vintage 1176 restoration PICS!

[soundguy]

Installed new 1N4003 diodes. Still cant get a DC reading. Using 2200uf caps for c23-26, polarity is right and they test for continuity where they should.

get the following AC readings using the PT from a reissue 1176, does this mean anything to anyone?

CR6 20.6v/8.7v
CR7 23v/8.6v
CR5 1.2v/20.6v
cr4 1.2v/23v

cr28 1.2v

cr9 1.2v

R80 has 1.2v ac across it.

no bulbs connected.

r81 and r82 are 1K.

what else is gonna effect the power supply.

dave

 

[Svart]

i can't find those part numbers on Amveco's site..?? those colors seem strange to me.. I've used almost nothing but Amveco trafos for my many PSUs..

 

[soundguy]

sorry, they are avel lingbergs not amvecos...

the PCB is single trace with soldermask, no ground plane. The holes for the diodes were enlarged with a drill and one of the tracks to one of the filter caps has a drill hole in it as well. I cant find any shorts with a multimeter and am getting continuity where I am supposed to be getting continuity. Could this however be part of the problem? Doesnt seem likely, but Im pulling at the short straws now...

dave

 

[Svart]

looking at the trafo wiring, I assume you are looking for 110v in and 30v out?
I noticed some that might mean nothing but I'll mention it anyway:


"secondary is black 0V red 25V and Orange 0V yellow 25V"

I think it's supposed to be black/orange 25v red/yellow 0v??

like this:

Primary:
gry/brn line
blu/vio neutral

Secondary:
Blk/Org +V
Red/Yel 0V(ground)


I think i remember reading that toroids wired backwards can cause strange things to happen. but then again i could be wrong.. or drunk. :guinness:

 

[soundguy]

well, at this point Im using the transformer out of a working 1176 and the problem is clearly on the PCB, I'll worry about how to properly hook up the torroid after I figure out wtf is going on with the power supply. Anything that takes this long to figure out has to be amazingly simple to fix.

dave

 

[Svart]

you get AC readings but no DC readings? Not sure what your numbers divided by the / means

have you tried removing the Vreg and measuring?

 

[soundguy]

thats correct, no DC readings...

just measured both sides of the diodes in circuit to ground. I havent removed the zener but cant see how that would be the problem, I'll try that.

dave

 

[SSLtech]

[quote author="soundguy"] I havent removed the zener but cant see how that would be the problem, I'll try that.[/quote]
A shorted (or wacky) Zener would ruin your day for you.

However, the zener is fed with a resistor. The junction of the caps, the rectifier diodes and the resistor should have ripply but close to full value DC on them even with a hard short at the Zener. A scope would point you right to where it all goes pear shaped...

Keith

 

[soundguy]

I replaced both zeners and got the same thing.

am I retarded? I have two other working 1176's on the bench next to this for comparison, I promise Im not insane.

Before I remove the zener and turn the thing on, do I stand to damage any other components by powering up like that?

the 36v zener I removed measures .591 V on my meter. others out of the bag test similarly. Im assuming its good, I tried it in another 1176 and it worked fine before I installed it in the screwy unit.

dave

 

[soundguy]

man, have I stumped everyone here?

dave

 

[Mark Burnley]

Hi Dave,

Been away a few days...what's happened!?!?

Where are you up to now- those voltage readings on the toroids sound strange. Let me know what's going on...

Mark

 

[Mark Burnley]

I just re-read the last few pages...

With your toroids, you mentioned a few measurements you've made. What meter did you use? Check your batteries- dying batteries can give bizarre results.

You need to check that your secondaries are correct- disconnect the transformer entirely, and check both secondaries for continuity. It's possible that the datasheet is wrong...sounds ridiculous but it has happened.

Did you take the secondary measurements with the transformer disconnected from the circuit? Try 115Vac>toroid and measure the secondary voltages with the secondaries not connected together.

Don't forget that toroids have a very high leakage capacitance, and unloaded you can read very high AC voltages- a high-impedance DMM will measure this.

We'll get it sorted.

Mark

 

[Svart]

i feel stumped! I'm not sure how you can't be getting any kind of DC through the diodes.. that's just strange. are they getting hot? the next thing to do would be to remove all resisters on the output side of the psu to see if anything in the circuit is dragging it down.. however you should being seeing hot diodes and PSU trafo if that were the case.. It almost sounds like the trafo is ac coupled to the board but not DC coupled.. are the wire leads covered in epoxy/wax/plastic to keep them from corroding? the power toroids we use at work are covered in that stuff and sometimes the assemblers fail to scrape it off and get strange voltages almost like you are seeing.

just a thought.

good luck!

 

[soundguy]

ok, I have a fluke 8060a with brand new batteries, was able to duplicate everything. I checked the secondaries on the power transformer and they test right. The meter had a hard time with the 4 disconnected secondary leads, but was able to measure .326v AC. With black/orange connected I get 83.6V, red 56V, yellow 56V. Connected to the circuit I get no DC readings at all and basically 55V / 35V and 64/36V on both sides of the diodes. The power transformer isnt getting hot. The diodes arent getting hot. The power transformer leads dont have any waxy coating or anything like that.

For now its not even worth getting into the power transformer as I took the power transformer from a known working 1176, hooked it up and got the same behaviour, so its something on the board. what in the F on the PCB could be causing AC coupling and no DC rectification. Ive replaced ALL the diodes and get the same thing. Maybe drilling the PCB has shorted something, the diode holes were drilled to accomodate thicker leads, however I cant find any shorts with my meter and everythign tests good for continuity. It seems like even if something was totally screwed up in the circuit the diodes would at least pass DC for a second, I put new ones in and fired it up with the lead on the diode and got no reading. I am completely stumped.

Also, its not the power wiring in the box either, I just unhooked the leads from a working 1176 and flew them out to this board, so its doing it through the power wiring from a working 1176 as well.

damn. this sucks.

dave

 

[Svart]

black/org connected? the centertap would be red/org with black and yellow feeding the diodes.

 

[edanderson]

is the centertap of your transformer connected to 0v on the board?

is 0v on the board connected to the chassis ground?

is the chassis ground connected to the mains ground?

ed

 

[soundguy]

ok so I just wanted to let all you guys know Im a total retard.

more on this later.

there is now DC and a big party.

dave

 

[Svart]

do tell.....

 

[soundguy]

ok well, there's this pad labeled GROUND. Its pretty important to hook that up. Im such a retard...

Anyway, got the unit working, stuffed 2n3391a's in place of all the 3707's just because I didnt have any and dont feel like waiting for an order to ship from mouser.

I got the line amp working, it sounds great and is much cleaner sounding with the black gate caps.

It's not compressing at all and the meter sits dead in compression mode. I suspect I didnt wire a switch correctly, Im going to go through and check all the voltages against the working unit I have open now.

dave

 

[Svart]

:thumb:

damn the grounds! :green: