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Marantz 1090 - Is she too far gone?

I just watched a video of a C64 which had been left in the weather for a dozen years with pine needles INSIDE it and rat crap.. turned on and worked with minimal work.. A marantz should handle some dust and rust in stride :D
 
Mike Sweeney said:
I just watched a video of a C64 which had been left in the weather for a dozen years with pine needles INSIDE it and rat crap.. turned on and worked with minimal work.. A marantz should handle some dust and rust in stride :D
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Thanks for the vote of confidence Mike. I need all I can get. Do you have any advice on post repair start-up procedures? Anything I should try before firing her up?
 
Good scrub of contacts, this includes things like the fuse holder etc. Remove the fuse and put one about 1/2 the rating in it's place. The fuse is meant to protect the unit against max draw.. for example the 2245 on the bench has a 3 amp fuse. .but in reality, draws about 1/2 amp.. a bit more on the initial inrush but nothing near 3 amps. If I'm going to pop a fuse on something new, I want to pop as early as possible. So around 1 amp is the ball park. Fuses are cheap. Dim bulb tester is useful to keep it from frying. I use a "killawatt" reader to see the voltage and amp draw.. it's cheap and works. My personal preference is to replace the main filter caps before anything else is done. I'm not keeping them anyways.. so that clears the power to the power supply board. Often I'll rebuild the PS board too if it looks intact and not crispy. That gives me a solid base to work with. My newest habit on units like the 2230/2245 I've got is to disconnect and pull the main amps out. That leaves the tone, pre-amp and phono amp in place and I can see if the protection circuit works. If protection works, I will jumper in one of the channels and test. Then the other and test. I'm a big fan of divide and conquer. Again, I've taken to pulling the boards out anyways for rework and rewiring of the chassis so for me, it makes sense to go ahead and pull them before smoke testing. Make sure to cover the ends of dangling wires :o shorts are not your friend. I use the blue painters tape.. no residue and it's pretty cheap and stands out visually.. I found this on amazon and I might get it.. I love color coding. .I match my jumpers to the color of the wires I'm working on. red to red, black to black and so on. when you have a rats nest of jumpers it helps.
https://www.amazon.com/Colored-Masking-Tape-6-PACK-Variety/dp/B0741S21B3/
 
Hartin said:
Thanks for the vote of confidence Mike. I need all I can get. Do you have any advice on post repair start-up procedures? Anything I should try before firing her up?
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A dim bulb tester is the standard procedure here. If you're not familiar, there are many guides on AK. An incandescent bulb in series with the power input--serves as a current limiter. You start the rebuilt component plugged into the DBT. Normal operation, the light will go bright for a sec as the power caps fill, then go dim as the component sits at idle state. If it stays bright, theres a current draw and you unplug and try again. Without having blown transistors.

As someone advised me "You never need a DBT until you did."

After that test is passed, measure DC offset on speaker outputs with DMM before risking speakers.
 
Hartin said:
Here's the repaired main amp board. Had a little trouble with pads lifting in previously repaired areas but otherwise no issues.

Im going to put it back together and see if it will fire up. Any tips? Should I try headphones first? Connect up to sacrificial speakers? Measure speaker output with a DMM?
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Woah I'd replace those trimmers first, they're known to be corroded and blow up outputs. And the burnt to heck resistor next to the white 5W one in the top right. Maybe even caps while you're in there as they may have seen some wild current or voltage when things went down.
 
ivandezande said:
Woah I'd replace those trimmers first, they're known to be corroded and blow up outputs. And the burnt to heck resistor next to the white 5W one in the top right. Maybe even caps while you're in there as they may have seen some wild current or voltage when things went down.
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Good catch. I actually ordered the trimpots and forgot to swap them out. Also good catch on that resistor. It measured within spec but upon visual comparison to other 1090's its definitely changed colors. Is there any way to test the unit out without blowing the output transformers (in addition to the dim bulb)? Perhaps remove them for testing? I'd rather not have to source those again if possible so I'd like to take all reasonable steps to protect them.
 
Hartin said:
Good catch. I actually ordered the trimpots and forgot to swap them out. Also good catch on that resistor. It measured within spec but upon visual comparison to other 1090's its definitely changed colors. Is there any way to test the unit out without blowing the output transformers (in addition to the dim bulb)? Perhaps remove them for testing? I'd rather not have to source those again if possible so I'd like to take all reasonable steps to protect them.
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Yup you should be good running it without the output transistors installed, however, the DBT will protect them. Your call, I totally get being extra careful.
 
