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How to troubleshoot the MiniMax ?

post #1 of 54
Thread Starter 
Hi,

I am in the process of finishing my Minimax. I biased my PS (27V), Tubes(13.5V each), and DBs (90 mV). Then I plug my test wires to my source, then plug in my headphones but there is no output... I seriously have no idea what I did wrong here, and I'd like to have some advice on what to do next.

Any help would be appreciated,
Thank you.
post #2 of 54
Take photos of board, I'm guessing you forgot to wire output resistors
post #3 of 54
Thread Starter 
Here (note that the bottom picture is a photomerge of 2 pictures). Tell me if you need any close ups.

Thank You !!



post #4 of 54
When you turn on the amp, the e12 is off, you will not get any sound until it clicks on after 45 seconds. Do you hear the e12 make a clicking noise after 30-45 seconds?
post #5 of 54
Thread Starter 
Thank you for your reply.

I just tried, and unless it's a very subtle click, I can't seem to be able to identify any click at all before/after 45 seconds. What would that mean ?

(the clicking should come from the omron relay G6A-234P ?)
post #6 of 54
Yes, the relay should click (a single soft click after about 45 seconds) indicating that the time has been met. If you are absolutely sure it doesn't click, I guess we know where the problem likely lies.

Do one test though, measure the DC offset on both channels before the relay to make sure you get something reasonable.
post #7 of 54
Thread Starter 
That would be at which test points ?
I guess Ground and input of QM1 ?
post #8 of 54
Thread Starter 
From left to right (jack to potentiometer) , I get

1672mV (left pin), 27V on the center pin and 2.23 V on the right one
post #9 of 54
Quote:
Originally Posted by K5Doom View Post
From left to right (jack to potentiometer) , I get

1672mV (left pin), 27V on the center pin and 2.23 V on the right one
No, No. Measure output offset from Ground to the tabs on the headphone jack. I don't think it matters, though. If you were able to bias everything correctly, then the signal itself is blocked. I suspect FallenAngel is correct and the relay is not firing.

Unfortunately, the most common mistake is installing the BD139 backwards - but yours looks fine. The QM2 looks a little weird, though - is that the MPSA14? It will not work without that transistor - and it's not a normal transistor - it's a Darlington.

Also, it looks like your input wiring on the pot terminal block is hanging by a thread - maybe those are not making good contact?

Be patient ... your biasing measurements look fine ... it has to be something very simple that's wrong. One sure way to check that the issue is with the relay is to connect some jumpers to Ground, and to the leads on RB14L and RB14R, then to your headphone jack or directly to your headphone plug. This will bypass the relay circuit. The tab closest to the hole is ground on the jack, or the long part of the shank on the headphone plug. It doesn't matter which jumpers of RB14L and RB14R you connect to the other two positions - all we want to confirm is whether you have sound.
post #10 of 54
Any results on this?
post #11 of 54
Thread Starter 
I haven't been home for a few days, I am staying at my GF's place for that time. I'll surely post my results as soon as I test it. Thanks tomb
post #12 of 54
Thread Starter 
Good news, I got sound by bypassing the Relay circuit ! At least, I know the rest of the circuit is working.

For the QM2, it was the 1st transistor I soldered and I just didn't push it all the way through, that's why it looks weird. So, what do you think I should do next ? Order new parts for the relay circuit ? De/Resolder them ?

And thanks again to you two !
post #13 of 54
Quote:
Originally Posted by K5Doom View Post
Good news, I got sound by bypassing the Relay circuit ! At least, I know the rest of the circuit is working.

For the QM2, it was the 1st transistor I soldered and I just didn't push it all the way through, that's why it looks weird. So, what do you think I should do next ? Order new parts for the relay circuit ? De/Resolder them ?

And thanks again to you two !
That's great news! It means the only thing wrong is your relay circuit. From your pics, I didn't see anything else suspicious in the relay circuit - except QM2. It looked to me like the resistors were right, the diodes were right, and the capacitors were right.

If QM2 isn't a Darlingtion (MPSA14), the relay will not close. At the same time, if the way you soldered it in there is suspect, then it also won't work. Why not try taking it out first and soldering it in properly? I doubt seriously that anything has happened to it. That might fix everything.
post #14 of 54
Thread Starter 
Actually, the transistor is the Fairchildsemi (the F logo) MPSA14. I'll try to resolder it and see if it fixes it. but can't I just test the continuity on the leads, since it's not pushed all the way down ?
post #15 of 54
Thread Starter 
I just realized that I ordered 2 of them, I'll try to swap it and see if it fixes it. I'll update when it's done.
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