Where can I find Peavey 87478 ICs for a Phasor circuit?

[Justin Thomas]

Enzo,

Off Topic, but are you having issues with double posts, too? It's been doing it to me a few days now... Not that anything YOU say shouldn't be posted twice...

Anyway, sorry, I'll leave now; just wanted to bring it to your attention...

Justin

[Enzo]

yes, it is annoying, and I see it on other posters as well. This happens every few years. tboy has to do something or other to correct it.

[QdB]

more data

Power off, measure resistance from pin 5 to 6 of U12.. WIth rate maxed you should see about 2k or so. WIth rate at minimum, add the value of the pot to that.

The pot is a 1 Mohm.
From pin 5 to 6 with rate maxed: 2.8 kohm
From pin 5 to 6 with rate min'ed: 1.01 mohm

With both ICs removed from their sockets, power up and take those readings. Pins 8 and 4 should have power supply, but to those other voltages go away?

	U11		U12
pin #	Vac	Vdc	Vac	Vdc
1	0	-13.39	0	*-13
2	0	-14.26	0	-14.2
3	0	-13.46	0	-13.47
4-	0	-14.79	0	-14.46
5	1.4	0.00	0.25	-12.95
6	0	-13.4	0	-14.27
7+	0	15.05	0	15.05
8	0	15.05	0	15.05

*U12 pin 1 started at -13Vdc then steadily climbed for minutes, I let it off at around -6 Vdc, as I wasn't sure if it was safe to continue letting it go

[Enzo]

It is save, because there are no ICs in the sockets. What you were seeing was C49 charging through your meter.

I may have led us astray partly, I guess all those negative voltages may be coming up through R75. All those points are ultimately linked to it.

Just for fun, look to the left for R64. The right end should have the same voltage as pin 2 of U11. (Right end as we see on the schematic, I have no idea which way it aims in the amp) Now what voltage is on the far end? Wondering if any drop is across it.

[Enzo]

It is save, because there are no ICs in the sockets. What you were seeing was C49 charging through your meter.

I may have led us astray partly, I guess all those negative voltages may be coming up through R75. All those points are ultimately linked to it.

Just for fun, look to the left for R64. The right end should have the same voltage as pin 2 of U11. (Right end as we see on the schematic, I have no idea which way it aims in the amp) Now what voltage is on the far end? Wondering if any drop is across it.

[QdB]

Just for fun, look to the left for R64. The right end should have the same voltage as pin 2 of U11. (Right end as we see on the schematic, I have no idea which way it aims in the amp) Now what voltage is on the far end? Wondering if any drop is across it.

U11 pin 2 -14.19
near end of r64 -14.19
far end of r64 -14.21
so, a 20mv drop?

[Enzo]

I wanted to see if the voltage was higher or lower on that far end, it is higher. WHich tells me maybe the problem is U6.7.8.9. If one of them has a short to pin 5, it might be pulling this whole line up to -14v.

Pull all four of those and set them aside, noting which way they install. Now with them out are those voltages different at U11,12? And with ICs back in 11 and 12 might the LFO now work?

I am grasping at straws here. Doing this by remote control makes it harder.

[Enzo]

I wanted to see if the voltage was higher or lower on that far end, it is higher. WHich tells me maybe the problem is U6.7.8.9. If one of them has a short to pin 5, it might be pulling this whole line up to -14v.

Pull all four of those and set them aside, noting which way they install. Now with them out are those voltages different at U11,12? And with ICs back in 11 and 12 might the LFO now work?

I am grasping at straws here. Doing this by remote control makes it harder.

[QdB]

back at the phasor again.

Apologies for the late reply. Holidays and all. Merry Christmas, Happy New Year!!

Pull all four of those and set them aside, noting which way they install. Now with them out are those voltages different at U11,12?

I removed U6, U7, U8, U9
*U11 and U12 are also out

the following are the measured voltages, (similar to post #33)

	U11		U12
Pin #	Vac	Vdc	Vac	Vdc
1	0	-13.29	0	-14
2	0.23	-12.77	0.23	-12.77
3	0	-13.36	0	-13.36
4	0	-14.77	0	-14.77
5	2.6	0.00	0.23	-12.77
6	0	-13.31	0.23	-12.78
7	0	15.11	0	15.11
8	0	15.11	0	15.11

And with ICs back in 11 and 12 might the LFO now work?

Afterwards, with those 4 ICs still out, I put U11 and U12 back in and still no LFO.

Just to be sure, it is voltage and not amperage that I should be checking at pin 6 on U12, right? I just want to be certain that I am checking correctly.