I have a 1090 myself. I love mine. Sound fantastic and looks great. I also had issues when I first got mine. I am not a tech so I had a pro do the work. My left channel was also out. Left fuse was also blown. Right one was ok. He recapped both channels so they were equal. Something on the boards was the course of the blown fuse. I did not have to give much money for the 1090. Under 100 bucks to start and just over 100 bucks to fix. The 1090 is a rare one. But parts for it are interchangeable with other unit so I was told by the tech. So there is that. Cosmetically mine was super.
Do this. Go out to the net and try to find one. I know of one on Epray that's been there forever that's missing stuff but that's it. Every once in a blue moon you may see one oversee's at high money. So yes it's worth the refurbishing in my opinion. I did.15445593883005318237079288645983.jpg
 
OK She seems to have passed the dim bulb test. Creating that device was fairly simple. I used a 60W incandescent bulb in series. When I turned the amp on the light flashed bright and dimmed quickly then went out.

I've replaced the fuses brought her up for a test run on headphones. I'm getting sound there. I guess its time to put the outputs back in and check the DC offset.

I'm trying to find a good tutorial on how to test the DC offset. I've gathered that I'm measuring the DC voltage between the + and - speaker terminals on each channel. Should I have the volume up or down? Do I need some load across those terminals as well?
 
Well scratch all that. I put the outputs back in and powered up on the dim bulb. This time the bulb stayed bright and the left channel smoked. Burned up a few resistors in a matter of seconds. Guess im back to the drawing board and way in over my head with this one.
 
So with the outputs removed, your headphones sounded OK? Did you use mica to insulate the transistors from the heatsink? Was the bias adjustment turned down? If that was turned up, it would pop the outputs and cause a short.
 
redk9258 said:
So with the outputs removed, your headphones sounded OK? Did you use mica to insulate the transistors from the heatsink? Was the bias adjustment turned down? If that was turned up, it would pop the outputs and cause a short.
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Headphones did sound OK.
I didnt have the heatsink installed.
I dont clearly understand the relationship between the bias adjustment and the DC offset.
I did find a tutorial to measure the DC offset and I did that.
Not sure how to measure the bias though.
Not having a frame of reference I measureed the resistance of thr trim pots as they came. They were both around 200 ohm.

Guess I need to test the outputs again to see if they were shorted.
 
Would having the service manual help you out? If so, I have one that my tech used to fix mine 1090. It's to big for me to open post it here. You will need to send me your email and I can send it to you. Check my profile page.
 
Wolfman181 said:
Would having the service manual help you out? If so, I have one that my tech used to fix mine 1090. It's to big for me to open post it here. You will need to send me your email and I can send it to you. Check my profile page.
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I appreciate the offer Wolfman. I've downloaded a copy of the SM. The service manual has a section for "Adjustment of Idling Current" that goes like this:
Connect a vacuum voltmeter to between emitters Q721 and Q723. Adjust R771 until 12mA is reached. Likewise, adjust Q724, Q722 and R772

This is what I was attempting to do when the unit smoked.

Unfortunately, the problem lies with me. I'm really too green and I've had to make some assumptions that seem to be incorrect.
 
Hartin said:
I appreciate the offer Wolfman. I've downloaded a copy of the SM. The service manual has a section for "Adjustment of Idling Current" that goes like this:
Connect a vacuum voltmeter to between emitters Q721 and Q723. Adjust R771 until 12mA is reached. Likewise, adjust Q724, Q722 and R772

This is what I was attempting to do when the unit smoked.

Unfortunately, the problem lies with me. I'm really too green and I've had to make some assumptions that seem to be incorrect.
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Something is still amiss. The bias should be able to be full blast on DBT and nothing bad will happen like things smoking.
How do I know? I've done it.

Bias - constant current running through the output transistors, measured usually at the emitter resistor.
DC offset - measured at the speaker terminals, adjustable, or when not it is controlled by how well the input pair is matched in gain.
 
ivandezande said:
Something is still amiss. The bias should be able to be full blast on DBT and nothing bad will happen like things smoking.
How do I know? I've done it.

Bias - constant current running through the output transistors, measured usually at the emitter resistor.
DC offset - measured at the speaker terminals, adjustable, or when not it is controlled by how well the input pair is matched in gain.
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I agree, something is definitely amiss. I've ordered new output transistors and they should be here next week. In the meantime I'm going to start replacing the caps in the power amp board just to be safe.

Should I pull the smaller transistors from circuit and test those as well?
 
Hartin said:
I agree, something is definitely amiss. I've ordered new output transistors and they should be here next week. In the meantime I'm going to start replacing the caps in the power amp board just to be safe.

Should I pull the smaller transistors from circuit and test those as well?
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For sure. You don't even need to pull them, a short will appear in circuit.
 
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