DBX RTA-1 - repair and restoration

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NOON

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Hi everyone! I just picked up a DBX RTA-1 real time analyzer for cheap. I can find very little about these online apart from that they were very well regarded. Mine is missing top and bottom of case and a few button caps but otherwise looks intact.

Very interesting beastie, it's based on a standard 8088 PC motherboard with 8 x 8bit ISA slots. It's got a built-in CRT, several ISA cards and a couple of other custom cards. The three 'digital' cards are a VGA card, what looks like a serial card with a couple of 16550 UART chips and a custom card that seems to have the RTC (real-time clock) and a bit of interconnecting logic between systems (e.g. VGA card and built-in monitor). There's an empty slot marked 'printer' on the back that I assume used to house a parallel port card.

Two other full length ISA cards have loads of analogue circuitry involving lots of DBX VCAs among other things. The sections are marked with frequencies so I assume these are the analogue filters. There's a big board attached to one side of the case that appears to serve the mic ins on the front and the analogue outs on the back. There's another small board that attaches to the power supply that has power out connections to the various sections as well as a small bit of circuitry that includes a 555 and a regulator, so I assume some kind of charge pump for the phantom power.

The switchmode power supply was hanging loose in the case (luckily didn't break the CRT during shipping!). Even though the back of the case has a 115/230V switch, it's been disconnected internally and the PSU has a big sticker saying 115V, even though it looks original to the chassis. Unfortunately I'm in a 230V country.

As far as I can tell from a good look around inside everything is there, all the cables seem obvious were they go with no mysteries and I can't see any evidence of smoke escaping, corrosion or other damage. Basically about as good as you can hope for with something of this age and unknown provenance.

I worked in IT in the 90s so I've got some familiarity with working on PCs of this vintage, although not so much with restoration of them when they're more than 30 years old! I'm sure the internet will be full of vintage computer nerds with tips though, the real problem is going to be the custom stuff.

I can't even find a user manual for these things let alone schematics or a service manual. I've emailed DBX, a local dealer and a guy who came up in a search as having done some software development for these back in the day but haven't heard back yet. I'm hoping someone here has some information stored away somewhere in their archives or memories on these things.
 

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NOON

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Here's a picture of the PSU and label. Anyone familiar with these and how to set/modify them to 230V? Switchmode PSUs are a bit of a gap in my knowledge, I consider them magic boxes with danger inside.
 

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NOON

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And a couple more shots for context..
 

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NOON

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I've since discovered that the technology was sold on and continued as the Sound Technology RTA 4000. They're still in business and I've emailed requesting support info. Does this unit ring any bells with anyone?
 

moamps

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Here's a picture of the PSU and label. Anyone familiar with these and how to set/modify them to 230V? Switchmode PSUs are a bit of a gap in my knowledge, I consider them magic boxes with danger inside.
According to the labels on the power supply, it is a universal power supply that does not need to be adjusted to operate at 230V, IMHO.

1637169573114.png
 

NOON

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According to the labels on the power supply, it is a universal power supply that does not need to be adjusted to operate at 230V, IMHO.

I saw that label as well and thought it may be universal but I'm suspicious of the big red label on the side saying 115V. I'll have a look at the input circuits and compare to the diagram from abbey then try powering it up on my variac out of the chassis to see if any smoke comes out. Then I'll proceed to powering up the rest section by section, carefully checking and possibly replacing power rail tantalums and electrolytics first.

I've had an email reply from a very generous person who still services these units in the US and I now have a copy of the user manual with the promise of more. I've asked permission to upload to the docs section here.
 

NOON

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DBX made some claims about the quality of their pink noise generators and their bandpass filters in the user's manual, you can check out the schematics for yourself if you're interested.
 

Disco Volante

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Aahh pure nostalgia of a PC motherboard. Seems to be lots of room for increasing the memory on that thing, maybe up to 640kB!?. I remember scavenging those little 16pin RAM chips from scrapped hardware to upgrade my own, way back when computers were expensive... Probably someone sells those for real money on Fleabay these days..

Wonder what OS that thing has?

Great find, have fun!
 

NOON

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I was thinking how easy it would be to max out the RAM, add some storage etc to this thing, but it's running custom code from a ROM and it likely would make zero difference, possibly even mess it up.
 

NOON

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A closer look at the power supply reveals the board is a substitute into that frame and doesn't match the label on the side. New mounting holes drilled and some others that don't match up. It doesn't have specs and pinout for outputs so I'll have to check that but much more confident it'll work at 240v now.
 

Whoops

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From that Abbey diagram it seems the different would just be inserting one Jumper, but as your pcb might be retrofited after it's hard to know...
 
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