Ampeg B4R Issue

[hodgy]

Hi Folks, loving this forum- very informational.
Here's the problem I'm having with an Ampeg B4R:

Power on the amp- no fan, signal OK. POPs, then the fan starts, no output signal. Flick the switch off. Repeat.
This will happen 3 or 4 times until the amp 'warms up'.
Then the amp powers up fine, fan runs, signal is good.

The failure is very consistent, already checked the usual bad/cold solder joints and what-not.
Any ideas? Thanks!

[booj]

Maybe there is a delay circuit which turns the speakers on after a short warm up? A schematic would help the diagnosis.

[hodgy]

Actually the speakers come up pretty much right away (this is a solid state amp). I'm not sure if the fan is supposed to start right away or if it waits until the temp sensor hits it's kick-on point. Pretty simple circuit there with an LM-35 (temp sensor IC) coming off of each channel into a TL072- half of it going to the 'Fan Speed Control', the other side going to 'Over-Temp Protection' before splitting off to Relay A and Relay B. Seems to me like on of the LM-35s or the TL072 is acting wonky. Dang, I may have just answered my own question.

[bassman57]

I had the same problen with mine awhile back, last year. I replaced the fan and it solved my problem. I can't find a real schematic manual for this unit yet. The owners man hasn't enough info. Mine is not even pwring up although I used it not long ago at an event. Help!!!