Speedball 1.1 Upgrade - Small Board OA voltage high [resolved]

[adrian.f.hull@boa]

Hi there - I completed my Crack 1.1 several months ago, it has been working perfectly. I took my time with the build and all checks were OK and it worked first time. I have just started the Speedball 1.1 upgrade (which I bought at the same time as the Crack) and have installed the Small Board. On carrying out the voltage checks, they were as follows (I am in the UK, so 240v mains supply):
OA - manual says 60-90v - I got 171v    *** OUT OF RANGE ***
IA - manual says 170-270v - I got 184v
B-A/B - manual says - 0v - I got 0v
IB - manual says 170-270v - I got 184v
OB - manual says 60-90v - I got 70v

I checked through the LHS of the diagnostic flowchart (on p.20) and got to "Are both 9-pin socket LEDs lit?" They were. I checked the 9-pin socket voltages and found them to be as follows:
A2 - 75v
A7 - 80v.
These two solder joints LOOK fine - if they weren't, wouldn't that have upset the basic Crack's functioning? Also, when the flowchart says "Are both 9-pin socket LEDs lit?", I assime that 'lit' means 'OK', whereas 'unlit' means 'NOT OK' but the flowchart link to 'check/re-solder A2/A7' follows the answer 'yes' to these two LEDs working. i.e. suggesting that 'lit' in this case is an error condition.

Maybe it wasn't a good idea, but I checked to see if the amp was still working at this point (without having resoldered A2/A7) and it most definitely was - it sounded great!

SO - am I OK to continue to the Large Board or is there a problem, here?

I would very much appreciate your help. (I did browse the Forum but couldn't spoy this precise situation).

Many thanks,

Adrian Hull.

[Paul Birkeland]

Lit means illuminated, are the LEDs on the 9 pin socket glowing?

Are both halves of the 12AU7 still glowing?

If the answer to both of those questions is yes, often times you just need to reflow the solder joint on the center leg of the MJE350.

[adrian.f.hull@boa]

Hi Paul - thank you for your swift reply.

In answer to your questions:
Yes, both 9-pin socket LEDs are glowing and both halves of the 12AU7 are still glowing. Not very brightly - the larger valve is much brighter - but they are - see pics attached. Also, all four LEDs on the Small Board ARE glowing (tricky to see, but they are).

I re-flowed the solder on the middle legs of the two MJE-350s and this made the A2 and A7 voltage readings now zero.
Q1 - is this correct? (the LHS of the p.20 flowchart implies that a zero voltage IS correct).

However, the five voltage readings on the Small Board are unchanged, with OA still out of +10%  range at 171v.
Q2 - is this a problem that still needs to be resolved?

Please provide explicit answers to Q1 and Q2, please! :-)

Thanks again,

Adrian.

[Paul Birkeland]

Can you post a photo of the bottom side of that small C4S board? 

[Paul Birkeland]

I re-flowed the solder on the middle legs of the two MJE-350s and this made the A2 and A7 voltage readings now zero.
Q1 - is this correct? (the LHS of the p.20 flowchart implies that a zero voltage IS correct).

Yes, around 0V is correct.

However, the five voltage readings on the Small Board are unchanged, with OA still out of +10%  range at 171v.
Q2 - is this a problem that still needs to be resolved?

A Crack with voltages that are 2x as high as they are supposed to be is to be considered not working until these problems are addressed.

[adrian.f.hull@boa]

Hi again - here's the best pic my phone can manage of the underside of the Small Board.

Thanks,

Adrian.

PS. Going to bed shortly (11:00pm) so there will be a transatlantic lull...

[Paul Birkeland]

I think there's either lead free solder here or a cold iron.

When you reflow the solder joint on the middle of the MJE350, hold the hot iron on there for a good five seconds to really let the solder flow out. If you have lead free solder, find some leaded solder!

[adrian.f.hull@boa]

Hi Paul - solder is lead multicore (see pic!). I reflowed the middle pins again - my iron is only 25W, so that may have been an issue. But it didn't change anything. HOWEVER, having a poke around and being careful to check everything in that area, I found that the link between A6 and (small board) OA had become disconnected at OA - it must have slipped out when I soldered the link at 1U to OA!!

So I'm not infallible after all!

The reading at OA on the small board was now 71v. 1A = 191v;  B-A/B = 0v; IB = 191v and OB = 71. Perfect!

I went on to construct and install the large board. I was careful to give the middle pegs on the TIP-50s a good amount of time to flow the solder properly. Resistance readings OA and OB were nice and high, but a bit different: OA was 1.3Mohms and OB was 500kohms. I presume that this is OK. Voltage checks were 13% over your upper limits on OA and OB (large board) but, again, I presume this is OK.

Back on the hi-fi rack, and all is functioning well. It sounds really great (but I'm going to have to forego the A/B test!).

Thank you so much for providing a much-appreciated lifeline. I'm a very happy bunny, now. And my Sennheiser HD800s's never sounded better!

Have a great day.

Adrian.