Yamaha CR-450 help

dneu201

Well-Known Member
I have a Yamaha CR-450 that was fully recapped and worked perfectly for about 4 months while I owned it. I sold it to my aunt to use in her shop and it only lasted 3 months until it started blowing power fuses. When I picked it up to take home and look over, I noticed my cousin had wired some extra outside speakers into it in series. The night it stopped working he had it turned up 3/4 for 3 straight hours.

The issue it has is consistent blown power fuses upon turn on. I checked all solder joints and tested each diode directly after the transformer. Can someone recommend where I should look next?

Thanks!
 
I think your cousin is the problem, other than that I suspect one or all of the output transistors are fried. The best thing is to take it to a local (reliable, reputable) technician to diagnose and have fixed. Most of what's in a CR-450 can be fixed...I don't think there are any "unobtainium" components within. It's a nice little receiver, often sold with a companion Yamaha manual turntable.
 
Lol. I agree my cousin is the problem. I called him an idiot and told him he doesn’t deserve this receiver and gave him an junky insignia to use for the time being. I have experience replacing output transistors so I will unsolder then today and check them to see if any are bad.

Anything else I should check while looking? In the past, when I’ve seen output transistors go it blows the speaker channel fuses and not the power fuse.
 
I just went through and performed a diode test on each output transistor; all 8 of them tested fine. Any idea what I should try next?
 
TR511,512,513 and 514 are the 4 driver transistors. These need to be checked as well.
 
I suggest building a dimbulb tester. -- Will save you some money on fuses.
Then remove fuses F501-504 and then check to see if the bulb dims down. Or..... see if it still blows the mains fuse.
 
Ok. Quick update on this. I’m building a dim bulb tester this weekend, but tried powering on the amp with all the speaker channel fuses pulled out. The amp still blew the power fuse.

Would that help me narrow down that the issue is not in the amp section and probably a power section issue?
 
I just finished building a DBT. What wattage bulb should I use? I have a ton of 60 watts but it seems most people use 100 watt.

Thanks.
 
Try the 60. After first checking D808 bridged rectifier and C808 and 807 main filter capacitors for shorted circuit.
 
Ok. I'm running a test of the bridge rectifier now. Here are my readings:

1. Across the two "AC/Wave" inputs: OL (switched the probes and read .456V)
2. Across the postive output and wave input: 0v (0v after switching the probes)
3. Across the negative output and wave input: OL (.458 after switching the probes)

It looks like the "-" side is good but the "+" side has an open diode. Is there another part I should check? The two filter capacitors right next to the bridge rectifier are brand new. Should I suspect them to be bad that quick?
 
. Across the two "AC/Wave" inputs: OL (switched the probes and read .456V)
2. Across the postive output and wave input: 0v (0v after switching the probes)
3. Across the negative output and wave input: OL (.458 after switching the probes)
Check it like 4 individual diodes 1.AC1---- pos , 2. pos ---- AC2 , 3. AC1---- neg, 4. neg ---- AC2..
of course measure the forward and reverse of each diode.
Due to being connected directly to the power transformer you need to check it out of circuit.
 
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Double check there polar orientation ( +....... -/+..........-)
About to remove the 2 filter caps for testing. Should I use a resistance check on these?

Check it like 4 individual diodes AC1---- pos , pos ---- AC2 , AC1---- neg, neg----AC2..
Ok. Here is what I got:
AC1----pos - .461V
pos----AC2 - 0V
AC1 ----neg - .459V
neg ---- AC2 - .461V
 
I just ran a resistance check on both filter capacitors. They both continued steadily rising on the DMM. No OL errors or high readings in the Mega-ohms.
 
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