SSR02 - whoops connected wrong

[Simon]

Hi

So as a result of a late evening, I connected my SSR02 to replace a 7915 and forgot to check that of course the pinouts for the 79xx is different to the 78xx.

Result was a lot of smoke from Q3... I have replaced Q3 and although the reg is working, it is not regulating - V out increases with V in but around 4v less...

What else tends to required to replace when this happens? Voltage across base and emitter of Q3 is 0.78v. N1 voltages are:

Pin 2 = 22.3
Pin 3 = 23.4
Pin 6 = 23.4

Input voltage on board is 24v

I am wondering if I have blown the LM337 or LM329?

thanks

Simon

[peranders]

Is it -23.4 or is it -0.6 V?

[Simon]

Hi

Do you mean pin 3 of the AD825? These voltages are with respect to earth.

[peranders]

All measurements are referred to ground if nothing else is said.

The opamp is most likely broken. The reference may be broken also but you don't have to replace it yet. Q3 may be broken but you can check the transistor with a diode test even if it's soldered. A broken Q3 will have short circuit between collector and emitter.

[Simon]

Hi Per-Anders

Thanks, I will replace the opamp first and then Q3 if it is not fixed and then report back.

I am kicking myself for not checking the pinouts!

[Simon]

Hi

I replaced the opamp with another AD825, and then Q3. For good measure I also replaced Q1 and the LM329 once the previous swap outs had not fixed it

I am still getting 20v out with an input of 24v. The opamp áppears' to be working in that pin 2 = 23.3 and pin 3 = 23.4. Pin 6 is 24v.

Unless this 827 is crook as well? I removed it off a brown dog from a previous project.

[peranders]

What about pin 7 of the opamp?

[Simon]

Sorry about the delayed reply, I have been out of the country. Voltage at pin 7 is 24.17V, appreciate your reply.

I received the opamp boards as well thanks - they are great!

[peranders]

In order to trouble shoot you must have a plan  :-)

Omit the LM337 by short the input-output. Lift the C3 and R2.

Measure rel ground.

Output
VR1
N1, pin 2
N1, pin 3
N1, pin 6
N1, pin 7
Q3, emitter
Across H1 (lit?)
Across DZ1
Q1, base-emitter
Q2, base-emitter

J1, J2, tin blob?

Which parts have you changed?

[Simon]

Ok, I will measure all of those

I have the tin blobs in place, and have replaced the 823, Q3 and the LM329

[Simon]

Measure rel ground, with LM337 shorted input to output

Output
VR1 = (pin2 = 0.1v), pin 3= 23.45v, pin = 24.2v
N1, pin 2 = 23.4v
N1, pin 3 = 23.4v
N1, pin 6 = 23.4v
N1, pin 7 = 24.2v
Q3, emitter = 24.2v
Across H1 (lit?) = 2.04v and it is lit
Across DZ1 = 3.3v
Q1, base-emitter = 0.63v
Q2, base-emitter = 0.53v

J1, J2, tin blob? = yes, tin blob

Replaced the opamp, the LM317 and Q3

Which parts have you changed?

[peranders]

Pin 7 should have 0 V and pin 4 -15V to -24 V. Have you lifted the R2 and the C3?

[Simon]

Um no... what do you mean by 'lifted'- do you want them grounded or shorted or ?

thanks

Simon

[peranders]

Removed so the LM337 is bypassed completely

[Simon]

I just applied the -ve supply input direct to the Vout of the LM337 - I thought that this would have adequately bypassed the LM337