HH D R18 and R23 - calibration question

[ManBearPig]

Hi Guys, I've searched for an answer for this within the forum but it doesn't appear that anyone else has made this silly error (in case anyone's wondering, don't try to persevere with your build with a screaming toddler grabbing at things in your study - makes for a distracting work environment! wait till they go to bed). I had to replace R18 and R23 due to a mistake (ie, fitted the wrong pots and didn't realise till other components fitted). So, long story short, i need to recalibrate R18 and R23 now, but all the other components are now in. I would rather not de-solder if i can avoid it just due to my iron being too hot on it's lowest setting and tends to damage pads when desoldering, replacing pots was dicey lol. I want a new iron but $$ is tight. Does anybody know how (or if it's even possible) to recalibrate R18 and R23 on a completed board without desoldering? I don't have a scope yet, missus is getting one for my birthday in little less than a month, but that doesn't help me now obviously!

I know is a stupid mistake so any help would be appreciated greatly!!

Oh, It's a HHvd and a standard VCO build.
Cheers everyone

Tom

[ManBearPig]

Hi All, Thanks to everyone that has had a look at my problem, based on the number of views vs replies, i'm thinking it can't be done without desoldering. Thats ok, If i have to desolder i will, just would rather not. So i'm ordering a new iron with digital temp settings, and a scope today (though being good fri, might take a few days). Assuming desoldering certain components is the only option, does anyone know which components i need to remove? (as apposed to everything in the last few steps) i'm getting to the point where i'll do whatever it takes, even removing all components in the last few steps if need be (back to where the calibration of R18 and R23 is done) and if i cook it then i'll rebuild from the start with a new board (It's not much good to me in it's current state, so it's not gonna make things much worse!)

If anyone can tell me which components to remove so i don't have to remove the last few steps worth of components, i'd be enormously grateful

Hope everyone has a nice easter break!

Tom

[6666]

What document or instructions are you working from ?

[ManBearPig]

Hi 6666,

Thanks for your reply

I'm using Revision 1.5 - 21 July 2006 document (it was the most recent i was able to find)

Cheers mate

Tom

[6666]

I dont like trying to do repairs by remote control, but after a quick look I think it can be done without desoldering, if you want to try it.

[kt315]

I don't have a scope yet

it's a problem. you need o-scope for that you ask.

[ManBearPig]

Hi 6666,

Yeah, i'll give it a shot, if it doesn't work i'll desolder gotta go do family easter thing (only about an hr or so i hope) so if i don't reply straight away, i won't be far off. Thankyou for helping me with this, i really appreciate it!

Hi kt315,

Definitely a problem, so many times during this build i've thought that. Should have one next week hopefully. It certainly seems that not having one is a big hinderance!

Cheers guys

[6666]

I think this will work, I have not tried it, I hope there are no mistakes, however I need you to understand that I take no responsibility for this procedure, you do so at your own risk.



Power off

Assuming there are NO faults on board, and using ESD precautions,

Remove IC5 (555)
Remove ic11/12 (74hc221)
Remove ic8(tl072)

With ic5 and ic11/12 removed that should stop all the pulsing and Q9/Q8 should be off.
And when the board is powered there should be +5v on tp7 and tp6 to turn 4066 gates on.

Short pad 1 of ic8 to ground, (see PDF doco).

Power up, stand back and wait for smoke to clear.

The 7660 should be running just check you have + and – 5 volts,
And +5v on tp7 and tp6

Adjust voltage at tp4 to max with R18 (100K)

Measure voltage ACROSS pins 2/3 of ic8, adjust R23 (100 ohms) until zero

readjust R18 so voltage at tp4 is zero

Power off

REMOVE SHORT

Apply oxygen and revive patient , good luck.

[ManBearPig]

Absolutely mate, is totally on me as far as responsibility for the outcome (obviously though, if it works, then full credit to you cos i'm stuck as to how to fix & i doubt i could've figured this one out myself, i'm still learning)

Thats awesome, thanks heaps for that, will try it as soon as i can get a moment (is a little crazy round here today, don't want interruptions while i do this). Will definitely do this afternoon when a bit quieter.

I'll let you know how it goes first chance i get, Thanks again mate Fingers crossed!

[6666]

No drama
hope it works cheers

[Silver Dollar]

I need to do this too. I built the HH then realized you need to trim things as you go.
I just used fixed resistors for R23 as I didn't have a 100 ohm pot and figured I'd just
center the pot before I installed it. I left the offset trims out most chips these days
don't really need that...

I haven't powered mine up yet, waiting for Easter (Hmm better get to that soon...).

[ManBearPig]

Hey all, finally got my little guy to bed & missus watching TV, so time to get busy with this (been trying to get an hour all day but was impossible). So, i'm stocked up with iced coffee and im setting up in kitchen (no carpet and better light). Should have an outcome soon. Will post back soon with results...

Hey Silver Dollar,
Didn't you just kick yourself when you realised? i was so annoyed with myself lol, so if this works i'll be one happy dude! oh, & i have powered mine up, doesn't do much, frequency changes when turning pot, and other pots change tone but no detection. i thought i started to hear some verrry slight change with gold ring (18ct) but it was late and i might've been imagining it!

[ManBearPig]

Hi 6666 and everyone,
Ok, everything went fine as far as no smoke so thats good got all voltages expected until i got to TP4 which seems to just sit at +4.31 to +4.32 throughout the range of R18. Just to confirm, I have multimeter black lead on positive ground and red lead on TP4, starting to wonder if i'm putting black lead in the wrong place? Checked R18 to make sure all ok, smoothe resistance readings from zero k to 100k. Will check all other pots in the morning, getting tired now. Did remove IC9 too, as per the documentation, however i'm wondering now if that should've stayed. Anyway, nothing let out the magic smoke and other voltages were good so it's a start!

[Carl-NC]

I apologize for being late to the party but I just noticed this thread. You should be able to do post-assembly trimming as follows:

1. Remove the short between L1 & L2 (next to TP2 on the PCB)
2. Temporarily short R14
3. Center R23
4. Trim R18 until TP4 is around 1V to 2V
5. Trim R23 until TP5 ~ 0V
6. Trim R18 until TP4 ~ 0V
7. Unshort R14, replace the other short

I think this will work, but I have not tried it.

To answer your other question, if in doubt put the black lead on IC6-pin3.

[ManBearPig]

Hi Carl,

Thankyou for that, I'll try it as soon as i get a chance (will be today, just gotta wait till i got some quiet). Quick question though, should i do this with the components removed (ic5, ic11, ic12, ic8 and jumper from pad 1 of IC8 to ground) or should i put them back in first? sorry if this seems a silly question, would rather ask though than just assume (tends to get me in trouble!)

Cheers,

Tom