[train123_not logged on]

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.

[huntro1]

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.

[huntro1]

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]

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]

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.

[vtech]

[huntro1]

Hi Vtech,
Thanks for your reply. I will get the amp measurement this weekend and post it here. I don't have a scope and I don't know anyone who has one. But, I know where I can buy an old one (1950's model) for cheap (less than $100). What do you think of the EICO 460? Does it have the features I need to do basic testing on audio equipment? What basic features should I be looking for in a scope? Is 10MHz bandwidth O.K.? How about 1mv/div? There are some scopes on Amazon for around $200 new. Do I need any generators built into the scope? Your recommendation is appreciated. Thanks, Robert.

[vtech]

Instead of a jumper, use your meter set to AC amps. What do you measure when you turn the unit on?
The idea is to determine how much current is going thru the fuse. (remember any measurement before diodes G1 & G2 are in AC). There is no need to measure AC across caps since you are dealing with DC at that point.
Your DC readings across C1.C2,C3 are a bit high, so it is possible that you are still dealing with dried up capacitors C2 & C3. Either way, measure the AC amp draw in place of fuse. Do you have access to a scope?

[huntro1]

Vtech,
Over this last weekend, I replaced the capacitor C2 and tried to play a tape by jumping the fuse again. This time it worked and I could hear music from the tape through the headphones! So, I put in another fuse and turned it back on. Well, in one second the fuse was blown again. So, I guess there is still a problem, but what should I test next? Can anyone give me some clues? I think an electronic component is failing, but not completely gone yet. What to do?
Thanks for your reply,
Robert

[huntro1]

Hi vtech,
Over the weekend, I made some more measurements for your review and comment. First I measured C1, C2, and C3 without having a jumper across the blown fuse and the power on. I got: C1 0.5VDC and VAC, C2 0.1VDC and VAC, C3 0.5VDC and VAC. I measured both A/C and D/C voltages because I wasn't sure which to use. Now the interesting part. I put a jumper across the blown fuse with the power on, here's what I found:
C1: 31VAC and 21VDC
C2: 21VAC and 21VDC
C3: 50VAC and 35VDC
After that, I made some additional measurements of the transistors: T203 11.5VDC, T103 12VDC, T102 1.5VDC, T101 6VDC, T4 0.0VDC (erase circuit off), and capacitor C4 33 VDC.
In further examination of the capacitors (C1, C2, C3), I discovered that C2 looks slightly discolored and the clear plastic shrink wrap around it was black at the bottom and not tightly wrapped like the other two capacitors. It also looked slightly bulged at one end. What is the function of these capacitors? Filters?
So, what are your thoughts on the source of the blown fuse? What is the next step I should take in repairing the problem? Your comments are appreciated.
Thanks,
Robert