Tek 465 5v Rail Issue

[RossH]

Newbie-to-Tek-scope-repair here. I was given a 465 for free. I would like to repair it.
Initial symptoms as reported by previous owner: no activity on panel upon startup, fan only.
Initial power-off inspection and investigation: nothing showed on visual (no dry soldering, no burnt or otherwise iffy-looking components). Didn't smell anything that was suspect. Continuity all good with fuses, plug to switch activation, etc.
Power-on investigation: all rails showed good except the 5v, it tested -0.45. Re-examination of 5v area using a 30x loupe showed a cracked rectifier (no other abnormalty, such as burning, etc). Pushing on one side with a dental tool caused the halves to shift slightly.
I replaced the rectifier, double-checked solder joints, and powered up. The rectifier unsoldered itself within 3 sec. I removed the rectifier and re-checked the other rails, all good.
So, what likely happened?

 

[bertus]

Hello,

When the rectifier gets so hot that it unsolders, there must be a short somewhere.
Does the PCB have tantalium capacitors mounted?
I have many times seen them create a short.

Bertus

 

[RossH]

Yes, tantalums a-go-go. I haven't checked those yet and should have first. However, I know they're a potential problem and will likely replace them as a prophylactic measure since I have to unsolder one side to test anyway.
I figured it's a short somewhere, but I wanted some input before proceeding further. This time I'll be a good boy and follow the isolation procedure for that rail.

 

[davenn]

I figured it's a short somewhere, but I wanted some input before proceeding further.

tant's often fail short cct
Takes me back 12 years to when I got my 2 x Tek 465B 's up and running. Still have one on the shelf behind me.

I will do some looking back to see what I discovered

 

[davenn]

@RossH

Here's the 5V rail starting point and a couple of the other rails




NOTE: if the +55V rail is missing, then so will the 5V rail and several of the other rails


Dave

 

[RossH]

Thanks, Dave. Ya, I've been going over the schematic and wondering about the cans. I may have to just dismantle this further than I wanted to. All other rails are good.

 

[RossH]

tant's often fail short cct
Takes me back 12 years to when I got my 2 x Tek 465B 's up and running. Still have one on the shelf behind me.

I will do some looking back to see what I discovered

Thank you, that's a nice offer!

 

[73's de Edd]

C1559 ?

 

[RossH]

That is the tant I thought would be a good candidate. C1552 also caught my eye, but wasn't sure if it was as good a candidate for the BIG melt. I'm new at oscilloscope and PCB work and I'm drawing on my tube radio knowledge to attempt this. I must admit I'm loving the learning experience and all the help I'm getting from you all is much appreciated.