20 diode rectifies the circuit supplying voltage to the IC chips.... me is still wondering. Maybe check points #4 # 8 of the TL072 chip just before the pre-out. Chips can be kinda sensitive, so the readings shold be close to 16VDC (on #8) & -16 VDC (on #4).

Something drew excess circuit through CR20 and popped it. Maybe something in that clean/drive circuit. Or that TL072? Or bad/lifted circuit tracing(s).


Good luck. Keep on keeping on...


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Post subject: Re: 93 blues deville fried diode- long winded..
Posted: Thu Feb 24, 2011 3:44 am
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Hi all.
After collecting some 'head space' on this issue, taking things step by step and re reading back through all the good advice, plus feeling a load more comfortable with dealing with 240ac and 500 dc voltages, and, knowing where I'm going and what to look for.
I think I've located the problem.

First off, since B+, Z, Y, X and -C on the main PCB board all have the 'in the ball park' dc voltages. I then went to the valve pcb and went through the test points here where these currents occur.
The problem child as mentioned by Shimmilou as being the place to look, around my incoming 'Y' voltage.
OK.... here's the thing, when I changed out all the caps, I also did R51 plate load resistor, after I soldered it in, I couldn't remember if the leg of R51 was suppose to be connected to the 2nd wire on the 6 wire strap which returns to the main PCB. So I made sure it wasn't!
Now, looking at the schematic, at the junction of R51 & 52 on the valve board, where the Y voltage is measured, it shows the little arrow that goes no where.... this is then picked up on the main pcb going into C45... with the little arrow that goes nowhere.(obviously now I know, they link up).
I physically traced the 2nd wire from the strap on the valve board to the main board and it led right to the capacitor C45 where the Y voltage comes from.

So what I'm asking, is this correct and I need to make sure the leg of R51 and the 2nd wire connect??
So what I can assume, this is the only way that the 'Y' power supply comes into the valve PCB from the main board and C45??


OK folks, please let me know asap and I'll get it soldered and get this lil' deville crankin'

Wait for your reply..

All the best for now
Rich

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Post subject: Re: 93 blues deville fried diode- long winded..
Posted: Thu Feb 24, 2011 4:32 am
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Richardo,

Yes, the "Y" point off the power supply (C45) should connect to the "Y" arrow next to the (V3) 12AX7. At that point, the VDC should read around +413VDC. Be careful, here as C- (bias power supply) maybe physically close to this Y point. C- MUST measure around -50VDC. NOT POSITIVE.

You'll note this C- point has two 220K-1/2 watt resistors tied to it.

Good luck with all that. Keep us posted.


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Post subject: Re: 93 blues deville fried diode- long winded..
Posted: Thu Feb 24, 2011 4:59 am
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Hi Bmw,
I did do a check this afternoon on the valve board to all points of incoming power to make sure. I had good C- power being supplied in between R53 & 54.
The reading was -54vdc.

So I'll do the little soldering job now and put the board back in the cab.

I'll let you know how I go in an hour or so.

All the best for now
Rich

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Post subject: Re: 93 blues deville fried diode- long winded..
Posted: Thu Feb 24, 2011 6:57 am
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IT'S ALIVE, IT'S ALIVE.....
Wooo hooo, man it's just great to hear the ol' girl again. Warm and rich. Even warmer than it was before. :D
Have all the replacement JJ's in and all good so far, very low noise.

Ok, while the clean channel is working wonderfully. Just been playing it for the last 20min... reverb's working well too.
However, yeah, aint it typical.... When kicking in the drive channel, both from the foot switch or the manual switch all sound cuts out.
Ok, have previously checked all op amps U1-4 and there was 16v on all pin 8's and -16v on all pin 4's if this helps any.

Mmm, if I knew back 17 years ago what I know now, I would have just bought a single channel tube amp.... the only time I've ever used the drive channel was really with jamming when I couldn't be bothered bringing my effects peddles along or when our band was playing some Ry Cooder stuff... really I just use double tube screamers, chorus and delay....

But I guess I better, once again ask for your solid advice on where to begin with this next round....... with the 'devil' in tweed..

As always, appreciate your vast input.

A huge thanks you guys for the patience, you've taught me heaps in the past weeks.. talk about a crash course in sorting amp shite out..... truly, you guys are just great!!

All the best
Rich... (a very happy chappy... :D )

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Post subject: Re: 93 blues deville fried diode- long winded..
Posted: Thu Feb 24, 2011 7:23 am
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Very cool! :D

Ry Cooder covers? My hats off to you. Another one of those multi-talented guitarists I dig is David Lindley. I got to play a bit with his brother Peter. The whole Lindley family is quite talented.

I'd check the bias a couple of times over the next few weeks, as the power tubes settle in.

Have fun! Glad things worked out well.


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Post subject: Re: 93 blues deville fried diode- long winded..
Posted: Thu Feb 24, 2011 8:02 am
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Ahh, yes, the man who loves polyester :lol: I love David Lindley.. the guys just a legend.
So you sure are in great company 8) Lucky man!!
The first time I heard his talent was with Jackson Browne.. just such a soulful lap and slide player.. and mandolin (not to mention doing the Franky Valley type falsetto in JB's 'Stay') besides all the other instruments he can play... sort of fits in with Jackson (the soul of world imo)... Then when he came out with the El Rayo X album in 1981... I think it was his rendition of Mercury blues..... man, I was about 20 living a partying life style, this was just wild... had to have the album... Tu bur cul los sus blues... what a classic !!

Also love Los Lobos.. Wilco, but then I love metal... maybe a bit of country but not too far south :)) and my original love that got me playing when I was 9 was blues.. all the British bands in the 60's then back to the original players of those classic songs.. then CSNY, all the harmonies in all the bands before and after... so many great guitar players amongst so many bands and the list just goes on and on..... so much music..... we're lucky to share in such a wonderful outlet...

As for Ry Cooder stuff, my double stop playing to his masterful playing of 'little sister' certainly sounded pale :)) gotta hate those out door gigs where the fingers are frozen!

Ok, cheers for now BM...
I'll have to hunt down this issue with the drive channel, but not straight away, gonna enjoy some sweet tone first.

All the best for now
Rich

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Post subject: Re: 93 blues deville fried diode- long winded..
Posted: Thu Feb 24, 2011 10:08 pm
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richardo wrote:
IT'S ALIVE, IT'S ALIVE.....
Wooo hooo, man it's just great to hear the ol' girl again. Warm and rich. Even warmer than it was before. :D ....However, yeah, aint it typical.... When kicking in the drive channel, both from the foot switch or the manual switch all sound cuts out.
Ok, have previously checked all op amps U1-4 and there was 16v on all pin 8's and -16v on all pin 4's if this helps any....


Cool, making great progress. Now you might be back to your original channel switching problem. :?: Just to cover all bases, the Master Volume pot and the Drive pot have to be turned up for the drive channel (gotta make sure, sorry). Checking to make sure that you still have the +/- 16 volts at the pins of the chips, might be a great place to start, even though you checked them before. And make sure that each voltage stays fairly constant when switching channels. If both + and - 16v supplies are steady at all of the chips, then the supplies are good, which are used for channel switching chips, reverb chip, and the Power Amp In and Preamp Out buffer chip. There are no chips in the signal path, except for the reverb. If the reverb works, and the channels switch, then the chips are all likely good.

I suspect that if the 16 volt supplies are good, you may have a bad/sticking relay (or bad solder joints on the relay), RY2 but could also be RY1. A bad relay could very well account for your CR20 and 21 diodes frying to begin with, especially if the relay is sticking and drawing too much current. A bad relay could also cause the drive channel sound to drop when switching channels. Just a couple of things to check. Let us know what you find. :)

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Post subject: Re: 93 blues deville fried diode- long winded..
Posted: Thu Feb 24, 2011 10:37 pm
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Thanks Shim for chiming in......
I will check the voltages on all the op amps over the weekend.
I guess I would be specifically looking for voltage drops on U3 being the ic related to the clean and drive channels for switching from clean to drive?

If all looks good will I guess replace the two relays..??

Thanks so much Shim for helping me get this far...

Will report back on my findings...

Thanks for this, gives me something to go on.

All the best for now
Rich

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Post subject: Re: 93 blues deville fried diode- long winded..
Posted: Fri Feb 25, 2011 9:49 am
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Well, if the 16 volt supplies check good/steady (even while switching channels), you can check the relays operation with your meter before replacing them. It is just what I suspect, not that I'm sure that they are bad. The two relays basically switch the Volume pot out of the circuit, and switch in the Gain and Master Volume pots into the circuit. Note the test point readings at the output of the two relay switching chips (U3, U4), at TP31 pin one of U3, TP 32 pin seven of U3, and TP34 pin one of U4. These test points should switch between about +15 VDC to -15 VDC when using the channel select button (negative lead to chassis as before). If the TPs are good, next would be to check the relays operation to see if they are actually switching in and out.

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Post subject: Re: 93 blues deville fried diode- long winded..
Posted: Fri Feb 25, 2011 8:33 pm
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Hi Shim,
have retested all the chips.. all good voltage to both pins 4 & 8 when changing from clean to drive.

I did the test when switching from clean to drive on U3 & U4's TP's here's the results..
U3
TP30 (Pin2) Cln=+1.99dc Drv=+.04dc
TP31 (Pin1) Cln=-15.36dc Drv=+14.12dc
TP32 (pin7) Cln=+15.32dc Drv=-14.11dc
U4
TP34 (Pin1) Cln=-15.56dc Drv=-15.53dc

So does look as if TP34 is not switching from negative to positive, possibly the fault??
I have a PC4560 ic on hand so can change this out straight away.
By the schematic it looks as though U4 is for reverb only?? The reverb is working no worries on the clean channel.

Also, when I dial up the Variac to running voltage with power on and on standby, I can here the relays switch, backing off the power they switch back.... is this ok?


Thanks again, and here from you soon
Rich

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