dbx 4bx repair options

[KISS]

Bypass is stuck on. Problem was once intermittant and then became continuous. cycle power by pulling plug and it's still in bypass. Doesn't appear to be the button.

I tried a long time ago to fix it with no luck.

I do have prints. Large prints. No service docs.

Has anybody had the problem? What was the fix. Does anybody know anybody that might tackle the repair in the US.

[XEAGLEKEEPER]

Is it a mechanical or electronic switch.Could you send me a copy of the schematic?
Thanks
Dave

[KISS]

The prints I have are Japanease, dbx and Kyocera blue prints in sizes ranging from 8.5x11, 11 x 17, 17 x 24 and maybe slightly bigger They all show slightly different informatiion. I have a parts placement diagram that has notes in Japanease. Some are CAD on white paper and some are real blue prints. I tried a camera set at 5 MP, manual focus and converted to a pdf and it wasn't readable. I'll try 12 MP and see what I get.

I'd probably have to resort to snail mail if your REALLY interested in helping. e.g. figure out how it's supposed to work.

I just figured out that the front panel uses in IR encoder (SAB3021) chip to encode the push buttons and an IR decoder (SAB3023) chip to decode them without using an IR LED to pass button information from the front panel to the motherboard.

a 4053 FF is used to drive the LED's in a very odd configuration.

My digital background is very good because in the mid 70's I designed a microprogrammed hardware sorter with Small Scale integration IC's and I even desiged and built a crane controller for a model railroad which would load and unload 27 pieces of cargo to a loading dock with a push of a button. The first model's program was hand assembled (compiled). The latter model was single board computer (BASIC) based. The IBM PC was just making it's debut at the time of the crane and I didn't own one. PCB layouts had to be "Taped".

The PC didn't exist with the sorter project. The designed microcode was 16 bits wide and 16 long. It could sort ascending and decending depending on the microcode.

The cargo was on three rows of 3 boxcars. I also modified a Blaupunkt car radio so that it would support seek. That was all CMOS stuff.

[XEAGLEKEEPER]

just figured out that the front panel uses in IR encoder (SAB3021) chip to encode the push buttons and an IR decoder (SAB3023) chip to decode them without using an IR LED to pass button information from the front panel to the motherboard.

a 4053 FF is used to drive the LED's in a very odd configuration.

Do you have a logic probe or o'scope to monitor encoder output?A faulty solder connection in this area wouldn't be out of the question.If Problem was once intermittant and then became continuous.

Dave

[KISS]

I have a scope, but I don't understand the circuit or what's supposed to happen. The data sheets for the SAB parts would help emensely.

I checked all of the solder connections.

The camera method for capturing the schematic doesn't work. I'll have to try to scan them at work and email them to you.

That unit is an incredible piece of work. An aside: So is the Carver TX1-11 Asymetrical Charged Coupled Decoder for FM multipath reduction. I've heard that I probably own the best tuner ever made. The Technics Professional ST-9030.

[XEAGLEKEEPER]

So is the Carver TX1-11 Asymetrical Charged Coupled Decoder for FM multipath reduction .................. I'll bet you can say that three times in a row quickly

I have a DBX 224 for my TEAC 3300S probably simple in comparison.

Probably going to have to break the circuit down gate by gate. Do you remember your truth tables? I do! I dealt with it daily working F-15 avionics.

Dave

[dangus]

Just a wild guess... how did this unit "remember" settings? Is there a back-up battery that could have died?

[KISS]

dangus:

I got the good parts of the schematic scanned, so if you want to take a stab at "how things work", let me know. I'll send it to you.

It kept values in CMOS parts such as FF's. If you pulled the plug, all settings were lost. I hated that. No battery. You could not have the 4bx turn off power with convienience outlet.

The "ON" button had to be pushed twice. 1st time "mute". 2nd time "ON". Separate "OFF" button.

I riggged a "Fancy timer" and an opto-FET (to pulse the power off button of the 4bx) as the "SYSTEM" was turned off. Similarly when the 4bx was powered up an opto coupler in the 4bx would turn on the "SYSTEM" via the "Fancy timer", so I had on/off control via the remote of the 4bx as well as volume and 4bx levels.

The "Fancy timer" triac controlled the entire system with 3 modes of operation: 1) ON, 2) 10 min-2 hr timer and 3) OFF up to 10 minutes after the music stopped playing.

SYSTEM = Tuner, amp, signal processers, pre-amp etc,

[drmetric]

Greetings
I am in need of schematic drawings for my DBX 4BX.
Please let me know if these are available as I have been unable to find them anywhere. Thank you

[KISS]

Doc a.k.a. Johnny

Send me your email address.