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
Is it -23.4 or is it -0.6 V?
Hi
Do you mean pin 3 of the AD825? These voltages are with respect to earth.
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.
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!
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.
What about pin 7 of the opamp?
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!
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?
Ok, I will measure all of those
I have the tin blobs in place, and have replaced the 823, Q3 and the LM329
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?
Pin 7 should have 0 V and pin 4 -15V to -24 V. Have you lifted the R2 and the C3?
Um no... what do you mean by 'lifted'- do you want them grounded or shorted or ?
thanks
Simon
Removed so the LM337 is bypassed completely
I just applied the -ve supply input direct to the Vout of the LM337 - I thought that this would have adequately bypassed the LM337
Hi Per-Anders, have you had a chance to look at my post? Perhaps if you could send me some reference voltages I can work out what is dead myself.
regards
Simon
I'll suspect the opamp is blown. Have you mounted it correctly.
Yes, I swapped that out and still get the same voltages that I have posted.
I am not keen on giving up, but my DAC has been out of service for a while, so I may have to resort to getting a ready made one from you and then come back to this one later.
If you have the opamp in a socket you could test to remove it. By this you could check your voltage reference.
You wrote in an earlier post that pin 7 had 24 volts where it should be 0 V. Where did you measure really? Pin 7 is connected with copper to the ground so it's impossible to get this value.
Hi,
I will double check this, but the 825 is soldered in and I have replaced it twice already.
In the meantime I will send you an email about buying some more boards and a pre assembled SSR02 - this one may in fact be cursed!
Hi everybody. Had a similar problem like the OP. For SSR02 -15V I measured -7.6V at the output. I see that nobody has solved this problem yet, so I wanted to say what worked for me. After replacing the AD825 it turned out that I misunderstood the meaning of "alternative position" for the voltage reference. I used the "regular position" as indicated on the circuit board, but apparently the voltage reference has to be in the alternative position for -15V. Perhaps Per-Anders would be so kind to confirm this since I do not really understand this part of the circuit. The regulator now works like a charm!
cheers dan
I can make this more clear but if you check the pictures and also the schematics you might realize that I have made one symbol and footprint for LM329 OR LM431. VR1 with fat outline on the pcb is the LM431 and with thin for the LM329.
Thank you Per-Anders. I might be a good example that you cannot make everything "fool proof" :-)...