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Real Quick Question

B

BP101

Active Member
Hi guys. This should be an easy one. The Sanyo 2033 I listen to in my office works perfectly. However, when I turn it on (it has a power button, not a toggle switch), I get a brief "thump" sound. Then everything is fine.
Should I ignore it, or is it a sign of bad things to come? P.S. I totally de-oxited (?) the receiver about a month ago.
 
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I always turn the speakers off before I power down and then turn them on after the speaker relays have kicked in on power up.
 
you may have a problem with the DC offset. This will often present a thump when too high. turn down volume control zero (minimum), take a VOM or DMM (set to mv range) and check accross the +/- terminals on each channel. You should get well below 50mv (closer to 0mv the better). If not... you have a problem
 
I would remember how loud and how long is the noise today... and pay attention if it changes...
My amp started like that... just a noise when power on and/or power off .. Now the noise is much longer (like 10 seconds after I power it off... it continues) even with volume at zero. But of course I can't say that my noise comes from the same source as yours... Yesterday I measured DC offset: 8.2 Volt :(
 
Hmm...thanks everyone. I get the thump even with the volume at zero. But the thump has no sustain, just one quick "hmp!". I will do the DC offset test. If it serious, I might try to fix it, but it is so easy to find a cheap vintage receiver for $20 or less (I have about seven at the moment), I'll just swap it out with a backup rather than risk my speakers. Thanks again.
 
With some receivers (I'm thinking H/K 330c) this is normal and seems widespread. It means that your speakers are getting a burst of DC current at power down OR that your DC offset is high to begin with, and the WHUMP is caused by the speaker cond pulling back to its' neutral position when the power is shut off. As other posters noted, check the DC offset at the speaker terminals with the volume all the way down. If it's normal, I'd look and see if maybe your amp is cap-coupled at the outputs and have a look at those caps.
 
My STA-225 has a mild thump when power is first applied.
But the offsets are 12mV & 14mv for left & right. I wondered about that too, but read elsewhere here that is the norm.
I always volume down before I power down w/any of my units, as it is.
 
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dspear99ca said:
With some receivers (I'm thinking H/K 330c) this is normal and seems widespread.
Click to expand...

Yes. The H/K is probably direct-coupled at the outputs rather than capacitor-coupled. I've had many amps and receivers over the years that exhibited a turn on "thump" and all were direct-coupled designs. If a capacitor-coupled design is doing this, check the DC offset.
 
I can not find the service manual for this Sanyo 2033 anywhere. Hifi Engine only has the user manual. I got this for free and want to get it working. The only issue I was having is no sound on lower volume and staticy scratchy sound on high volume and left channel is completely void of any sound. I want to say it has to be the Power Supply Board or the Amplifier Board but once again no service manual. I am guessing that the pictures I have posted are the Power Supply plus more so I don't know where to start. Does anyone see anything or have any course of action here?
 

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I'm not sure if this model has a protection relay, or not. Is there a several second delay before you hear a relay click and music starts to play?
 
redk9258 said:
I'm not sure if this model has a protection relay, or not. Is there a several second delay before you hear a relay click and music starts to play?
Click to expand...
No there is no click and I can not find a relay and I can not find the service manual on line. I may have to buy it somewhere.
rickl said:
I'd look for the protection relay and find a replacement. Post the part number if you are unsure.

Your symptoms seem like a output relay problem.
Click to expand...
ricki, can you be more specific? Is an output relay and output transistor the same thing? Once again no schematics.
 
Are these concerns? This is all I can find that looks suspicious.
 

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OK I got tired of waiting and replaced this capacitor and the one transistor.

The sound is still scratchy and you can make out the beat but you can not understand the words, but now I have sound from both the left and the right channels. So I am halfway there.

Found another suspect transistor. What do you guys think?
 

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Are one of these the protection relay?

I think the second one is called a Snubber Capacitor or relay???

In the first pic is that a protection relay on the end of the power switch?

How do I test these?
 

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Those oxidized legs on transistors can certainly cause static, pops, etc. There is a thread here about certain transistors that do not age well and cause issues.

I think that is part of the power switch. I have never seen one of these units in person. Most but not all receivers have speaker protection relays. What is the behavior at power on. Is there a several second delay before sound passes to the speakers? Or do you have a thump and immediate sound?

dlucy

Thread 'Top Ten Worst Transistors - noisy, failure-prone, whatever... and replacements'

I've followed AK advice for several vintage solid state receivers now and the difference in sound, from recapping and from replacing "known-to-be-noisy" small signal transistors to be amazing.

While following along with others' threads and trying to help out with "consider replacing these known-noisy transistors", I've tried to find a "top ten list" or "worst transistors" thread, but found none.

If there is a long-standing "which transistors go bad or go noisy and you should replace when you can" thread, please post a link.

If not, please contribute your "worst, replace ASAP"...
  • Like
 
PioneerPro said:
No there is no click and I can not find a relay and I can not find the service manual on line. I may have to buy it somewhere.

ricki, can you be more specific? Is an output relay and output transistor the same thing? Once again no schematics.
Click to expand...

it may not have a protection relay. Without a schematic, i'm just guessing. the Sanyo 2016 doesn't have a protection relay but the 2050 does.

if you don't have a schematic you are kind of running blind. maybe inject a signal and start looking at various places with your scope.

This won't be easy and will require some experience.
 
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