Rotel RB 990BX -- no output from left channel.

Mystery

Just got it and no output from left channel.
Hopefully, it's just the fuse.
Will update...

SCompRacer

One other thing to check. The RCA input blocks are secured to rear panel with screw. The RCA block is soldered to the circuit boards attached to side heat sinks. I've had one that was abused in shipping and the RCA block broke away from the board. Like dropped on one corner and the chassis twisted. It was actually a RB-985 five channel amp but the RCA blocks attach the same way as the RB-990BX.

Mystery

RCA posts are fine.
I didn't see fuses in there but there are two pretty brown components on the right channel that's not working.
Here are pics:

Mystery

Found the fuses and one of them on the right side is blown.
Hopefully, it's that fuse but even then the burnt components are alarming.
Will run to the radioshack tomorrow for the fuses.

zane77

Can't really tell what those are, possibly so,e kind of op-amp with a heat sink??

drummer86

I have a digital version of the service manual if you need it. Just shoot me a PM with your email address.

Mystery

I have the service manual from this link: http://bwgroupsupport.com/downloads/techmanuals/rotel/RB-990BX-TM.pdf
Blown is 5mf 6A 125V.
However, part list in the schematics mention one is 6A and another is 6.3A but the schematics diagram mention all as 6.3A.
Also, no idea about the correct voltage. I'll go with 250v.

Mystery

BTW, I took the fuse from left channel and put it in the blown one and now that channel works so I guess it's just the fuse.
Should I replace just that one with 6A or replace all of them with 6.3A 125v or 250v?

Mystery

Well that's the confusion.
If you look at the schematics, parts for fuse 601 is 6A and 603 is 6.3A but if you look at diagram in the same schematics, both are 6.3A.
All 4 existing fuses in the amp are 6A so I guess I'll just get 6A and see how long that holds.

megasat16

You are absolutely fine to use the 6A fuse instead of the 6.3A fuse.

One thing you need to make sure is the voltage rating of the fuse that you need and the type (fast acting or slow blow or ceramic).

Check the User Manual to see if it mentioned the type and the voltage?

Mystery

User and service manual don't say what type nor voltage.
All they have is ampere with warning to replace with similar type fuse.
Usually amps use fast flow fuse.
Online search mention it uses slow blow but some say fast so need to check it again.
Once it starts working normally, it'll be interesting to compare with Adcom GFA-555II as they have same power ratings.

As you see below, it's either 6A and 6.3A per parts list and both 6.3A per diagram:

megasat16

Ok! Check the markings on the fuse that came out of the amp. It should say the voltage as well as the amp.

What does it look like?

F6A = Fast Acting 6 Amp
T6.3A = Timed (Slow Blow) 6.3Amp. You can use 6A Slow Blow Type.

You need to get Two Different 6A Types for different fuse locations.

Mystery

Yes, if I go by parts list, I need F6A and T6.3A but if I go by schematics diagram, it shows both as T6.3A for FU601 and FU603.
FU601 is the one that's blown.
Hmm...

Edit: I checked all the fuses and right channel has 5mf 6A/125v. One of them is blown.
Left has F 6A/125v on both fuses.
So the left has fast 6A/125v and right has 5mf 6A/125v. Does mf mean it's slow blow, may be 5 milli something?

Also, there is a sticker with 6A/125v next to each fuse on the amp itself so all I need is 6A for all four. Now just to make sure fast or slow blow.

megasat16

I see that's some confusion.

I think CEE means the country in the Central and Eastern Europe. These countries uses Timed 6.3A fuse.

For US and Canada which I think has STD designation uses the F6A fuses.

This probably has to do with the Voltage and the different fuse ratings these European Countries use.

So, you can use 6A Fast Acting for all 4 fuses.

megasat16

5MF probably means the part number or the company that came from.

But you need to use 6A fast acting at 125V rating fuses.

RatShack probably don't have the 125V fuses. If they only has 250V fuses, use the 250V,3A fast acting fuse.

Mystery

megasat16 wrote: »

I see that's some confusion.
I think CEE means the country in the Central and Eastern Europe. These countries uses Timed 6.3A fuse.
For US and Canada which I think has STD designation uses the F6A fuses.
This probably has to do with the Voltage and the different fuse ratings these European Countries use.
So, you can use 6A Fast Acting for all 4 fuses.

That's what I'm thinking as that channel worked when I swapped the fuse from other side, it should be fine.

I'll try fast 6A and see if I smell smoke or not.
thanks

Mystery

It's working fine with a 6A 125v fast blow fuse.
DC offset is exactly at 7mv as recommended in the schematics so that's great.

Should I be worried about that amber/brown component most likely by overheating?
thanks

megasat16

You fixed it! Congrats!

That amber / brown stuff in the picture seems to be some kind of glue (same stuff you see underneath the caps).

I think it is some kind of contact cement to make sure the components stay in place but that stuff changed the color overtime from yellowish to brownish (due to heat and just aging).

I wouldn't worry about it but I wouldn't crank up the amp too loud for the regular use for at least a few days. Just use the amp at low listening levels in the first 3-4 days for at least a few hours a day before you crank it up too loud.

Mystery

Thanks.
I hope that's just color of heated glue and not overheated part.
It's been working so far for last two days so hopefully it'll hold on.
I'm liking it better than Adcom GFA-555II.

drummer86

Mystery wrote: »

I'm liking it better than Adcom GFA-555II.

I was wondering about that. I like my 990 but have always wondered how it stacked up against other "budget" 200wpc amps. For the money I have in mine I doubt I could have done much better.

Dabutcher

I have the same amp . Paid $22.99 without being able to test it other than light on after plugging it in. One side was out when I got it home. Replaced fuse that was bad and it worked all summer. Gets pretty hot ? But I guess that's normal? I keep the cover off for ventilation. Never compared it to my adcom 555? Maybe some day. Good luck. D

Mystery

It hasn't run too hot but I'm think it'll run hotter than Adcom as the cabinet is almost half the height of Adcom so not a whole lot of room inside for air circulation but is much deeper so not sure.

lanchile

Mystery wrote: »

It hasn't run too hot but I'm think it'll run hotter than Adcom as the cabinet is almost half the height of Adcom so not a whole lot of room inside for air circulation but is much deeper so not sure.

\

Check bias!