Vintage Products

Re: Beocord 1600 : Magical missing capacitors!

PCPete — Sat, 26 Jul 2008 22:37:54 GMT

Thanks casdave, that's exactly what's happened. The tants (especially on the preamp boards) have long since turned into, er, dynamic resistors. I changed the two in the preamps, and the hum and crosstalk disappeared from the preamps.

I've just got around to getting a big bag of good quality, low esr, high temp electros, and that's when I noticed none of the polys or ceramics were mentioned in any of the BOMs. And I agree, they're probably going to outlast me, unless they get overheated or crack. So it's not a big deal.

This latest saga came about because I've been getting huge amounts (tens of volts!) of hum on the outputs, and the main amp heatsink has been getting extremely hot to the touch.

So I did some troubleshooting, and I found the main rectifier was also getting hot, especially on one side. And when I verified the steady state voltage, instead of 30V DC, I was seeing 36VDC with 200mV RMS ripple (which is really wierd for this power supply), and worse, instead of -11.4V on the downstream side of the main pass transistor, I was getting -1.42V plus ripple.

I've just spent two hours checking every component on the psu, and despite seeing all the wrong voltages, all the components checked out perfectly (except the caps, but they don't explain the fault). It was driving me nuts (more nuts than usual).

I pulled off the front panel (I replaced the headphone socket a while ago, and accidentally shorted the outputs agains the front control panel, but I figured that out quick and no damage was done), and the turntable plate, and hey presto! the voltages were all back to normal, and nothing got hot.

It turns out that when I replaced the EOT kicker transistor (TR30) a while ago, I reused the TO5 heatsink and carefully bent it so the TO192 replacement could cool down... and I warped one corner just enough so it contacted the turntable plate, but only when it was pushed fully home.

That was why I was getting 11V sparking across the playback cover, and why I kept blowing the kicker transistor and cooking the kicker coil.

So there was the explanation for a whole bunch of seemingly completely unrelated faults over a 12-month period. And the snr for the playback is stupendously good now. It just goes to show.

Cheers,

"Leaky" Pete

Re: Beocord 1600 : Magical missing capacitors!

casdave — Sat, 26 Jul 2008 05:05:37 GMT

It's really just the electrolytics that need replacement, other types last much longer, disc ceramics can be found in equipment well over 50 year old and they still function perfectly.

The only other ones that might of concern are tantalum capacitors, they are usually more reliable than electrolytics, although I have known them to fail.Even so, I would not make tantalums much of a priority to replace.

Beocord 1600 : Magical missing capacitors!

PCPete — Fri, 25 Jul 2008 02:12:08 GMT

G'day all,

I'm in the process of repairing my old friend the Beocord 1600, and I've discovered more than a few leaky capacitors (tants and electros), so I went through the 1600 TRM kindly scanned by Peter, and got a list of all the caps so I can do a complete swapout.

Much to my surprise, there is no mention of any ceramic or MKT/poly caps anywhere in the manual! I've got all the electros, they're all clearly listed, but not the ceramic or other caps.

Can anyone confirm that using the "least dissimilar" cap replacement will work for any of these caps (just the ones that need replacing)?

By that, I mean I would replace ceramics with 100V ceramics, poly's with MKT or poly's or greencaps of the same or higher V rating, and others (like the capstan motor starter, 400V disc ceramics, etc) with modern "uprated" replacements?

In other news, I have around 250 photos of the re-belting and turntable adjustments for inclusion in a how-to guide. But I keep finding more things to fix before I get time to upload some helpful material... I promise it's in my to-do list (I owe a lot of people)...

Cheers,

Pete