DB54 - 2254 style compressor {update 22.10.19}

[MoJo]

Hi Everyone,

I have finished building the kit and am now testing and calibrating, and have run into an issue that maybe you all can help with.

First some background:

I have 33.8VAC at the power supply PCB input and 25.3 VDC at the output.

Following his instructions (which I have included a picture of):

1) No short between 24V and 0V pins.

2) No smoke after applying VDC.

3) BA185 pin f: 25.3VDC pin s: 25.3VDC
BA191 pin f: 25.3VDC pin n: 25.3VDC
BS283 pin m: 25.3VDC pin m: 25.3VDC

4) BA185 pin f: 22.3VDC pin s: 20.3VDC
BA191 pin f: 22.3VDC pin n: 22.3VDC
BS283 pin m: 22.3VDC pin m: 20.3VDC

5) Bias Calibration of TR3 on BA283 Card: I cannot get a reading of 2.3VDC on R7 no matter how I turn the RV1 trim resistor. I can only get a range of 8.5VDC to 9.4VDC.

Any ideas?

 

[JMan]

I am not the right person to help troubleshoot this, but I have a couple questions that might get the gears turning since no one else has responded yet.

1. Does your PSU use an adjustable linear regulator like an LM317? I don't think the slightly high voltage output would account for your trouble on the BA283 board, but it can't hurt to adjust it down to an nice tidy +24.

2. Have you double checked that you have the correct value trimpot for RV1? Maybe a greater resistance is needed to drop that voltage. Not saying that's the case, just wondering out loud.

3. The instructions don't specify which side of R7 you're supposed to be measuring. Did you measure each leg?

Sorry I can't be of more assistance...

 

[MoJo]

I am not the right person to help troubleshoot this, but I have a couple questions that might get the gears turning since no one else has responded yet.

1. Does your PSU use an adjustable linear regulator like an LM317? I don't think the slightly high voltage output would account for your trouble on the BA283 board, but it can't hurt to adjust it down to an nice tidy +24.

2. Have you double checked that you have the correct value trimpot for RV1? Maybe a greater resistance is needed to drop that voltage. Not saying that's the case, just wondering out loud.

3. The instructions don't specify which side of R7 you're supposed to be measuring. Did you measure each leg?

Sorry I can't be of more assistance...

Shoot Jman, you're a big help; please don't be sorry.

1) I set the PSU to exactly +24VDC

2) RV1 is a 5K Trimmer resistor and that is what the spec calls for.

3) One side of R7 shows 0.0066VDC, the other side shows 7.92VDC. I am using a Fluke 189 DMM with new batteries.

I double checked for any solder flows on BA283, but did not find any. I am going to send these readings to the kit designer and see what he says.

Thanks so much JMan; everything you can think of helps to eliminate another variable.

 

[MoJo]

Shoot Jman, you're a big help; please don't be sorry.

1) I set the PSU to exactly +24VDC

2) RV1 is a 5K Trimmer resistor and that is what the spec calls for.

3) One side of R7 shows 0.0066VDC, the other side shows 7.92VDC. I am using a Fluke 189 DMM with new batteries.

I double checked for any solder flows on BA283, but did not find any. I am going to send these readings to the kit designer and see what he says.

Thanks so much JMan; everything you can think of helps to eliminate another variable.

Jman, think it would hurt to put a bigger trimmer resistor in there? Like 50K?

 

[JMan]

You could certainly try. Maybe try a 20k and see if that has an impact.

Does this project come with a schematic? That would help. I suppose we could just grab the schematic for the original Neve BA283 board, that must be floating around here somewhere.

 

[MoJo]

You could certainly try. Maybe try a 20k and see if that has an impact.

Does this project come with a schematic? That would help. I suppose we could just grab the schematic for the original Neve BA283 board, that must be floating around here somewhere.

Hi JMan,

I ordered a 20K.

I found this schematic on the web and some supporting documentation.

 

[MoJo]

Here is a picture of my BA283 board to see if anyone can spot an obvious error.

 

[Undos]

Hi, without much analysis, two points to check. Have you measured the same voltage at the card pins with and without the cards connected ? see point 3 in the instructions. what type of transistors do you use ? In my unit I use NPN BC184c and are mounted the other way around. Emitter should go to the tag on the board from my expierence. Best

 

[Rob Flinn]

Here is a picture of my BA283 board to see if anyone can spot an obvious error.

View attachment 146009

The transistors look potentially the wrong way round. I don't know what transistors you are using but if they are BC184c then they are definitely the wrong way round.

 

[JMan]

Reversed transistors would be my guess as well

 

[MoJo]

I am using BC184C transistors. Thank you so much Undos, Rob Flinn and JMan. I questioned the orientation when I began to install them, and went with a picture of someone's build that I now realize did not use BC184c transistors. I am so thankful for your comments!

 

[MoJo]

So is the little tab on the PCB transistor symbol always the emitter side?

 

[JMan]

The tab in the footprint is there to help you orient your transistors assuming that you are using the metal can type. Since you're using transistors in the TO-92 package, I think your best bet is to check their pinout on the data sheet, then determine their orientation on the board using the schematic. Are all the transistors BC184C, or are there multiple types? If it's just BC184C, then once you work out the orientation of one, you'll be able to place the rest easily just by using the tab marking on the silkscreen.

 

[MoJo]

Most of the transistors are BC184 type, but there are a few others. I guess it's time I learn how to read a schematic! Thanks JMan.

 

[JMan]

It's a good opportunity to practice that skill, and because the BA283 board is single-sided, it will be extremely easy to follow the connections and understand how they match up to the schematic.

Honestly, this is giving me a little itch to dig out my set of boards and build this!

 

[Undos]

my answer contains errors and was too imprecise. sorry about that. follow JMan's instructions. Check the datasheet / pinout of the transistor and then compare it with the schematic/boards. don't forget to check the other 2 boards/cards as well. good luck

 

[MoJo]

Thanks Undos, I will check the other two boards.

And thank you JMan, I will do as you suggest.

I'm just so happy to find such helpful advice from you all.

 

[JMan]

I went ahead and dug out my boards this evening and started populating them with the components I have on hand. I had nearly all the right resistor values, the switches and relays, some caps, even the meter.

I do, however, now recall why I tabled this build in the first place - there are few things in DIY electronics that I enjoy less than tediously trying to work out appropriate substitutes for long-obsolete transistors. There's always one or two threads on the forum about what substitutions will work, but those threads are invariably already fifteen to twenty years old themselves and are often unhelpful (the comedy of looking up a suggested replacement only to find that it is now obsolete too). I found some BC441s for sale from an online retailer, so I'll give that a try. I also found some BC214LCs. Does anyone know if those are a useable substitute for the BC214KCs? Looking at a cross-reference sheet, I don't see any difference in specs. I'd have to check their data sheets to see if the pinout is the same or not, but that's easy enough to deal with.