CS400 PowerBoard - 1979

[Hans]

Hm, do we have two forums and two threads ? I'm confused ... or cause confusion myself ... let me suggest to let this one die, there was one famous word from Mr. Highlander about only one ...

[Hans]

Just had time to check the one, working channel. One bit concerns me, if it is working at high power on 8 Ohm speakers, the transistors become quite hot very quickly and the entire cooler as well ( as it should be). After a while the temp switches cut the power which I consider ok. I checked and all transistors become hot quickly, so all are working. The sound is ok, no distortion. but the clipping LED is on at high load.
Q: Do these amps really become that hot ? Remember there's only one working channel at present, how hot will it be if both channels are working ? The + / - Voltage is on 61 V, on high load it is at about 51 V (+/-).

[km6xz]

Just a question....how do we all get one of those fancy Enzo-double-postalizers? I am jealous, when I post, only one single measly post is seen. When Enzo posts he gets an automatic repeat in case no one paid attention the first time....

[Hans]

All right, the problem is clearer now, the channel I'd thought working perfectly turned out to have a faulty driver board. After, lets say 4 minutes, the power reduced to 51 Volts and the transistors on the power board became hot. I swapped the driver boards and all is perfect. The faulty driver board always starts good but after a few minutes it fails again. Do you have an idea what this could be ?

[km6xz]

Is it getting hot with no load? Be sure the thermal tracking diode mounted on the heatsink is working. If it is open, it will cause a higher voltage difference on the bases of the driver/output transistors and they will get hot from conducting almost the full cycle, sort of AAB class.
Measure the voltage drop across the emitter resistors to see how much current they are really dealing with. Try shorting that thermal diode stack and see if it cools down. If it does, the driver is probably OK.

[Steve Conner]

Just a question....how do we all get one of those fancy Enzo-double-postalizers? I am jealous, when I post, only one single measly post is seen. When Enzo posts he gets an automatic repeat in case no one paid attention the first time....

It's an annoying quirk of the latest version of the forum software - depending on what browser you're using, the phase of the moon etc., posts will sometimes be duplicated

Although in the case of Enzo's posts, most people could benefit by reading them twice

[Hans]

Thanks to my holidays I had a few minutes aside gardening ... there is one driver transistor on the driver board broken, B-C short cut in both directions, spare parts ordered. Now I'm off for a few days in the UK, so long and thanks for your help so far.

[Enzo]

Yeah, I try to think to delete those. It is annoying. I hit POST and it sits there thinking. After a time it asks me if I really want to leave the page. When i say yes, it takes me back to the forum, but leaves two posts. Other times I try to post, and it warns me I have to wait 28 more seconds before posting "again." Not sure what to do about it, since I am computer illiterate.

[damianh12]

nesecito el diagrama de este amplificador no lo puedo bajar CS400_pwr_sch.pdf

[Enzo]

Try this: