Markbass Little Mark II a new post

[Techknowman]

Ok here are some captures of waveforms from 6 critical places in the circuit
R76 at pin 7

R77 at pin 5

Pin6

C70 +

Pin8

Pin 2

[Enzo]

I don't know what the original was, but I got the impression your IRS2153 was maybe a substitute for something else? Is that the case, or am I reading something into your sentence that isn;t there?

I did install a IRS2153D in the place of IC5,

If I read it right, there is some difference between the data sheet for that part and the schematic with regards to pins 2 and 3 wiring. (And of course the 1 and 4 thing)

[Steve Conner]

I'm puzzled. The schematic in the Markbass service manual doesn't show a bootstrap diode. (That would be D2 in this schematic: http://320volt.com/wp-content/upload...53_40v_15a.gif)

The bootstrap diode is needed for the high-side of the gate driver IC to work, and the scope shots posted seem like what I would expect if it was missing. Maybe the old gate drive IC had it built in and the new one doesn't?

If that isn't it, another thing to check is the aux supply: C67, D34, D39, C69, R80, D21, C70, D40, C52 etc. The power supply is supposed to start like this:

C52 charges from the DC bus through R78. When it reaches the gate driver's lockout threshold, the driver bursts into life. But the current through R78 is not enough to run the driver continuously. So, before C52 runs out of charge, the aux supply is then supposed to come up and keep the driver going through D40. If the aux supply isn't working, you will just get the little ticks.

This is an example of a "kickstart" circuit, known for being a nightmare to troubleshoot. Maybe the design is just marginal, and C52 needs to be bigger to support the new version of the gate drive chip. Oh, and check R78 hasn't drifted grossly up in value, and C52 hasn't dried up.

[Techknowman]

Enzo you are correct about IC5 being a sub. knowone but mark bass amps knows what IC5 really was. they sand the numbers off.
The consensus from another post on this forum. http://music-electronics-forum.com/t10881/
was that it was a IRS2153D, i'm doubting that myself seeing what the waves are doing.
I also agree with you steve that the kickstart is failing. this is shown in the pin 8 bootstrap voltage slowly dying off and then kick starting again. I'm going to look at the other offerings from International Rectifier and see if there is a better fit.
Thanks for all the help. We will beat this thing yet. I hope!

Update.
While looking at the data sheet there typical application diagram shows no bootstrap diode and they show and internal bootstrap fet.

Im thinking it should be a IR21531DPBF

[Techknowman]

Well using a IR21531DPBF, the power supply works.

A IRS2153D does not work! I miss read or something. the other post clearly said IR21531DPBF

Put the IR21531DPBF it works put the IRS2153D it does not work!

Now when I connect the +/- 80V buss the power supply won't start. reading +voltage on the speaker output and the protection is staying set. with the +/- 80v busses disconnected the power supply starts up fully and the protection relay will click in.
So i have issues inside the power amp section to fix.
Glad to have the power supply working!

[Enzo]

"Great shot kid! Don't get cocky." -----Han Solo



Progress is progress, regardless how incremental.