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PreSonis Eureka / Processor

R

RadioRickster

Anyone happen to have schematics scanned for above - looked on vendor's site with no luck. We use several of these and it appears on one the low end response is suffering and overall output drive is weak. Looks like 2 op-amps inside that can be changed out, but no markings on them (or, at least they are difficult to read). Any tips about this unit is greatly appreciated.

Rickster
 
Frequency roll-off--"telephone effect"--usually a sign of leaky caps. IC's either work or don't.

Shot-gun all the electrolytics.
 
Thank you for responding TomT and dtube1. I didn't e-mail them... yet, but I'm getting ready to. There are three large 50vdc 3300mfd electrolytic caps near the power supply section across from three voltage regulators. The front cap is not flush with the board (looks lifted and tilted), but that could also just be poor QA from the factory. The numbers for the 2 op-amp chips are micro-etched and almost impossible to see without a jewelers eye loop. I keep coming up with NE5534AP. Time to pull the front end, release the rear connectors and yank the board(s). The station has 2 other units in a different studio that work fine, so I'm hopeful this one will come back to life without too many headaches. Thanks again for the responses.
 
The filter caps are probably $2 or $3 each from Mouser. Also need to change any smaller coupling and bypass caps, usually in the range of 22 to 100 uf, on the board. Ne 5534 are common chips--if they are socketed you can change them if you want, though if the unit was working they are not likely to be the problem. If they are soldered to the board & the unit is working just leave them alone. Difficult to change unless you are experienced in this type of circuit board work.
 
Hey Tom,
The -20 and 0 db leds are constantly lit, while the 3rd clip led jumps on at about 25% gain increase. This makes no difference on the actual gain or frequency response at output. Plus, noise floor is through the roof. Contacted PreSonis and they are sending the cap (and meter bulbs... it needs those too), but I also suspect op-amp failure. Those are plug in. Life would be so much easier if haden't loaned my scope out years ago (never got it back). :-\
 
I don't know anything about these processors, but filter caps are probably not the right answer. Bad filter caps result in audible hum in the output. Coupling caps could possibly be the problem. Typically, these will be near the input connector and again near the output connector. They may be non-polar. There may also be some between stages. Other than the filter caps on the power supply, typically, the caps that are the largest are the output coupling caps. You can easily determine if they are bad by running a frequency sweep into a load, like 600 Ohms. Then run the same sweep into a bridging load (more than 10 kOhms). If the 600 Ohm sweep has substantially more bass roll off, then the problem is the output coupling caps. If not, then they are good and the problem is elsewhere.
 
Hey Kmagrill,
Schematics would help, but there's really only a few places a tech can pull and replace things. Practically all the resistors are wave-soldered microchips and there are only a few electrolytics that can be yanked. Still waiting for PreSonis to send that 3300 cap to replace the one that's lifted near the power supply. Next step are both op-amps (plug-ins). After that, she becomes a glorified spare parts unit for the other 2.

Thanks for the reply. I'll keep the board posted as I progress.

Rick
WXJB
 
Mouser.Com

No minimum order, but you will have a hard time breaking $25 in replacement parts. They're in Texas, usually no more than few days shipping even with ground UPS.

You can order the 3300 volt caps from them (they have both radial--leads at the same end, and axial types--leads coming out of each end. Just make sure you get the same or larger voltage rating. May also want to find a metric ruler to make sure you don't get one that is too long or too high (e.g. radial). They also have the NE 5534 chips.

A bad IC would likely run hotter than the others, but these are cheap chips --try 94 cents each.

IC: Mouser Part No. 595-NE5534PE4

Axial 3300/50 volts : Mouser Part#647-TVX1H332MDD $8.19 (35 volts would be cheaper)
Radial:647-UVR1H332MHD; $2.25
 
Just to keep the group posted, I ruled out the caps. The one 'suspect' cap was only lifted on one side because there's not enough clearance next to the other caps to placing it flush on the board. Simple design oversight, otherwise they all checked out ok. So, I ordered 2 op-amps from Mouser. Oh, before I forget - one warning: unless you have a 10X jewler's eye loop handy, be ready for a heck of a time changing the meter lamps. I did it, but it was a royal pain in the rear. The holes in the lamp board are 'microscopic' and it was a challange getting the old solder out.

Rickster
 
Low end issues (tinny sound) and weak output sound like a cap problem to me as well. Recently finished several channels on an Auditronics 200 series. Tinny sound and weak output = bad caps everywhere.
 
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