Peavey Mace VT Series - blowing fuses

[Enzo]

I don't know if I can maintain focus, but...

No phasor. Like a tremolo, you have an LFO and you have the effect circuit. So see the RATE pot, center right? That is the LFO with U11, U12. DO you have an LF oscillation at that control? U7-10 are the phase shift bucket brigade delay line. See how the signal from the LFO control goes to pin 5 of eaach? Your effects channel works otherwise, right? So there ought to be signal at the post control R57. Buffered by U1B, then through R63 and on to the power amp. But that U1B also snakes around to the inputs of U7. So is the channel signal present at pin 6 of U7? And U 8,9,10? That processed signal is then routed through TL604 U13. Swap it for the one in the reverb circuit, or even just replace it with a jumper wire from pin 7 to 3. - that leaves the phasor on. Not that I leave it that way, but it till tell you if that IC was bad.

Don't let the symbol fool you, the signal goes IN pin 3 and out pin 7. That goes down to R64, wher it mixes with R63 and on to the power amp.

If the LFO is bad, I dod suapect those two tantalum caps. And up by the TL604 is one of the several 2uf/35v caps in this preamp. I'd replace every one of them.


U14 is the preamp channel out feeding the post control. it is a 478 type (70487478), and since the channel works, we know that IC works. U7-10 are also 478s. You can pull them one at a time and sub them into U14. If the channel still works, then the IC is good.

[Tone Meister]

No oscillation at the R57 RATE pot, so following Enzo's comments above determined that the 70487478 at U11 was bad. Borrowed one from U15 and now have the Phasor working through to the speaker. Thanks Enzo, as usual you were all over it. Apparently you don't need to maintain focus to out-think the rest of us.

Now to find a replacement for that 70487478, which is a CA3094 and obsolete. Have been on the phone with Peavey a couple times already today but haven't tracked down a substitute yet. At one time the replacement was an LM3080N but now that one is obsolete as well. They do have an "adapter board" pt#39095750 that will not work in the phasor circuit but does work elsewhere in the preamp, but it costs $14.99 + shipping! So obviously I'm looking for a workaround if one is available.

One parts person mentioned a company called UW Tech with an exact replacement substitute part #9E08-0103-0800-10 but an internet search draws nothing but blanks.

Since I now have the Phasor circuit working, does anyone know of a suitable substitute for the CA3904, LM3080N that will working in the preamp section of this amp, more specifically U15 in the preamp? (70487478 is the Peavey part number)

[Enzo]

So their workaround won't work on the phasor, but will elsewhere in the amp? You already stole a part from elsewher to make the phasor work, so install the workaround where you stole that part.

$15 sounds like a lot, but really, it installs right in place of the orriginal. I look at labor as having value, so how much time do I spend trying not to spend $15 to get an amp back to its owner?


I have six of the original parts, but they are in my storage unit, and it is 17 degrees outside, so we won't be seeing them soon. If you still need one when it warms up, ask me.

[Tone Meister]

Too funny Enzo! I snorted coffee all over my computer monitor and several pages of notes from this amp.

[Enzo]

I always had 87478 in stock, the TL604s were more an issue in my shop, but the first trick we did was replace the reverb 604 with a wire jumper, leaving it always on, but that freed up a 604 for elsewhere.

[The Dude]

This place shows them in stock.

CA3094 [CA3094 | Intergrate Circuit | |] - $4.72 : HB Electronics, TV & Electronic Replacement Parts Supplier Semiconductors IC Capacitors Transformers Lamps @ hbelects.com

[Tone Meister]

Well, guess what? I found a stray 70487478 in my semiconductor parts bin and now have the amp working 100 percent and all buttoned up. The Phase effect sounds pretty awesome with the reverb. Very convincing Purple Rain!

Thanks Dude, Enzo, and G1 and others who helped out.

[The Dude]

That's great news. The parts gods were smiling on you today!

[Tone Meister]

That's great news. The parts gods were smiling on you today!

From this day forward you shall be known as "Dude, King of Understatements."

[Enzo]

great.


If it comes up again, I still have a half dozen original parts.

[Tone Meister]

great.


If it comes up again, I still have a half dozen original parts.

Duly noted and good to know. And I have some LM3080N on the way and would be able to see where they will and won't work. Then Enzo has the original parts as backup.

Took notes on the TL604 pin3 - pin7 jumper workaround also.

[Enzo]

Yes, you want a working TL604 where it does something like change channels, but an alway on reverb is a better solution than a stuck channel if that is where a repair is stuck.