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Sansui 6060 - power on issue
Sansui 6060 - power on issue
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Old 5th June 2019, 03:53 PM   #1
DanielSpokane is offline DanielSpokane  United States
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Default Sansui 6060 - power on issue

Hello,
I have a Sansui 6060 that was my dad's growing up. It's an amp that we've used for a lot over the years and love it (both for the sound and the memories).

However, recently I have some problems with it. What it does is this: when I push the power button and turn it on instead of hearing a "click" shortly after the power button is engaged and the sound turns on, instead I hear nothing and the sound does not turn on. Occasionally after waiting a little bit I hear the "click" (which I assume is a relay) and then the sound works fine. But increasingly I do not hear the "click" and there is no sound.

Any one ever run into this? Any ideas on how to diagnose and fix?

I've done a fair amount with guitar tube amps, but never with receivers which seem a fair amount more complicated.

Any help would be very much appreciated. I have VOM and Oscope if needed.

Thank you!

Daniel
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Old 5th June 2019, 04:59 PM   #2
nigelwright7557 is offline nigelwright7557  United Kingdom
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Its the protection relay circuit possibly.
I would check for DC offset on output of amp after relay clicks to see if there is a bias/offset problem.
Protection circuits tend to have a few electrolytics in them and they age and can start causing problems.
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Old 5th June 2019, 06:04 PM   #3
DanielSpokane is offline DanielSpokane  United States
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Thanks nigelwright7557.

I looked over the schematic and did my best to locate the bias circuit and relay (sorry for ignorance if I'm not looking at the right area). See attached. Would I just check to make sure each of the spots located in the attached schematic have the same voltage. If so, what should that voltage be? The capacitor says 50V; but the orange highlighted portion on the schematic (which is very hard to read) I believe says 37V. I assume I should check to make sure both are at 37V. If not then replace C519 and C520?

Do you think I should replace the Relay as well?

Thanks again.
Attached Files
File Type: pdf 6060 Schematic Excerpt.pdf (783.1 KB, 45 views)
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Old 5th June 2019, 06:20 PM   #4
Mark Tillotson is offline Mark Tillotson
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Any electrolytic cap in something of that vintage(*) is suspect. The amp should really have a recap, otherwise a whole slew of issues will be cropping up in the next decade or two. To start with the protection circuit should be recapped (its important it does its job properly), and then the power amps (which are likely to have run hotest). Also worth carefully removing any dust and grime build-up.



(*) 40 years or so according to a quick search.
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Old 5th June 2019, 11:00 PM   #5
mbz is offline mbz  Australia
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Two probable scenarios.
Fault in power amp stage resulting in excessive Vdc being placed on the speaker line.
Protection circuit doing its job of not activating the relay thereby protect the spkrs.
Fault in protection circuit, it doesn't activate the relay after the mute period.


For power amp issue, measure dc voltages between emitter resistors to ground/chassis

to identify problematic channel
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File Type: jpg 6060.JPG (86.0 KB, 141 views)
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Old 6th June 2019, 06:11 AM   #6
Ian Finch is offline Ian Finch  Australia
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The circuit still works but the relay drive timing caps have most likely dried out and become unreliable, as nigel pointed out. Specifically, the small timing electrolytic associated with start-up delay is likely dying but so will most other electrolytic caps in there, after 40+ years.

You could try replacing just C601, C602 (preferably with ≥ 16V types) but really, after 40+years, the whole lot of electrolytic capacitors will need replacing. If you can't identify what electrolytic caps look like, it might be wise to enlist professional help. Audio repairers are fully familiar with the need and are usually pretty quick at this.
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Old 6th June 2019, 07:01 AM   #7
DanielSpokane is offline DanielSpokane  United States
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mbz - I checked the voltage between the emitter resistors; both locations were 35.7V DC to ground. What do you think? That look ok? … what should I check next?

Ian Finch - thanks for the input. It does seem like if there are caps responsible for the relay opening, they would be suspect. Replacing a couple caps shouldn't be a problem. I was looking and can see where 601 and 602 are in the layout but can't find them in the schematic. Am I missing them?

Regarding having a tech do a full cap replacement... what do you think something like that would cost? It looks like there has to be 40 or 50 electrolytic caps in this thing.

Thanks!
Daniel
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Old 6th June 2019, 07:35 AM   #8
DanielSpokane is offline DanielSpokane  United States
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Another data point...

The manual has a procedure for adjusting the bias current. I attached a copy for reference.

I made some measurements:

1. Step 1 - at R05 and R07 - I measured 33mV initially and it slowly climbed and seem to somewhat stabilize at 39mV (although it seemed like it kept climbing).
2. Step 2 - at R06 and R08 - I measured 49mV initially and it slowly climbed to about 54 mV and somewhat stabilized (although it seemed like it kept climbing).

It seems weird that the DC voltage kept climbing. Is that normal?

The procedure calls for these to be adjusted to 15mV +/- 1mV. Since the value I measured is quite a bit higher... seems like maybe this is the culprit? Looks like I can adjust VR01 and VR02 to reduce. Maybe that will fix it? I would love to get some input before I proceed further and start changing things.
Attached Files
File Type: pdf Bias Adjustment.pdf (485.5 KB, 13 views)
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Old 6th June 2019, 10:31 AM   #9
mbz is offline mbz  Australia
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Quote:
Originally Posted by DanielSpokane View Post
mbz - I checked the voltage between the emitter resistors; both locations were 35.7V DC to ground. What do you think? That look ok? what should I check next?
Daniel

If you measured correctly then that would not be good.
There will be some transients immediately at power on and for a few 3-5
seconds after that. The emitter resistors are typically large (1inch x 1inch).
You would be unlucky to have failures on both channels, typically such
voltages would be caused by shorted output transistors, eg, c-e short.
Suggest recheck your measurement, maybe measure at the relay itself,
then consider diode testing output transistors (amp powered off/unplugged)
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Old 6th June 2019, 05:46 PM   #10
DanielSpokane is offline DanielSpokane  United States
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Attached is a scan that shows where I tested and the values.

I measured 35.7V at the intersection of R08/R06 and at the intersection of R07/R05. I used the transistor heat sink / housing to ground to. Is that ok? If 35.7V is too high... what value should that be? Both channels work fine and the receiver sounds great when/if the relay engages. So I'm guessing maybe if the voltage is way off I measured wrong?

Regarding the bias current measurements. I highlighted the measurements I took. As shown in the attached sketch both 49mV and 39mV is way out of spec. It looks like I can adjust it to spec (hopefully) using VR01 and VR02. Should I do that and see if it fixes things? It seems to me since this is way out of spec and directly tied to the relay it is definitely highly suspect?

Also Ian Finch suggested replacing C601 and C602. I can do that, and found them in the schematic (see attached schematic excerpt 2)... but want to confirm those are the capacitors that are responsible for timing on opening the relay? I'm having trouble understanding from the diagram how these relate to relay opening timing. I'm not super savvy at reading diagrams so will trust your input... but want to confirm.

Thanks again everyone!
Attached Files
File Type: pdf Bias Current Test Results.pdf (633.9 KB, 13 views)
File Type: pdf Schematic excerpt 2.pdf (863.6 KB, 20 views)
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