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Marantz 1090 right side fuse blows

ecluser..."do you have +38V at the emitter of Q803?" Yes I do.I took the temp there several times and came up with 37.2.Enough right?
 
So if I get 37.2 on the emitter of Q803 as per the schematic does that mean that Q803 is still good and not shorted out?
I'm not sure where to find the speaker fuse.
There are three fuses in there.
One .5a 250volt and then the two 5a 250 volts.
Being a .5a does that indicate its the speaker fuse?
 
Since I don't know what a speaker fuse is I checked the voltage at the terminals of speaker systems 1 & 2 from the inside.Not the outside where the speaker wire connects.I got .18 and .2 on speaker 1 L&R respectively and .04-.03 on speaker 2 L&R.
Sounds good?
What does it mean?
 
I will try to answer your questions.

From your very first post...
gyrene said:
Had the power up for less than two minutes I'd say and the fuse on the right side popped.Its a 250v 5a.
Its the fuse on the main amp board F702
Click to expand...

Since you made a direct reference to the part identification (F702), and this fuse is indeed a 5A/250V fuse, it should be one of the speaker fuses.

There is a 3.5A fuse (F001) on the primary side of the power transformer, fuse F802 is good since you have +38V at the emitter of Q803 (yes, 37.2V is close enough and this part of the circuit seems correct).

It seems to me that you may have a problem with the speaker switch or a short at the speaker connectors. Sometimes a very small wire from multi strand speaker wires can stay inside the connector and it may make a short with the steel chassis. Look closely.

You should have the same voltage on speaker 1 and speaker 2, unless the speaker switch is bad.

With the speaker switches disengaged, do you have a good sound with headphones (alone)? It would be encouraging to know that.
 
ecluser..."Oh crap" I knew I should not have gotten rid of those headphones back in 1985! Darn.
No headphones sorry.
I just checked the voltage across F701=-1.4v and F702=-43.7v

It has been F702 that blows when the speakers are engaged.
How can I check the speaker switch?
 
ecluser I just noticed that this amp does not have a jumper in the preout like my other amp does.
Significant?
The preout main in is empty.
 

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You don't need jumper on this amp. Like many Marantz they have short pins inside the Main In jacks and the pins make the contact when there is no external plugs connected to the jacks.

At -44V on F702, you have a major problem on this side. And -1.4V is not so good too.

On the F702 side, remove the power transistors Q722 and Q724, and take a new DC voltage measurment. This is probably Q724 which is shorted between C and E.
 
I will get Q724 out and tested today.
If its dead what would a suitable replacement be?
While checking specs and trying to match them to current Q's what is the most important spec to match? Power Disipation? Collector Current?Vceo?Vcbo?
Expecting to not be able to get a one to one match.And of course where?
Did some looking last night for replacement Q's in case they are needed and man I gotta say...makes my head spin.
 
gyrene said:
I will get Q724 out and tested today.
Click to expand...

Remove Q722 also. I want to know if you have a correct DC voltage at the output (fuse terminal), on that channel, without power transistors.

gyrene said:
If its dead what would a suitable replacement be?
While checking specs and trying to match them to current Q's what is the most important spec to match? Power Disipation? Collector Current?Vceo?Vcbo?
Click to expand...

Vceo, Ic, Pd, hFE

gyrene said:
Expecting to not be able to get a one to one match.And of course where?
Did some looking last night for replacement Q's in case they are needed and man I gotta say...makes my head spin.
Click to expand...

I am sure somes will make suggestions for the replacements.

Don't place any order at this moment, you will probably need to replace a few capacitors and small signal transistors.

Can you measure hFE with your meter?
 
I got Q724 out and recorded the following measurements.Its a PNP
Red to base and black to collector =O.L.
Red to base and black to emmiter= O.L.
It being a PNP those readings are good,right?

I will get Q722 out next and report back shortly.
I don't think my meter does hFE.It has a Freq mode but thats not the right one,is it?
 
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Q722 is out and tested this way.Its an NPN.
Red to base black to collector=.475
Red to base black to emitter =.482
This being an NPN this one is looking good too?
 
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ecluser thank you for your help.
As for checking DC voltage at the output...please keep it simple,again, so I can follow.
Thank you

I checked these reading a few times today because I didn't trust my sequencing.But I feel pretty sure I have the correct numbers up.
If it looks flaky to anyone or if you want me to do a re test just give me the word.
Thanks
 
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Your testing procedure is incomplete. You must also test between C and E. You must have O.L. in both directions. If the transistor is shorted between C and E, you will have a very low reading.

Always test in both directions between each pair of terminal. This is just 6 measurements per transistor, not a big job. Also, for the PNP, when the black probe is connected to the base you should have ~ 0.6V

To summarize: Between B-C and B-E, ~0.6V in one direction and O.L. in the other direction. The direction of conduction tells you if this is a PNP (black on base) or a NPN (red on base). Between C-E, should test O.L. in both directions.

For the DC voltage at the output, just like you did before. I prefer that you take the measurement directly at the speaker fuse (red probe), with the speaker switch to OFF, to rule out possible problems with the speaker switch. The black probe on the chassis.
 
Outstanding ecluser.
Thank you very much for your help.

Update: Q722 C to E =O.L.
Q724 C to E=0.000
D.C.voltage at the fuse is .09 on F702 and 00.00 on F701
 
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Did some looking at digikey and it makes for a confusing time for sure.
If I get the Pd right then the Ic is not quite right and it continues like that.
I'll have to wait for someone with more experience and knowledge to show me how to choose or point out a good choice of replacement transistor.
 
Cant help with the 2sd588, but the PNP (q723 and Q724) 2SB618 are available at MAT electronics for about $3.50 a pop (no pun intended) 800.628.1118
 
Dang Chief thanks for the headsup on that.Really appreciate it.I didn't even know mat electronics existed.Thank you.
 
Even though Q724 is no good I still have to find out what killed it.
Its magnifying glass time I guess.
If its the speakers switch what would I see upon closer inspection thats causing the short?
Spiders? Dust? Corrosion?
 
I tried to isolate the speaker switch by doing a continuity check from the posts on the switch to the speaker connection on the inboard side of the rear panel.Seems o.k. there.
My attention is drawn back to that dog of a capacitor at C804 which looks rusted on top.But in looking at the schematic I can't follow the electron flow from C804 to the blown fuse.And I remember that the heat sink on Q803, I think it was, looked like it had been sitting right across the two adjacent resistors.But of course now I can't be sure having moved the heat sink out of the way a week ago.
I'll remove C804 and see how it tests out.
If thats dead what then?
 
O.K. maybe I should have remembered checking capacitance ain't really that doable...
oh well CRS is part of the aging process I guess.
 
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