Repairing Polaroid 600 Flash Board

[Camdawg13]

Hey Everyone,

First time poster here. I work as a camera repairman and know a small amount about electronics, but not enough to really dig deeper than swapping general components on a circuit board. I've had an issue with these Polaroid flash boards for awhile now and I've spent months swapping components from other flash boards to no avail. I did some digging on the internet and found a decent schematic of the board that I'll attach. Ignore the red lines and red components, as those were added on by someone modding their camera.

Now to the problem. The flash capacitor never charges when power is supplied to the camera, as well as the Q1 transistor gets incredibly hot to touch (which they don't normally do). In addition, the iconic whirring noise of the flash capacitor charging has been replaced with a lower pitched, quieter humming noise.

If any of you could take a look at the diagram and recommend where I should troubleshoot that would be fantastic. To give a little insight on how I've attempted to fix the problem, I've tried replacing the flyback inverter transformer, many of the resistors in the path of Q1, as well as transistors that lead to Q1, and obviously Q1 itself.

Feel free to ask more questions, I'll be forever grateful if I can finally get these cameras working again.

-CamDawg

[Gyro]

Welcome,

If Q1 is getting hot but it's still making (distressed) oscillating noises then I suspect that something on the +H output is drawing too much current - maybe the HT reservoir cap, more likely shorted HT rectifier D1, also things like shorted TH1, SCR2, C7 etc. Basically, once you're sure that the HT cap is discharged, probe around the HT side for shorted parts.

Good luck and do please report back.

[GregDunn]

If this is more than a few years old, the likelihood that one of the high voltage electrolytics has begun to degrade is pretty high.  They're subjected to repeated high voltage charge and discharge every time you use the unit.

[Camdawg13]

If this is more than a few years old, the likelihood that one of the high voltage electrolytics has begun to degrade is pretty high.  They're subjected to repeated high voltage charge and discharge every time you use the unit.

Yeah good thought Greg, swapped it though and it didn't seem to be the cure. Same problem.

Welcome,

If Q1 is getting hot but it's still making (distressed) oscillating noises then I suspect that something on the +H output is drawing too much current - maybe the HT reservoir cap, more likely shorted HT rectifier D1, also things like shorted TH1, SCR2, C7 etc. Basically, once you're sure that the HT cap is discharged, probe around the HT side for shorted parts.

Good luck and do please report back.

Gyro, I like your thought. Since I'm not well versed in Electronics, if you have time, think you could explain to me why it would be on the other side of the flash capacitor if the capacitor doesn't even charge? I just don't think I understand. The diagram states that the "bottom" portion of the circuit is "High Voltage Supply." So wouldn't my problem be isolated to the bottom part of the circuit before it gets to the flash cap?

-CamDawg

[Gyro]

Sure.

If you check over the circuit, there are several [Edit, well, 2] points marked ' +H ', these are all connected to the positive pin of the main HT capacitor, it's not just the bottom of the page. The capacitor can only charge if there is current available to charge it - if, for instance TH1 is shorted, then it would take all the output current from the inverter transformer, leaving nothing left to charge the capacitor. D1 would be another prime candidate, if shorted, the transformer would try (and fail) to pump AC into the capacitor.

[Camdawg13]

Sure.

If you check over the circuit, there are several [Edit, well, 2] points marked ' +H ', these are all connected to the positive pin of the main HT capacitor, it's not just the bottom of the page. The capacitor can only charge if there is current available to charge it - if, for instance TH1 is shorted, then it would take all the output current from the inverter transformer, leaving nothing left to charge the capacitor. D1 would be another prime candidate, if shorted, the transformer would try (and fail) to pump AC into the capacitor.

Gyro you are a genius. TH1 solved it. I guess I never thought of the + side of the capacitor. Thank you SO SO Much!

-CamDawg

[Gyro]

Yay, it's nice when one goes so smoothly. You're welcome.

Chris

[In Vacuo Veritas]

If this is more than a few years old, the likelihood that one of the high voltage electrolytics has begun to degrade is pretty high.  They're subjected to repeated high voltage charge and discharge every time you use the unit.

No, it isn't. Could you people PLEASE stop with this "replace all electrolytics on sight for no reason" "advice"?

It's nonsense, as has been shown here once again.