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The power supply will not start up for the 35V & 15V rails. The 10V supply comes up. The Vcc & Vdd voltages for the SMPS ic's do not come up, off of the transformer T3. The waveform off T3 that supplies the Vcc/Vdd looks kind of funny as it has a spike in it. I don't know if the VIPer20A ic could be causing this issue. I lifted diodes D15 & D8 and the spikes were not present. Any ideas?
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Well one idea off the top, how about a schematic so we can have some idea what any of that refers to.Education is what you're left with after you have forgotten what you have learned. -
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Look at your schematic.
First, the SMPS is EXTREMELY dangerous to service. I highly recommend an isolation transformer. The mains is rectified directly. Now there are ground symbols on there. Note the incoming mains filter has a couple grounds and all the output voltages have grounds. ALL of those are the triangle shaped symbol marked "AGND". Now look lower left corner, the other ground. The symbol shaped like a garden rake and labelled "PGND". You will see that in various places.
THAT IS NOT A GROUND. it is a common reference, but it is really more like -170VDC. It IS the common for all the switching side circuits, but if you clip a scope ground to there or something, you'll have burnt parts before you can say oops.
The AGND is an honest to god ground. It is the ground of the secondary side - the side that powers the real world. The primary side, the side that switches, is referenced to that -170 "ground." BE CAREFUL.
Now. SMPS are all about protecting themselves, so disconnect the 35 and 15v supplies from the rest of the unit. Do those voltages come up now with no load? My first suspects are a blown power amp, and shorted output devices are triggering the SMPS shutdown. Next we look at all the secondary side rectifiers. The 35v rails seem to have four dual diodes each in parallel. ANy shorted? I don't know for sure but it looks like the 15v rails are just a 7815/7915 running off the 35v feeds, and so are less likely to be the problem, but check, a short to ground could trigger shutdown.
U4 drives switching MOSFETs Q6,7. ANy of those getting hot or shorted? I tend to think not or youd blow fuses, but you never know.Education is what you're left with after you have forgotten what you have learned.Comment
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I have been using one for the unit under test. Is that correct?Originally posted by Enzo View Post
No, they don't. Only the +10V is up.Originally posted by Enzo View Post
No.Originally posted by Enzo View Post
no. But Q3 warms up a bit if you leave it on for 30 minutes or so.Originally posted by Enzo View Post
I was concentrating on the supply voltages for the VIPer IC (U3 on the pcb), and for U4 and U1, because they come off of the section that is working, but I was measuring them relative to AGND/chassis gnd. I measured them relative to PGND and they seem to be in range: 10.2 V for U3, 11.4V for U1 and 12V for U4. I have not found anything shorted on the board at all.
Thanks for the tip about PGND, I was unaware of that. I was just using AGND for my scope ground, when I was probing the board. And thanks for the safety warning!Comment
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Yes, that is what the iso is for. I tell you, I been playing with voltage about 60 years no and I have serious respect for these SMPS.
The Viper is working, because you have the 10v supply.
And this point I;d look up the data sheet on U4 for insight into how it works.
Nothing may be shorted, but we can go the other way too, like below Q7 is R15, could be open. I see three optos, PC2 runs across the 10v. It then controls U4 in some fashion, There is a line from the top of the LED part off to the amp, but I want to assume the LED is lit during operation. But just what it is doing with Q9 to control U4, I don;t know. Hope a data sheet spells it out. In any case, a bad opto could keep us shut down.
PC3 also controls U4. The LED part is down in the +35 rail supply. Something funny there maybe. yes, I am guessing now.Education is what you're left with after you have forgotten what you have learned.Comment
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Hi. Are you getting 15V across ZD4?
What voltage are getting at Cathode of D1?
Check R15.
I'll post more things for you to check later if you like. But, check the above and let us know.Comment
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R15 is a wire, factory installed.Originally posted by Enzo View Post
The LED's in PC1 and PC2 are forward biased. PC2 is controlling the enable EN1, which shuts U4 down when high. It is sitting low when the unit is on.
Without a +35V rail, I think that PC3 is not going to be turned on.
No, it's at 11.3Vdc.Originally posted by diydidi View Post
401VdcOriginally posted by diydidi View Post
See above.Originally posted by diydidi View PostComment
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Assuming it is working. But what if the LED part is OK, but the sensor end is shorted or something.Without a +35V rail, I think that PC3 is not going to be turned on.Education is what you're left with after you have forgotten what you have learned.Comment
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Hello I'm new to the forum... sorry 2b off the thread topic. Just want to say thank you Enzo and a shout out to your knowledge... Regards to hartke ha 3500 relay issue...Comment
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I never did figure out the PSU issue; I ended up replacing the whole PCB with a new one from Samson. The power amp PCB pulled the new supply's rails down. Nothing measured shorted, but I replaced the 2 power amp IC's and it came up ok.Comment
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Here's a video that deals with replacing the surface mount amplifier IC:
https://youtu.be/7ThZIjHSxpgComment
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Got one of these that cuts out on both left and right power amp outputs once it gets over about 5vac output.
Doesn't matter if a load is connected or not.
Does anyone have the part numbers for the two power amp chips and the controller IC?
Thanks.Comment
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I believe they are TDA8954 if I remember correctly.Comment
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