Blown Fuse - Troubleshoot Why

huntro1 · Guest

Hi VTech,
I'll hold off on the oscilloscope purchase for now. Thanks for your insight about scopes. So, this past weekend, here's what I found out. I measured the AC amperage load at the fuse by recording the amount at initial startup and after the unit was on for a minute. The load at startup was 600mA (well above the level of the 315mA fuse) and quickly settled down to 200mA. Then, I turned off the unit and waited a few seconds and started it back up. Now, I read a peak of 400mA and after several seconds, it settled down to 200mA. I repeated this several times to be sure of the readings. So, it looks like the fuse will blow on startup only. Is that a symptom of bad capacitors? The tape deck works, except for the blown fuse. Will the replacement of C1, C2, and C3 capacitors solve this problem? Is there anything else I should check or consider? Thanks for your reply, Robert.

huntro1 · Guest

Hi Vtech,
Over the weekend, I replaced capacitors C1, C2, and C3. I checked the amperage draw on the circuit and found no change: from a cold start it draws 600mA and from a warm restart it draws 400mA. After a second it is on, it then settles down to a consistant 200mA. So, my question today is what else do I need to check? Should I consider replacing capacitor C4? Does this bounce in amperage indicate other capacitors that may be at fault? Do you have any more insight to share about this problem?
Thank you for your reply,
Robert

huntro1 · Guest

I replaced the capacitor at C4 and checked all measurements again only to find no changes. So, do I replace all capacitors to fix this problem? Well, I am now looking for a resettable fuse I can use in this circuit to replace the fuse. I am looking for a working amperage of 200mA and a trip point of 400mA with a working voltage of 60 DC volts. Any comments on this possible solution? Since the jump in amperage only occurs in the first second of time the unit is on, I thought why not try a circuit breaker type device to solve the problem. BTW, I am able to play reels on the RTR and it appears to be working fine. I just want to limit the damage of the spiking amperage flow when the unit is first turned on. Any comments are welcomed. Thanks, Robert.

huntro1 · Guest

Solution Found! I replaced the fuse with a resettable fuse (Littelfuse 60R020). Now, when I startup the RTR tape deck, it works properly without blowing out the fuse. The amerage level is normal and the unit plays tapes normally. I am satisfied with the results and call a close to this thread since no other comments have been submitted.

train123_not logged on · Guest

It sound like your problem is related to the type of fuse you used as a replacement.
All power supplies will spike the current when they first turn on until the filter caps charge up. Cycling off and then on quickly will result in a lower spike current because the caps still hold some of their charge and need less to charge up.
When changing fuses on the AC side of a power supply, use "slow blow" ones and are designed not to blow during the start-up spike. They usually look like a coiled up wire inside.
On the DC side of a supply you are on the other side of the big filter caps and should not see any spikes. Use a "fast blow" fuse, which looks like a single straight wire inside. Here you want it to blow quicker.