1090 Basket Case

[Richs_Trains]

Okay, so I bought a 1090 on craigslist for $50.00 to use for parts for a 1090 that I recapped. This unit was filthy inside and someone had pulled 1 output transistor from each channel, a 588 on one side and a 618 on the other. I was just going to take the cosmetic parts I need and trash the rest, but I just couldn't do it. I had bought some transistors from China and was advised here that they are probably fake, so I didn't use them in the 1090 I recapped, but thought I would throw them in this one and see what happens. Firstly, whoever pulled the old transistors used the heat and rip method and did not remove the old solder before removing the chips, so the board and the foils are a mess, also there are several spots where they did work and burned off the foils. I jumped with wire all that I could find, installed the new (China) transistors and used a dim bulb to test. No light, no fire, so I went for real power and connected a tuner and speakers. I get sound, very poor and very distorted and I get no reading across output transistor emitters for mA and should be around 12. Are my bias transistors shot or are the China outputs garbage and just I'm hearing the headphone amp out the speakers? Should I keep trying or is this a unit for the scrap heap (I hate to trash any Marantz). Thanks for your help and advise.

 

[rBuckner]

It's impossible to know what may be wrong. I'd guess someone who knew enough to be dangerous, who maybe knew nothing, thought they'd try to fix it. I'm guessing the outputs were removed and probably were found to be okay so they gave up, probably as no YouTube video on how to fix a Marantz 1090 was to be found! Perhaps if you've harvested what you want there may be some other parts worth eBay-ing out?

The schematic in the SM has voltages on the amp section, measure those and see if you can see where the problem lies or post those voltages and we'll have a crack at it! Have you connected the preamp outs to another amp to see if that is okay? Checked power supply voltages?

 

[Richs_Trains]

I am borderline enough knowledge to be dangerous, I think I will harvest a few more parts and then keep it around for switches and the like. My question now, the 1090 I recapped had no tone control when I started and under advice of the site I replaced the drivers on the tone board (I think QE-01 - QE08, this gave me tone in and out on both channels, but I still have no noticeable 'loudness' control. The basket case (as bad as it is) has a functional loudness circuit (even with the distorted signal, you can clearly hear the loudness kick in), I would like to just switch out the tone board, but this set up as multiple circuit functions on each board and doing that would probably introduce bad stuff to the working amp. What components are part of the loudness circuit and which would you suggest I test/replace from the basket case first? Listening to the 1090, it almost sounds like the 'loudness' is always on when the tone control is on (I have to turn down the bass and mid below flat), I don't know if that observation makes a difference. Thanks for the help. Rich

 

[rBuckner]

It could be the loudness switch is stuck on, have you done a DeOxit treatment? I'd avoid swapping boards if it was me!

 

[petehall347]

it is mv you want to be reading not ma .

 

[Richs_Trains]

I did deoxit on all the controls on the 'good' amp, I believe the contacts for this control are a slide type switch that is PC mounted, that's where I cleaned. I was hoping not to swap boards, but maybe some of the components that make up the loudness circuit. The tone board has ribbon connectors that I have read are not fun to swap out and prone to failure.

 

[Richs_Trains]

OK, still playing with this 1090 while I wait for the caps for my 4070 to come in. I measured idle current and the right channel was racing up to 40+, so I turned it off, got ready and powered up, adjusted it to a pretty steady 12 mv and went to the left channel. The left channel has .3 mv and will not change with adjusting. Where to next?

 

[drew_t]

^ I posted a few days ago looking for advice on biasing a 1090 and didn't get any response. I found a thread on the diyaudio forum that is somewhat long and meandering, but may be of some use to you in trying to troubleshoot yours. Link

 

[Richs_Trains]

From what I understand, there is no bias adjustment on the 1090, just the idle current trimmers. The drivers on the outside of the output transistors are the bias generators.