Help with intermittent Alesis RA-150

[solartony]

docSanchez;182882 says:

I have the service manual for the RA-500, which has the same PCB:
===============

hi ya'll, same RA150 model here, powers up, red led's stay on for the 4-5 secs or so,
relay clips, blue led does not come on ... no sound ...

R401/R402 are discolored, they get hot ...impossible to see markings,
the RA500 power supply diagram shows their values at 180 ohms ...

i took one leg out, both measure 470 ohm within a few ohms of each other ... mmmm ...
coincidence ? ... which one is right, the diagram or the resistors ?

anyone with the RA150 service manual who could verify R401/402 values ?
is it possible to find the RA150 service manual online ?

C401 220uF 25V cap was blown, replaced ... C402 ok, very low esr ok, 224uF ok, leakage don't know, have nothing to measure it ...
all caps on this amp are cheap bottom of the line 4th grade chinese Jun Fu ...
considering replacing them all, but first want to find the source of the problem ...

thanks in advance ... hope this discussion helps others as well, the utub videos on repairing the ra150 show nothing ...

[solartony]

hi km6xz,
could you plz post the ra150 service manual ?
C401/2 show 1000uF/35V on the ra500 diagram, but are 220uf/25v on the ra150 pcb,
the two power supplies are different...

plz read my post below w/ more details ...
thx in advance

[solartony]

hi docSanchez,
why switch to a 24vdc relay instead of the 12vdc ?

thx in advance

[solartony]

ra-150 does not power up

hi all,
the plot thickens ...

on the top right side of the power supply pcb, to the right of the relay:
ra500pwr v1.1 00.10.04 (dec 2004 ? build date)

so, is it indeed a ra-150 w/ a ra-500 pwr supply ?
but why the mismatches from the diagram (see my previous post) ?

btw, no amount of shakin', hitting the relay does nothing, still 4 sec after power on and ... the clip of death ... led's out ...

thx in advance

[g1]

Does this help?
http://bee.mif.pg.gda.pl/ciasteczkow...s_ra150_sm.pdf

[solartony]

hi all,
Z1 comes to 10vdc, a bit less when relay clips at 4 secs... that's low !
Z2 comes to -15vdc, a bit over, stays there when relay clips ...

D401 has 68vac in pins, and 90vdc out ... how can that be ?


many thx to all in advance

[solartony]

terrific, yes it does help, the world is starting to come to its senses,
at least according to the diagram designers ...

thx g1, much appreciated ...

C403/4 220uF for the posts before, that makes more sense ... C403 replaced w/ a rubycon, was blown up ...

plz see previous post w/ some samples on z1,2 and d401 ...

many thx in advance

[solartony]

that blown up C403 did some damage for sure ...
checking other stuff down the line ... r403 ...

many thx in advance

[Enzo]

So either Z1 zener is failing or something is loading down the +15.

I don't see D401. But if it is a power supply, 68vDC rectifies and filters to about 96v, less some diode drops.


Sorry, typo: I meant 68vAC

[solartony]

thx Enzo, much appreciated ...

the other way around 68 alternate in, 90 continuous out ... !!
less in, more out ...

d401 is the rectifying bridge upfront out of the pwr pcb,
screwed to the bottom metal case serving as a heat sink ..

yes, i agree, replacing z1 as soon as i can get to the shop ...
may very well be the case, something down the line is pulling z1 down i suspect too,
b/c r401/c403 get hot, very ....
but so do the other -15vdc on the other side, a bit less hot it seems ..
what could be draining z1 ?

many thx in advance

[Enzo]

AC voltage is measured in RMS. The voltage on your meter is that. But the actual voltage goes to a peak voltage much higher. When you rectify that, and add a filter cap, the cap charges to the peak voltage of the AC, not the RMS. You lose a couple volts in the circuit, but essentially you multiply the AC voltage by 1.414, and you get the DC your circuit will charge to. I wrote 68DC, and that was a typo, I meant to write 68AC, which you provided.

So, 68vAC in and expect 90vDC or so.

[solartony]

terrific, thx Enzo, you are absolutely right, much appreciated ...

the pcb areas around the zeners and r401/2 are dark, not
carbon, leads are oxidized dark on both, the resistor paint has fallen off ...

r403/4 look pristine, no burning/oxidation, the others components
on the entire pwr pcb are in fairly good shape, no burning/oxidation to see ...

many thx in advance