Seduction phono preamp - getting no readings from LEDs [solved]

[photoeclipse]

Hi,

My first post!

I've just completed the soldering and bought a good multimeter and have been testing as per the assembly manual. Everything tests perfect except each of the LED terminals (A3 & B3, A8 & B8). Seems totally weird because everything else is perfect.

I double checked - all the solders seem good and the silver bands are all set in the correct direction.j

Should I ignore this and test it with current running through it?

[Grainger49]

Ok, what reading do you get on the terminals with the LEDs? 

Start with giving resistances as the manual does.

Double and triple check that the LEDs are oriented with the silver stripe toward the center pins of the tube socket.

[Paul Birkeland]

What tests are the LED's failing?

(You couldn't get perfect voltages and not have glowing LED's)

[photoeclipse]

Hi,

Thanks both of you for your replies.

I haven't put power through the unit yet, as I wanted to try to sort out why the LEDs seem to be failing on resistance testing first.

Thing is, I get nothing at all. Even other terminals where I'm supposed to get nothing read 0.2 or something. These LED terminals read like I'm putting the probe into a lettuce. Nothing at all. They are supposed to read 1 m/ohm+.

I double and triple checked the orientation of the white stripe on all the LEDs, and they all point to where they are supposed to according to the manual.

Every other terminal on the Seduction circuit gives me exactly what the manual says it should. It's just that these LED terminals don't give me a thing - and they are securely soldered and oriented the correct way. Very strange.

Maybe I'll just try plugging in (carefully) and do the voltage testing according to the manual. What do you think?

[Paul Joppa]

By the lettuce-like "nothing" I assume you mean they read as infinite resistance, not as zero resistance. (Actually, a lettuce would probably have enough water in its cells to make a readable resistance - I don't have on at hand but I tried sticking the probes in a carrot and got about 270Kohms...)

Anyhow, meters vary a lot in how much voltage there is available to test resistances. LEDs need around 1.5 volts, while other diodes need half that. So it is quite possible that the meter just won't read anything less than infinite resistance. If the meter has a "diode test" setting that might give a result. Or not, again depending on whether the meter designer expected LEDs to be tested.

[photoeclipse]

Thanks a lot Paul,

I bought the meter yesterday - it is a Fluke 114, and doesn't have a diode test. However I still have the el-cheapo meter I couldn't get to work for the other resistance tests. I went out just now and saw that it has a diode test setting - so I tried it not expecting much and, when touched onto the specified terminals, the LEDs lit up! There seemed to be a reading on the meter too, of about 1900 or so?

Anyway, should I assume with the lit LEDs that the cheapo meter is telling me that the LED terminals are OK?

I really appreciate your help with this, and the other guys (gals?).

If this is successful I'm going to have to try it out on various vegetables!

Cheers, Phil

[photoeclipse]

IT WORKS!

I tried testing all the terminals specified to check DC current and it all checked out. Once switched on, the LEDs all glowed reassuringly (well, two didn't until I switched it all off again and pushed the tube in further) and the DC voltages were all spot-on according to the manual.

Then I tried it with vinyl - the Doors first album - and it is MAGIC!

Thanks again everyone so much for all your help.

Cheers and best regards,

Phil

[Grainger49]

Great first album for a Seduction break in and a great first album all around.

I'm glad you got it working.

Which meter did you finally get readings on?  I use a Fluke and have great confidence in them.

[photoeclipse]

Thanks Grainger49 - Yeas, I wanted it to be a very special album for the try-out.

Well I found the Fluke 114 fantastic for all the resistance tests bar the diodes and for all the voltages. The other cheapy I used for the diodes (which worked great for that but totally useless for the other readings) is something called a DT-830B. I think it only cost $12 or something so I guess it was worth that even just to reassure me about the diodes.

Thanks a lot for all your thoughts and help too - I really appreciate it.

Cheers, Phil