Not sure if is the right board for this thread so happy for moderators to move if necessary.
Background - feel free to skip
I acquired a faulty Function Generator (Instek SFG-1013) for a very low price and am hoping, despite my quite basic skills, to repair it. The unit powers up and generates a display of frequencies. The TTL output seems to be functioning also and the set frequency corresponded with the frequency measurement on my oscilloscope. The main output however delivers NO signal at all. On opening the unit I found 2 resistors badly scorched and one of the output transistors was also running very, very hot.
I have been in correspondence with the manufacturer. They agree with my belief that the 2 main transistors in the main output circuit were blown (which the say causes the resistors to run hot). They also think several other general purpose npn transistors are also likely to be damaged and are currently in the process of securing a total of 9 components which they will supply free of charge (very good of them) and asked if I will take a photo of one of the npn transisters to make sure they send the correct items (5 of them the same)
New concern - the point of this thread
I had the unit open today to take the requested photo and thought I would check a few of the diodes in a small cluster in the output path. Using my DMM in the diode mode. Alternating the pos & neg probes on anode & cathode I got a reading in both directions (on a total of 7 diodes - see pic). Typically the diodes read 0.612V (with pos lead on anode and neg lead on cathode) and 2.30V with probes reversed. I had expected to get NO reading when testing with pos probe on the cathode. All diodes have a very similar reading but diodes elsewhere, outside the output path gave me the expected reading (i.e NIL reading when reversing probes). Could I be missing something basic when testing diodes in-circuit like this or is it likely that all 7 diodes could have shorted simultaneously? I haven't even examined the 2 zener's (not sure how to test them) and if all these components (total of 16 to date have gone south, I wonder if zeners and opamps are likely to have blown too
I've attached a photo of the out portion of the pcb . Sorry for the long post.
Background - feel free to skip
I acquired a faulty Function Generator (Instek SFG-1013) for a very low price and am hoping, despite my quite basic skills, to repair it. The unit powers up and generates a display of frequencies. The TTL output seems to be functioning also and the set frequency corresponded with the frequency measurement on my oscilloscope. The main output however delivers NO signal at all. On opening the unit I found 2 resistors badly scorched and one of the output transistors was also running very, very hot.
I have been in correspondence with the manufacturer. They agree with my belief that the 2 main transistors in the main output circuit were blown (which the say causes the resistors to run hot). They also think several other general purpose npn transistors are also likely to be damaged and are currently in the process of securing a total of 9 components which they will supply free of charge (very good of them) and asked if I will take a photo of one of the npn transisters to make sure they send the correct items (5 of them the same)
New concern - the point of this thread
I had the unit open today to take the requested photo and thought I would check a few of the diodes in a small cluster in the output path. Using my DMM in the diode mode. Alternating the pos & neg probes on anode & cathode I got a reading in both directions (on a total of 7 diodes - see pic). Typically the diodes read 0.612V (with pos lead on anode and neg lead on cathode) and 2.30V with probes reversed. I had expected to get NO reading when testing with pos probe on the cathode. All diodes have a very similar reading but diodes elsewhere, outside the output path gave me the expected reading (i.e NIL reading when reversing probes). Could I be missing something basic when testing diodes in-circuit like this or is it likely that all 7 diodes could have shorted simultaneously? I haven't even examined the 2 zener's (not sure how to test them) and if all these components (total of 16 to date have gone south, I wonder if zeners and opamps are likely to have blown too
I've attached a photo of the out portion of the pcb . Sorry for the long post.