Well... first off, I installed a light kit into the buttons a couple weeks ago. I used red LED's because I was using red buttons/lens but used the resistor values listed for the white LED's. I wasn't thinking and obviously this is wrong. BUT all worked fine. The LED's under the buttons were very dim compared to the knob LED's and yesterday I went in and changed the 1K array to a 100 Ohm array. This seeme like a good fix and all was fine. I thought the display seemed a bit dim though and there was a bright vertical line on the right side about 2 pixels wide but only where writing would be. Well, I got in the car and drove home and it was definitely dimmer. Getting in the car today, I couldn't read ANYTHING on the display. So this afternoon I went back to the 1K array... problem was not solved with the dim display. I tried with the array out as well and there was no noticeable difference in brightness

After much searching, I found the dimmer fix (didn't work) and things referring to the power capacitor. I did the power capacitor voltage check and I'm WAY low (23V)! I checked the fuse to the display and it was fine. I checked the power capacitor itself and it reads as 111nF and is listed as 100 nF in the posts. So I'm a bit at a loss as to where to go from here. I cheked various pins on the Max chip and got no more than 5V anywhere. What should I check from here? I think (and I stress think right now) I have the capability to repair what is wrong if someone can give me some direction on what components/pins should have what voltage on them. I was having trouble following the vias through the board to what is connected where

My player is an MK2a

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thinking and obviously this is wrong.

Red FILTERS red.

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I went in and changed the 1K array to a 100 Ohm array

Oh oh .... I can see this coming....

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I tried with the array out as well and there was no noticeable difference in brightness

Too late, you've already damaged it.

Not sure what you mean about the "power capacitor". There is a black thingy on the back of the display that is the power supply inductor (100 micro henries), and two large electrolytic capacitors (in series, voltage across them should be 57 - 64 V DC).

I think you have damaged the HT supply circuit to the VFD, which is why it's dim. You may be lucky and have avoided damage to the display itself, but I'm not holding my breath.

If you have checked the voltage on the TP1 point (top end of the two electros on the back of the board) and it's at 25V, then you have probably killed the power transistor TR4 (the BSP373). Either that or one of the two caps has perforated (C19, or C18). Measure the voltage across each of the caps first (DC) and report back what you've got.

I hate to say it, but I wish you would post for advice here FIRST before doing this sort of thing: I am not saying you are no good at this, but it might be worth checking on stuff like this before you try it. You might have seen my post about this elsewhere.....

I like to live on the edge

I will check those things and report the value tomorrow if I have time while at work to do it... The 24V was measured at the test point as specified in the FAQ. Thanks so much for your help. I had the 100 ohm array in there originally and it was all fine. I didn't have the knob LED board in at that time, though.

One of the capacitors, the one with the positive leda connecting to the test point reads 23.6V and the negtive lead reads 0V. Likewise the negative leg of the other cap measures 0V and the positive leg reads 11.1V

What else should I check or rather what does this mean?

There's a resistor around there that we've seen go bad in the past. I don't remember which one it is, but I think it's around 22 Ohms. It rests behind the VFD near the top.

Hope this helps,
Stu

I checked as many resistors as I could for both continuity and value... nothing showed up. I ordered a cross referenced part from Mouser for the BSP373 listed above...

Another oddity this morning which tells me it may not be the display itself. I had mentioned that it had a bright line to the right of the screen that was at or near the brightness level the whole display SHOULD be. Well, it was fairly cold her overnight (14F) and when I got in the car it was sunny so I saw no display... but then looked closer and there was no birght line on the right! The whole display was dim as it has been, but the line was gone! As the car warmed up more, the line returned. I thoguht that was a bit odd

OK... Now I'm wondering... I went through the other night and did searches on the Max770(I swear my display board said Max771 but the FAQ lists it as Max770 in the dim display section) chip and looked carefully at the reference designs. I see how the BSP373 is utilized in the circuitry now and how the feedback on the MAX 770 is what provides the gain. I was able to identify that the chip referenced in the DImmer issue is actually setting the resistance on the feedback loop to provide the "boost" (Or so my understanding is). Anyway, I was not able to find a problem when poking around on things.

So... I put the unit back in the car and was driving for quite a bit when suddenly the display gets VERY bright again... not as bright as normal, I guess, but normal is in my mind. At first I thought it was an illusion but then I realized that i could see it during the day again somewhat through the red lens. When I was able to check, the 25V that I was reading was now reading 46V! The line to the right is still there and evident, but not as noticeable with a brighter display. I can live with this but think it's probably caused somehow by the lower voltage as the brighter the display got, the dimmer the line was. I replaced the BSP373 with a ST cross referenced part and the voltage still is staying at 47.

I'm wondering, though. I noticed in a few other posts that Tony, for example, had mentioned he thought his display was dimmer since installing the lighted buttons but I don't know if a voltage was taken to see if the voltage was still in the recommended 55-63 range. I guess I'm trying to figure out if this is just a resultant issue from the lighted buttons or is there still another problem. I am going to look at the 100nF capacitor mentioned as failing a bit closer when i return to work and perhaps replace that.

Of course I should be happy with what I have now, but would like things to at least be correct. Also... does anyone have a source for the AD8400 dimmer chips? I'm only finding the SOIC versions now which it was clearly pointed out they were not able to find when in production. I'm guessing the phone industry no longer uses them and they became available.

Yeah, I'm curious what comes out of this, because I've wondered if my display is dimmer than it should be since I put in the button kit.

It might all be a moot point for me, eventually, as I've got a crack in my VFD and it's only a matter of time before it becomes fatal.

Tony, any chance you could measure your voltage at the test point mentioned in the FAQ?

Ours measures 60.7 volts with the light kit running. Makes no difference.

Stu

Thanks... I was just wondering... Now I'm leaning towards that cap or perhaps the AD8400. I'll check them more when I get back into work

Can anyone point me to the general location of theparts for the incoming power supply? I believe that now may be the issue. With the Empeg plugged into 12V power adapter, I only have 11V getting to the display. Is this normal? I wouldn't think there would be this sort of power drop when the chip is spec'd at 12V

Yes, this is about right. The input protection circuit includes at least one series diode, which will eat 0.6 of a volt or so. The empeg PSUs will actually work quite happily down to about 8.5v input voltage.

pca

Thanks for your quick response... I was thinking that this was the case but i could've sworn when I was originally looking at all of this that I had 12V at the fuse for the VFD board and now it's 11... but I guess my memory failed me...

Sorry, I have just noticed what I wrote here: Aaagh.

The display PSU inductor is 22 milli henries.

My apologies.

I have an idea: could you photograph and post your attachments of the rotary illumination board here?

I can when it all comes apart again.... but just so you know, I tried disconnecting that too and nothing changed... still 46V tops. Why I was leaning towards a power input to that section issue is that I brought my player in to add some things and when I plugged it in to the wall, sometimes the display was back being unreadable. Then I'd plug it in again and all is bright again. It is NOT a power supply issue because this has been confirmed with 2 different power supplies now - the original Empeg one and another switching 12V/2.5A supply.