Yamaha CA-800 protection relay not working

[mbz]

We'll proceed to connect the 220V transformer, which is currently set to 230V, correct?

Your transformer is wired for 220Vac
Consider changing the wiring for 230Vac operation

 

[mbz]

Do you have a photo of the psu/relay board before you started removing parts?
Make my job a bit easier

 

[mbz]

A note about 2SC458LG, pinout is ecb when looking at the front/bevelled face
or bce when looking at the large/printed face. Replace with KSC1815 or KSC1845
depending on operating collector current.

TR705 2SC458 ecb KSC1845/KSC1815 ecb icon ok, orientation appear incorrect, rotate 90deg CCW, middle collector leg pushed back
TR706 2SA572 ecb KSA992 ecb appears ok
TR707 2SC458 ecb KSC1845/KSC1815 ecb icon ok, orientation appear incorrect, rotate 90deg CCW, middle collector leg pushed back
TR709 2SC458LG ecb KSC1845/KSC1815 ecb icon ok, orientation appear incorrect, rotate 90deg CCW, middle collector leg pushed back

I may have got these wrong since looking at negatives is confusing. Certainly those 3 transistors are not correct.

 

[mikevinci]

Do you have a photo of the psu/relay board before you started removing parts?
Make my job a bit easier

Of course, this is the situation before the transistors were replaced.

 

[mbz]

Of course, this is the situation before the transistors were replaced.

Confirms board icons for TR705, 7, 9 are correct.
Your replacements are incorrectly orientated. KSC1845ecb to match board icon

 

[mikevinci]

Su transformador está cableado para 220 V CA.
Considere la posibilidad de cambiar el cableado para su funcionamiento a 230 V CA.

Modifiqué el cableado del transformador para 230 V, y ahora la medición entre los cables amarillos es de 104 V CA.

Sin embargo, sigo midiendo 70 V CA en los terminales +/-B.
Mediciones
D706: cátodo +76V, ánodo 20mV

 

[mikevinci]

I've changed the orientation of protection transistors 705, 706, 707, and 709. I haven't connected the power stage yet until the voltage is within the correct range of ±50V for now, and I've noticed the relay clicks after power-up.

 

[mbz]

104Vac between yellow wires is ok

Sin embargo, sigo midiendo 70 V CA en los terminales +/-B.

I assume you mean 70Vdc

D706: cátodo +76V, ánodo 20mV

Strange that D706 cathode has not changed (post #27) after rewiring of transformer

I've changed the orientation of protection transistors 705, 706, 707, and 709.

Please post pix showing new orientation.

Do you have an oscilloscope? Capture waveform at D706 cathode. Otherwise measure AC voltage at D706 cathode, black meter probe connected to black speaker connector/GND

Have you diode tested D701 and D702?

 

[mikevinci]

I cannot lower 70V DC to the rectified voltage of the protection relay board. I replaced the D701 and D702 diodes with new MUR1620CT and MUR1620CTR diodes to guarantee the durability of the equipment and I can replace them with the original ones but it remains the same. When taking measurements of new and old diodes, the board does not show any apparent gaps.

Could it happen that these diodes are damaged and cannot be detected due to the excess voltage that was present before modifying the input voltage of the transformer?

If that's the case, why can I replace these diodes temporarily to try and buy permanent ones?

In my desperation I also soldered the diodes D703, D704, D705 and D706 to ensure that this voltage was not affected, but I continued to advance the same way.

 

[mikevinci]

104Vac between yellow wires is ok


I assume you mean 70Vdc


Strange that D706 cathode has not changed (post #27) after rewiring of transformer


Please post pix showing new orientation.

Do you have an oscilloscope? Capture waveform at D706 cathode. Otherwise measure AC voltage at D706 cathode, black meter probe connected to black speaker connector/GND

Have you diode tested D701 and D702?

I performed the measurement between ground, black speaker connector and D706 cathode in AC but I did not observe any apparent AC or a very very low value of 0.053

The new location is as follows which is how I believe they should be installed according to the silkscreen printing on the plate, but the relay is not click. However, when TR709 is installed as in the third photo (IMG_7423), it does click instantly upon power-up.

