Bosch CDI 3 pin experts only

[HKZ Bob]

Dear Folks,
I need to replace the Bosch Diodes after the transformer
D7 & D1.
I like you opinion. I am going to use two BY 255 Si-Di 1300 Volt 3A
or two the 1N5404 600V 3A.

I assume both will work.
Does anybody have some experience in replaceing these types. The BY 255 has a bigger pin diameter.

Or would a 1N 4007 will work as well. I ave not measured the
coil back response in value.

Greetings Bob

[HKZ Bob]

I will post the schematic. Just a second.

[HKZ Bob]

[HarryD]

Bob,

I do not know much about this topic but if it was me, I would do a search on CDI and for posts by early_s_man. You will find a wealth of knowledge on this topic.

[HKZ Bob]

Hello Folks, who has Data sheet of the original Bosch parts.

Thyristor:
QT104
T6N 500 COB 1 227 030 010
T6N 600 COB AEG 8 925 305 345

Zener Diode
BZY 85/C6 V 8 8 905 421 690
ZX 82 ITT 8 905 421 564

Diode SHG 1SB ITT 8 905 131 051
Diode 0 270 000 003
Diode 0 270 000 001
Diode D1/1000 AEG 9 905 605 701
Diode BAY 38 Valvo 8 905 405 250

Übertrager Bosch 1 224 120 002

Hope you can help.

[azasadny]

Wait for Warren (early_s_man) to post, he's the man!

[ischmitz]

I think both will work just fine. Since the diodes are in series you have even more safety margin here. I would go with the 1N5404 since it is cheap and readily available. After all this is a simple rectifier application.

Good luck,
Ingo

[Early_S_Man]

I suggest using 1000 Volt rated 1N5408 rectifier diodes ... there is no difference in cost, and much higher PIV margin. It is far too much trouble unsoldering those 17 wires to risk using a 400 Volt diode at its' design limit!

[herman maire]

Does somebody rebuild these? I have 2 I would like to fix.

Also, whats the method to unsolder the wires? I tried this once with a cheap solder gun by melting the solder around the wire .... I ended up detroying the circuit bord Then I freaked out and through it accross the room

[HarryD]

Originally posted by herman maire
Does somebody rebuild these? I have 2 I would like to fix.

Also, whats the method to unsolder the wires? I tried this once with a cheap solder gun by melting the solder around the wire .... I ended up detroying the circuit bord Then I freaked out and through it accross the room

LorenFB (who posts here) offers this service. You can also contact Zim's (http://www.***********/acatalog/Rebuilt_CD_Box__911_69_77.html) or Otto's (http://www.ottosvenice.com/) to do an exchange.

[ischmitz]

Our host also offers a rebuild service here: http://www.pelicanparts.com/catalog/shopcart/911M/POR_911M_ELignt_pg5.htm

[Lorenfb]

"I would go with the 1N5404 since it is cheap and readily available."

Some seem unaware of the fact that the diodes not only "see" the peak inverter
voltage, i.e. 400 - 500 volts, but also the secondary voltage of the coil if a voltage
breakdown occurs, e.g. coil wire to primary CDI connection or a secondary to primary
internal coil voltage breakdown.

[HarryD]

Originally posted by ischmitz
Our host also offers a rebuild service here: http://www.pelicanparts.com/catalog/shopcart/911M/POR_911M_ELignt_pg5.htm

Glad to see Wayne offering the service. I did not see that page. FWIW, this service does not appear on the early 911 parts listings. THANKS!

[HKZ Bob]

Where to buy these replacement reasonable.

Thyristor: QT104 T6N 500 COB 1 227 030 010
T6N 600 COB AEG 8 925 305 345

Replace by
16RIA80
25RIA80s
50RIA80 @ $14.30

Zener Diode
ZX 82 ITT 10Watt 8 905 421 564
repalce by

1N 3003 B

ANY ADRESSES RATES

BOB