Laney hair puller

[Enzo]

I have a Laney L30R series 2 combo here. It is ours. It came in once with little output, and customer declined the estimate. I had putzed with it off and on for a while. I was trying to use my L30R schematic, but it was clearly different. It does not SAY series 2 on it, but when I saw that schematic I knew I was there. Well I traced the signal over and over. It got to one stage and quit. Super low gain there. Pull dirt channel worked, though also reduced.

This amp uses a CMOS 4069 IC as amplifier stages. The CMOS logic is pretty much a little push-pull stage inside. I swapped out the IC, no help. I put the thing aside for better projects. I would get it out now and then, screw around and stuff it back under the bench.

Now that I am clearing my shop, and some friends are going to the Sweetwater gear fest next week, I thought I'd warm this thing up again. Hell, I am a smart guy, I OUGHT to be able to fix this simple freaking amp. I found myself sure enough right back at that IC. Signal comes into it through a resistor, resistor checks out, signal at one end but almost noen at the other, the end entering the IC.

I for some reason measured the resistance input to output of a couple CMOS gates in the IC. I measured that one as like 2000 ohms instead of mega. Maybe I better change the IC again. So I pulled it, decided to check the pads after the IC measured megaohms off the board. Sure enough, pins 1 and 2 were 2000 ohms apart. There is a feedback style gain control across those pins, schematic says 1 meg. Nope, turn it for about 0-2000 ohms.

So I did something I obviously had not done, I LOOKED at the pot, which had clearly printed on it 2.2k. Duh... it was a pull switch pot, as was the mids control. The schematic says mids control is 2.2k. And sure enough, there was my 1 meg pot in the mids position. The two pull switch pots had swapped places.

Well I hadn't done that. Cheeses K Ryst, I been tussling with this amp for several years in my off time, only to find it could never have worked.

Swap the pots, clean the controls, put the IC back in, sounds great. probably be lucky to get $50 for it.

Great, sell it, get the damned thing out of here. I am not sure if I ought to be mad at Laney or at myself. Prolly both.

[Tone Meister]

The evidence I've been looking for: Enzo is human after all. I never fail to learn something when you post, never. And I have solved a legion of problems by doing a simple forum search and considering the advice you provide for a given set of problems. You have NO idea how many new threads your posts have prevented.

This one is no exception, the lesson here being check everything.

[Jazz P Bass]

My hat is off to you big guy.

Best to keep in mind Gibb's Rule #3: Don't believe what you're told. Double check.

[defaced]

Ha! It's always the small stuff.
Reminds me of my boss's favorite troubleshooting tip:
"You can see alot by looking".

[drewl]

Never assume or take something for granted.

Repairing new production failures throughout my career has taught me to always look for production mistakes.

Always great to post them here to help someone else in the future.

[g1]

Nice example of something never being returned for warranty repair. Could never have worked right. Mfgr's don't have to worry about % of failures, just % of actual warranty claims. It's all a numbers game.
And a nice example of perseverance paying off. Maybe not in a financial sense, but those kind of victories can be very satisfying anyway. Congrats.

[Enzo]

Tone Meister, I tell ya, I like to point out my dumb moves. I figure all the pontificating I do around here, people need to know it happens to the best of us. I do make mistakes. I think it happened once about 1976 too. And of course 29 years ago, when I met my wife. And even mistakes and mis steps are informative.

[gbono]

Sell it on ePay or reverb.com with the story above (its all about the story) - probably get more than $50

[Jazz P Bass]

Hmmm. I seem to remember a story about soldering on the plug wires & forgetting the screw on cap.

[mort]

I've been doing hvac work since the 90s and it has always been true that whether you've been at it for 1 year or for a whole lifetime, anyone can overlook something simple.

[drewl]

Sometimes all you need is for someone else to look at something with fresh eyes or a different perspective and they see the problem right away.

Then there was the time in the late '80's where the solution to a vertical amp problem on a Tektronnix scope came to me in a dream.
The solution was right in front of me, but I couldn't see it until I went to sleep and BAM!
My mind saw the problem when I didn't.

[Enzo]

I used to work on pinball machines, back before they all went digital. Each machine was chock full of relays. Each relay had 4-5-6-7-8 sets of contact blades, they were all open frame relays. There were also stepping units with rotating contacts. The boss would go around to all the locations making collections and also noting machines not working. Inevitably he would walk into the shop and announce so and so machine was not working, and "I am sure it is just a contact". Yes of course, one of the hundreds of relay contacts inside had a problem. Thanks for the tip.

[DrGonz78]

Yeah there is this one guy I would buy broken guitar amps from so I could fix and sell them. Every single time he would drop off the amp and simply say "it's probably just a bad resistor." That always tickled my funny bone and never once was it a bad resistor, go figure. Then again quite a few resistors in there so it wasn't completely a bad bet!

[Drewline]

Every time my boss takes in something, he tells us it has to be a loose wire or switch.

[52 Bill]

So, sometimes we need to look for Zebras.

The hardest repairs are the ones that are caused by the unexpected problem. When we start troubleshooting an amp, we all assume that it once was in working condition. At least I do.

A friend brought me a PAIA theremin to fix that he bought used, on-line. Seller said that it was once working, but now didn't. You know the story, blah, blah...

I read through the assembly manual, read the trouble shooting and alignment guides at the website, but could not get it to align properly. So, started checking for bad solder, bad transistors, etc. Nothing. So, i put it aside for week and then went back to try a final time before I suggested that it be sent to the factory for repair.

I decided to clean up some of the wiring to the pots and there it was. The wiper of one of the pots was not connected to anything. Never was. If this thing was ever working, it had to be marginal at best. Much more likely that it never worked. I connected the wiper and it aligned right up just like the video instructions.