 

[mikevinci]

I cannot lower 70V DC to the rectified voltage of the protection relay board. I replaced the D701 and D702 diodes with new MUR1620CT and MUR1620CTR diodes to guarantee the durability of the equipment and I can replace them with the original ones but it remains the same. When taking measurements of new and old diodes, the board does not show any apparent gaps.

Could it happen that these diodes are damaged and cannot be detected due to the excess voltage that was present before modifying the input voltage of the transformer?

If that's the case, why can I replace these diodes temporarily to try and buy permanent ones?

In my desperation I also desoldered the diodes D703, D704, D705 and D706 to ensure that this voltage was not affected and replaced the ceramic capacitors with the original ones, but I continued to advance the same way.

 

[mbz]

Could it happen that these diodes are damaged

The MUR diodes are high current items, they will not be damaged

I also soldered the diodes D703, D704, D705 and D706

D706 cathode (=0V) indicates a problem (D704 failed short then D706 failed open??)
What is strange is both +ve and -ve rails affected.

Suggest replace all 4 zener diodes, 0.5W, buy a few spares. Replace then dbt power up.

I performed the measurement between ground, black speaker connector and D706 cathode in AC but I did not observe any apparent AC or a very very low value of 0.053

D701,2 working OK

The new location is as follows which is how I believe they should be installed according to the silkscreen printing on the plate, but the relay is not click.

The relay should not click because you have 0V at D706 anode, the board icons are correct.
Need to fix these zeners

 

[mikevinci]

I replaced the four Zener diodes and reassembled everything. I turned it on and it reads 72.95V DC. It's incredible, I can't figure out where the problem is. The relay isn't activating, of course. ‍‍

Measurement between D706 cathode and black speaker connector = 72.95V DC; between D705 anode and black speaker connector = 72.95V DC

Upload photos

 

[mikevinci]

Would it be interesting to see photos of the back of the license plate?

 

[mbz]

Would it be interesting to see photos of the back of the license plate?

Post a photo of the relay/psu board solder side

 

[mbz]

Measurement between D706 cathode and black speaker connector = 72.95V DC; between D705 anode and black speaker connector = 72.95V DC

D705 anode minus 72....

Possibly the zeners have blown immediately at power on.
Prefer to have used a DBT.
Also measure voltage at D706 anode expect about +20Vdc, 0V indicates blown
also measure D705 cathode expect -20Vdc, 0V = blown
If blown, replace then dbt power up.

 

[mikevinci]

Ánodo D705 menos 72....

Es posible que los diodos Zener se hayan fundido inmediatamente al encender la alimentación.
Preferiría haber utilizado una DBT.
Mida también el voltaje en el ánodo D706; espere alrededor de +20 V CC, 0 V indica que está quemado.
También mida el cátodo D705, espere -20 V CC, 0 V = quemado
Si está fundido, reemplácelo y luego enciéndalo.

Ánodo D705 menos 72.... correct sorry -72v

The reading is 0V at both points. Is the DBT lamp a series lamp? I use it constantly, and the bulb remains dim, with almost no light coming from the filament.

'll replace the diodes again, but could the filter capacitors C705, C706, C707, and C708 be affecting it? They were also replaced, but perhaps that's the only thing I haven't replaced yet.

 

[mikevinci]

Post a photo of the relay/psu board solder side

 

[mbz]

Is the DBT lamp a series lamp? I use it constantly,

Yes, series lamp. Without it the voltages will be slightly higher.

edit
Please double check your zener diodes,
D703, D706 0.5W 31V
D704, D705 0.5W 21V

 

[mikevinci]

Hello, I replaced diodes D703 and D706 (0.5W 46V) and D704 and D705 (1W 22V), which were the ones I had available. The measurement now with DBT is +B 64V and -B -70V. When I turn on the relay, it activates after 3-4 seconds.

Why is it still maintaining -70V on the negative rail?

I think we're on the right track.

I'll buy new diodes according to the specifications (31V and 21V) as soon as I can

Could I try connecting the power stage and verifying its behavior?