Proton 930 Service Manual ???

[Guest The man who fell to earth]

I found this Proton 930 from the year 1981 for a bargain. (photos attached because we all love photos.)

I know she is nothing special.

As with all theses Protons (NADs) it has issues with crystal display, fm tuner selection etc, but is for the most part o.k. 

There's a few scorched (brownish patches on the pcb), no bulging caps, someone has been in here many times, some dodgy soldering, Thermal paste everywhere...

I have been practicing my soldering and doing my best to learn about electronics and have had success reviving some junk finds from garage sales etc.

I'd like to change the caps in her, but cannot for the life of me find a service manual online (for under $30) to adjust bias (a friend said I needed to replace resistors to adjust bias, but I don't believe so) I see bias adjustment trim pots, but no test points ?

This Proton 930 sounds nice, but not as good as people say the NAD 3020 is and that the Proton should. S
he runs very hot without being pushed, so would suspect high bias if anything? 

Seems the trim pots have original loctite stuff on them (or maybe not original)

The DC offset measures almost zero on both channels, and the channels sound even to my ear, but I would love to find a service manual or advice on specs and procedure (test points) for bias at the least. 

I have ordered from mouser and will enjoy my first ever full recap (successful or not). 

 

[Wimbo]

I'm using the power amp of one of these driving a passive sub. Runs well. No display though hehe

[Zaphod Beeblebrox]

Proton was/is manufactured by a company called Fullett (sp?). Fullett used to manufacture NAD products. When Fullett and NAD fell out, Fullett continued manufacturing NAD, but with the Proton brand name. Early Proton products can be serviced by using the appropriate NAD service manual. Even the part designations are identical. An NAD 7140 service manual should, as I best recall, be the appropriate match for your Proton. Your friend is correct. Trim pots on early NADs and Protons were notorious for falling apart, when adjustment was attempted. They should be replaced. Measuring bias current across the emitters of the output devices is probably the simplest method of setting bias current. Don't forget: Replace the bias pots BEFORE attempting adjustment. They will fall apart. 

 

As for the messy soldering and thermal paste, well, that sounds pretty normal for the product. Fullett were not well regarded for high standards of build quality. Which is probably why NAD gave them the flick. 

Edited December 8, 2018 by Zaphod Beeblebrox

[Guest The man who fell to earth]

Thank you Zaphod Beeblebrox for what is, without a doubt, the most 'On Point' reply I have ever had on a forum query ever.

I did know about the Fullet /Nad history, but was not at all sure which NAD manual would correspond to the 930 (your breadth of knowledge is astounding, and your generosity in taking time to reply and help so many people is wonderful.)

Thanks for heads up on the trim pots being dodgy for certain, and for the notion that it may not have been played with (as yet) by an amateur, but may have actually left the factory with evidence of sloppy workmanship (not sure how to feel about that?) Ta!

[cmc]

Reviving an old post i know but i recently pulled my old 930 out of the cupboard where it had been languishing for years.  Unfortunately, seems to have died from neglect in the interim i.e. plug it in and no response.  After reading Zaphod Beeblebrox post i wonder whether that is the natural way of things but the optimist/nostalgist in me wants to see if it can be revived.  I will take it to my local tech tomorrow to see if any signs of life can be found.  Pictures above could be from mine except for the missing dust.  i really liked it in its day.