Help troubleshooting CTH build

[arteom]

holland,

with resitors is a visual inspection enough or how would I go testing them with the DMM? Also, would it be the same values that I would be looking for on all transistors (.7v)?

thanks

 

[holland]

Use a DMM, it should be fairly quick to do. There's 3 resistors. Each of them will be different values. 1K, 9.31K and 6.98K. Set the DMM for ohm, and set the range to auto or just high enough to cover the resistor value. The DMM will measure the resistance and it should be ~1K, ~9.31K and ~6.98K.

The values on the transistors, yes. Just note that PNP is different than NPN. PNP is the opposite of NPN as far as the test goes. The fail case noted for the Q1P and Q2P will be pass for PNP like BC327. Use the letters as a guide. Red to P and Black to N. P-N-P will pass. N-P-N will pass with ~0.7V. Swap the leads and Black to P and Red to N and it should read 0.

Also, note that Q7 will fail one of these tests. Look at the schematic. The base is shorted to the collector by design.

 

[arteom]

thanks for the tips holland, will run through all transistors. One more question though, on some of these I'm getting a difference, on one pin it will be say 6.9v and on the other it will be 5.1v. Is this enough to swap the transistor or is this kind of a difference acceptable?

 

[cfcubed]

Quote:

Originally Posted by holland /img/forum/go_quote.gif Be prepared to have to make multiple orders because you may fix something to find something else down the line is dead. That's just the way it is for DIY life.

Or use the shotgun approach. But as you are starting your DIY journey, you are getting good advice from those here if you want to learn something

It's a good education crawling through & diagnosing what may be bad provided you have the time & patience (& tools, e.g. solder vacuum, desoldering braid).
Shipping & taxes can add up going piecemeal though... If ordering a LM2595 you may have to go Digikey & I'd add anything I think I might need at that time (7824 reg, LV TO92s, see BoM). And watch out frying more things by taking measurements on a live CTH. Take that from me

For now I suppose getting your heater & 24V Low Voltage circuits going is a good 1st step.

 

[holland]

Quote:

Originally Posted by arteom /img/forum/go_quote.gif on one pin it will be say 6.9v and on the other it will be 5.1v. Is this enough to swap the transistor or is this kind of a difference acceptable?

It's hard to say. I would just replace it anyway. It really depends on the accuracy of your DMM and if it can really handle 0.7v +- 0.1v. The real things to look for are also shorts and opens when it shouldn't be. That's a completely blown transistor.

Quote:

Originally Posted by cfcubed /img/forum/go_quote.gif Or use the shotgun approach.

That works, we haven't even gotten to the e12.

It's kind of hard to see what the problem is there without power.

I suppose we could use a 24V linear regulated wallwart, if you have that available and feed that directly into the 24V line and remove the 24V reg.

Do definitely double check the LED itself and the wiring of the LED against this diagram.

 

[arteom]

Well I'm crossing my fingers on the E12, on first powerup it seemed to be acting accordingly, the LED was red for about 15 seconds then went green. I measured from SG to OG and got the right reading, also measured OL and OR from SG and all seemed good. I did not get correct readings from two resistors (R1H and R2H), so am guessing those went bad, and looking back that probably played a big role in the heater not working.

Had I not gone back and messed with it. I did learn allot though, some things the hard way and some things about troubleshooting problems.

I placed orders on digi key and mouser, luckily digi-key only charges about $2.00 for such small orders to be shipped by USPS first class mail. Should have parts in a few days.

Thanks for all the help guys, I would not have had the courage to go ahead with this was it not for the helpful and knowledgeable community here at head-fi. Will report back after the parts are replaced.

 

[arteom]

Hey guys, I got something odd going on here. On Resistor R1H I'm getting a value of 1.4k, and sometime up to 7k (it will start at 3k and and go up to 7k), this is due to a faulty ICH right? I got the replacement parts, and replaced that particular resistor, but even with the power off as soon as it was mounted to the board it gave wrong readings. The other resistors in that area give correct readouts, and the same resistor out of the board gives a correct reading. I have also pulled out Q1P, Q2P and the ICP, plan to replace those as soon as I get this resistor reading right. Might need to replace Q4L and Q4R, but I will replace all above and see if the condition of the unit improves, if not I will go ahead with those two as well.

Thanks!

 

[zkool448]

Quote:

Originally Posted by arteom /img/forum/go_quote.gif On Resistor R1H I'm getting a value of 1.4k, and sometime up to 7k (it will start at 3k and and go up to 7k),

Not sure if this helps, I can't troubleshoot circuits sadly due to lack of electronics skills but I only measure a resistor's value when it's off the board.

If you measure their value while soldered onto the pcb, it could be connected in parallel with other resistors/caps on the same circuit hence a good chance you'll get wrong impedance readings. If not mistaken, R1H and R3H (and C4H?) I think are all connected in parallel when the heater is switched to 6.3v.

 

[arteom]

Oh, right

. Well I have replaced the ICH, ICP and Q1P and Q2P. At this point I am not getting a green or red light but am getting a reading from SG to OG of 12v. On the tube socket pins I am getting the following readings: pin1 - 103.8v, pin4 - 0v, pin5 - 0v, pin6 - 103.9v

Any tips on what I should check next? I might tomorrow go on to replace Q4L and Q4R, I had a hard time replacing the previous parts as there was solder still in the holes of the faulty parts, the transistors and bothe ICH and ICR while are making contact they are not mounted low to the board (both Q1P and Q2P are standing pretty tall on the board, although I don't think it should be a problem for those two). I think with the ICR I might be bale to get it a bit lower. For Q4R & Q4L I think I might have to trim the leads a bit before mounting.

 

[adamus]

is that with opamps in? The servo isnt doing anything by the look of it.

When i remove components i normally put a blob of fresh solder on the hole, then use a solder sucker to clean the hole out, looks as good as new then.

 

[arteom]

Yeah, with opamps in. Not exactly sure what part the servo would be. Thanks for the tip with the fresh solder, I am really new to the hobby and can use all the small tips I can get. I use a desoldering bulb btw, anything else that might be better for the job?

 

[adamus]

I use a spring loaded sucker, but a bulb should be fine. The fresh solder helps to transfer the heat to the old stuff in the hole.

and you will definately need some 'helping hands' to do it properly.

The servo can be seen here

http://www.cavalliaudio.com/cth/main...cs/ipschematic.

However..... you shouldnt need the servo to work to get the e12 clicking with the tube removed.

whats the 24v rail measuring?

 

[arteom]

How would I go about measuring the rails? Sorry I am really new to this and still trying to get my head around the workings of this.

 

[adamus]

black probe on SG, then red probe the output pin of the 24v regulator (the one with three legs) make sure you do not short it (ie touch two legs at once, doing that will kill the reg)

or, measure with respect to SG, the opamp legs.
http://www.syntax.com.tw/proddata/IC/IC-TL081.JPG

Any chance you could post pics of top and bottom?

 

[arteom]

Quote:

Originally Posted by adamus /img/forum/go_quote.gif black probe on SG, then red probe the output pin of the 24v regulator (the one with three legs) make sure you do not short it (ie touch two legs at once, doing that will kill the reg) or, measure with respect to SG, the opamp legs. http://www.syntax.com.tw/proddata/IC/IC-TL081.JPG Any chance you could post pics of top and bottom?

I get a reading of 24.1v, is that about where it should be? I don't have access to a camera atm, will take pics tomorrow if needed.