AU-717 2663 voltage question

[HDJR808]

I'm hoping someone can point me toward the source of what I am assuming are incorrect voltage readings coming out of my power/protection board. I just completed recapping this board, removing the glue, replacing the resistors that were rotted by the glue, installing a new relay, new D608, TR603, and diodes ZD01 and 02 and D17 and 18. The board is back in the chassis, and the output readings are:

Pins 17-20: 55.7(+/-)
Pins 21-22: 37.3
Pins 23-26: 18.7

From what I can glean from manual and what I've read in other postings in this forum, these readings (particularly the 55.7!) are not even in the ballpark. Any thoughts on where things are going awry?

TIA- Herb

[MarkMeyer]

F-2720 & F-2723 boards; did you replace all 8 (4 on each board) of the Fusible Resistors? (Replace them with metal film resistors, not fusibles.)

If not, look no further elsewhere until you have done so.

[BK201]

There are a total of 12 fusing resistors in the 717, ALL of them should be replaced before you do anything else.

F-2721 and F-2722 (amp boards)
R23 - 150 ohm
R25 - 150 ohm

F-2720 - 82 ohms each
R37
R38
R39
R40

F-2723 - 82 ohms each
R47
R48
R49
R50

All fusing resistors are 1/2 watt metal oxide

these all measured several million ohms each when I went over my "dead" 717

[Hyperion]

Sorry to hear you are having problems with your AU717 - 2663 - Power Protector Board, here is what the voltage readings should be

According to the schematic
18 & 20 = 33v
24 & 26 = -33v
17 & 19 = 33v
23 & 25 = -33v

All of mine are around 32v which is normal.

Pins 17-20: 55.7(+/-) voltage far too high looks like the +ve regulators are wide open
Pins 21-22: 37.3 ?
Pins 23-26: 18.7 this voltage is far too low (also hope this is -18.7v !).

I assume all these checks are with respect to ground ? (pins 21 & 22)

I would check the polarity of all the components you have replaced and check for bridged tracks/dry joints as well. Not sure about the reference to pin22/pin21 at 37.3v, both are ground pins, perhaps this is a typo, in any case you need to get the PSU output voltages correct first.

I hope you have disconnected the power supply from the rest of the amp as with voltages like this you could damage more components in the earlier stages of the Amp.

Check the voltage at the positive ends of ZD01 and ZD02, this should read the zener voltage or about +13v – this is the key to getting the regulator to work, check this and report back.

Also Mark M, et al are correct to direct you to the fusable resistors on Equalizer, Tone Control and Driver Boards, very often a source of problems - but not the one you specify IMO.

John

[HDJR808]

Thanks for the responses. I will dig into this again this weekend.

The PSU board is the only one back in the chassis, so I'm not feeding these voltages to the other boards, and I'll check that my pins 21/22 readings aren't mistaken.

Also, I have replaced all of the fuse resistors on the boards mentioned while they have been out to recap them. This forum is invaluable in guidance for the trouble spots in these amps, and I have tried to incorporate all of the info I have found as I have refurbished this unit.

Thanks- Herb

[HDJR808]

Okay, back into my f2663 mess, and still unable to makes any sense of the readings that I'm getting. And please forgive my ignorance, but I have only a bare understanding of what I'm working with.

The first readings I got were after I had installed the board back into the chassis, with all other boards still out and just the connections in and out of the 2663 board. These were the voltages in my original post: too high, too low, and voltage at the ground pins.

I've pulled the board again, and checked the polarity on all of the caps and diodes that I replaced, and checked for shorts in the traces. Everything appears correct. I then hooked the board up to a variac and fed it the same 41 volts that was the output of the transformers, with the same voltage results as before.

In regard to the suggestions from Hyperion, I checked the voltages at ZD01 and 02, which are reading at 36V, far higher than the 13V he has indicated.

I am getting close to the schematic voltages (51,-51) at R06 (55v) and R16 (-55v).

I'll dig back in and see if anything else is obviousl to me, but I wanted to post what I've found so far and see if any one had any suggestions.

This board is from the amp that I originally bought in 1978, but I have 2 other 717's, and am about to pull the the working, recently recapped 2663 board from one of them to compare readings with. I am getting the correct voltages on pins 17-26 on that board, but I don't want to try fishing around on an energized board in the chassis. It is way too tight in there.

I have found that unsoldering the 20 or so wires to remove this board is actually easier while it is still mounted in the chassis and then it can be slipped out without dropping the entire board/cap assembly out. Soldering and de-soldering those friction pins seems easier when the board is still firmly mounted.

Thanks again for everyone's suggestions. I have recapped all of the other boards in this unit, and replaced all of the fuse resistors as everyone has recommended.

I am also nearing success in motorizing the volume pot for this amp, and will post all of the details when I am done. It is a bit of a Rube Goldberg fabrication, but will be entirely internal.

Thanks for any help- Herb

[HDJR808]

Okay, thanks for bearing with me.

Just pulled the 2663 board from the other amp. Checked the voltages first- seem to be correct. Hooked it up to the variac, hot to pins 1,2,5,6 and neutral to pin points 13,14.

Now I am getting the same oddball readings as the other board, so I'm guessing that this board must be fully connected to all of the other boards to function properly. Or I've wired it wrong.

Please feel free to tell me that I'm a moron and completely off track, because I really do only partially understand what I'm dealing with. But it would be good to learn, and hopefully get this thing back together and working.

Thanks- Herb

[EchoWars]

Unless the regulator is connected to the driver boards, you will not read the proper voltages out of it. I forget why, but I think one (or both) of the regulators gets its ground reference from there.

[HDJR808]

Thanks Echowars- I'll start re-assembly tomorrow and see if things start making sense. What do you think the chances are that I've caused damage by energizing the board without the proper connections?

Thanks-Herb

[EchoWars]

If my previous post is correct, none at all...the regulator would simply be floating with no ground reference so the voltages would be off.

I've powered up the regulator on 717's lots of times to check voltages, only to read numbers that were totally screwed before remembering that, without the drivers installed, that's to be expected.

[HDJR808]

Well, that seems to be the case with me. Too bad too, since it would be nice to check readings while the board is on the bench.

Thanks- Herb