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CR-820 relay buzzing

Nuklhed

Nuklhed

Active Member
Hey team. Dug out an 820 that has been kicking the kiester for about 3 years. Got it to where I can actually turn it on without smoke and fire!
But the protection relay buzzes constantly. Measured 3.3 vdc and stable at the collector of TR805, so I imagine that a 12 vdc relay would chatter. Not sure where to go from here….all schematics I have access to are really crappy. Has been recapped and relamped with incandescents.
Any thoughts would be appreciated.
 
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check TR805e, expect about 15Vdc, if so then replace TR805. 3-10Vdc would point to psu D805, TR808,9.
 
mbz said:
check TR805e, expect about 15Vdc,
Click to expand...
If not..Check the voltages at both ends of R812 - 100Ω , 5 watt . Should be around 20 vdc on one end and around 15 vdc on the other.
 
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Thanks gents, I have an update. After I posted I decided to search the forum using some different search tags, etc. I found a post where the two of you helped a fella out with a similar issue. So, I replaced TR806 with a 15032g. Replaced D802 with a 4004. Replaced TR805 with a 1013. Replaced TR804 with an 1845.
Crossed my fingers and turned on. No chatter, thought I heard relay stay on. Hooked up iPad to aux, cheapo speakers. Volume to zero, pushed speaker button to on, heard pop, smoke from left speaker. My 8 ohm speaker is now a 0.5 ohm speaker!
Turned off, unplugged, grieved my speaker, back at it.
I should still be able to t-shoot as long as I keep my speakers off?
 
Yeah, would have been easier to test R812, this was a good suggestion, such resistors tend to drift high causing low relay voltage. Spkrs should not be connected, maybe you got the pinout wrong on one of the replacements?
 
With speakers off and unplugged, turned on fine. R812: 13.4vdc on transformer side; 21.2vdc on tuner side.
 
Pulled the left channel outputs. They are original Toshibas, tested good. I have some MJ21195 and 96 on standby.
 
Anything’s possible in the lab my friend! It was playing beautiful tunes on my 1040 just before I sent it to its death. It served me proudly for many years….
 
Nuklhed said:
Anything’s possible in the lab my friend! It was playing beautiful tunes on my 1040 just before I sent it to its death. It served me proudly for many years….
Click to expand...
Without any speakers connected. Measure the DC offset at the speaker binding posts.
 
Nuklhed said:
ight speaker terms 8mv; left is 35v
Click to expand...
Important to get the sign right, assume +35V, points to TR719, TR723. Diode test each, try incircuit first since looking for a short. If they pass then measure dc voltage for each, b/c/e to GND, guiding voltages are shown on the schematic.
 
Gents thank you so much for your help. Mbz I’m not familiar with the “diode test in circuit”. Could you please elaborate?
As avionic suggested, I did remove TR723 and it tested good out of circuit.
Always eager to learn any new test methods!
 
And I prefer my speakers medium rare…with some steamed asparagus and a full bodied cab.
And of course 2 fingers of Basil-Hayden for dessert…..
 
Got the following voltages today: all with reference to chassis.
TR723 B +34.8vdc, E +35vdc, C +45.4vdc
TR719 B +36.1vdc, E +35.6vdc, C +45.8vdc

Had the unit tipped on side….from bottom of board noted a spark from cathode of D804 when energizing? Solder looks good…took readings after.
 
Nuklhed said:
Mbz I’m not familiar with the “diode test in circuit”
Click to expand...
Most MM will have a diode test function/symbol. For proper testing the item to be tested should be removed from the circuit however testing with the item still in circuit may provide useful information.
Nice graphic from markthefixer on diode testing, red/black giving probe orientation, two results expected, 640mV (or abouts, 500-750mV) and OL open loop/circuit.

Nuklhed said:
TR723 B +34.8vdc, E +35vdc, C +45.4vdc
TR719 B +36.1vdc, E +35.6vdc, C +45.8vdc
Click to expand...
TR719b should be about +1.2V, unlikely C731 has failed short.
R735, 737, VR701...R743 forms something of a voltage divider. Voltage at D711 anode should be about +1.7V, expecting you have +36.6V abouts. Possible causes being VR701 failed open (unlikely) or TR707 is off so no current flow/volt drop.

Plz diode test C731, in circuit, it should ramp up, also resistance check VR701. TR707 b/c/e voltages to GND may help.
 

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Thank you so much for the great information. I will report back with results.
Btw, reflowed solder joint at D804. No more spark.
 
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