Dean Markly CD-30 Tube Amp has me baffled...

[Morhawk]

I will try to make this quick but thorough. The amp powered up and hissed, but no output. Retubed amp (6L6, 12Ax7's). Amp will work with FX Loop patched (but the gain/drive selection still will not with this patched). Without the patch if I max out volume I hear the guitar faintly. I have read that could be bad jacks for the fx loop. I disconnected the small board with FX Loop (also contains Power Amp In + Preamp out jacks). This lead to faint guitar maxed volume. I "hardwired" the connections for the FX Loop jacks on the circuit board to the closed position so I could make sure it was not the contacts inside the jacks not connecting when there was no 1/4" placed in them and same problem.

Any hints would be great and WELL appreciated.. Thanks

[Enzo]

Let us be clear. You say with a cord plugged from FX send to FX return the amp works?? But the preamp doesn;t? I don;t quite understand.

[Morhawk]

Yes, when the FX loop is patched like that it works, although the gain and drive functions on the front have no effect on sound. I only get clean sound this way. Without the loop patched, only get a minute sound when cranked. I have three new 12AX7s in it, they should be good. (glowing, not microphonic).

[Morhawk]

There is a "Voicing" button on the front above the gain and drive pots. I assume this is clean/dirty. Unsure of channels, as I have never had it working. There is an LED below this knobs also. The switch is good and the LED is good (tested both) and pressing the button has no effect on the sound (with patch cable) and under both (patched and unpatched FX) the LED does not light up.

[Enzo]

Furst thing comes to my mind is perhaps the low voltage power supplies are missing. If the LED doesn't light, and the preamp controls are not right, look for the power supply for the low voltage circuits. 15VDC MAYBE?

[Morhawk]

Possibly, just has me baffled, I am not an expert by far. And I can not find the schematics for this old beast anywhere..lol When the loop is patched, all the other pots function (Treble, Midrange, volume).. I am trying to figure out where the signal goes that is different between the fx loop and when the fx loop is bypassed. Can't understand why that would make a difference.

[Enzo]

My mental image is focusing a little. First, the loop jacks. The return jack has a cutout contact, and when the loop is NOT in use, that contact carries the signal past those jacks. When you do use the loop, that contact is pushed open so the signal has to flow out through the loop and back. SO if the cutout contact on the return jack is dirty, oxidized, bent, whatever, the signal won't pass unless you plug a cable in.

I suspect the rest of it is a separate problem. It is starting to sound to me from your description that the amp is simply stuck in the clean channel. The overdrive controls have no effect because you can;t get to them. You can push the button, but without the voltage supply, the circuits can;t switch over. At least that is what my insides are telling me to look for.


Have you tried contacting either Dean MArkley or Kaman to ask if they have schematics?

[Morhawk]

Yeah, I suspected the jacks, I actually went on the board where the jacks connect and soldered a jumper on the connections that correlated to the contacts you speak of. It acts the same as no patch cable. Minimal output when cranked. I was thinking about contacting Dean Markley during the week about the schematics.

[Morhawk]

A better way to word this.. If I use a patch cable for the effects loop, I get the clean channel. If no patch cable, then i get no channels. Unless I crank it quite high, I get a crackly low output.

[Enzo]

As I suspected, you have a problem with your loop jacks, and when you bypass them it reveals that you ALSO have a p-roblem with one of your preamp channels.

[Morhawk]

I soldered the loop jacks with jumpers in case the contacts inside were shot, it was the same as no loop jacks. I am sure the jacks are good, I tested them to make sure the contacts were bypassing the jack when there was no plug in it, but I am thinking it may be something on the small board the jacks are contained. I believe this is going to be something out of my abilities to fix. I am not sure how to test the ic's and all that. All large capacitors, pots, and switches are good. I know how to test them..lol I was just hoping that there may be another common issue that would cause this issue.
I have read that these amps had a problem with the transformers, but it is getting power when it's looped.

I acctually got this amp out of the garbage on the curb, and spent $120 on tubes for it hoping. Maybe when I get some spare money I'll take it in to a pro.. :-(

[Chuck H]

Morhawk, I don't think you understand the switching jack circuit Enzo wrote about. To do a proper bypass you need to be sure you jumpered direct from the preamp out to the effects in, bypassing the jacks altogether. If, for example, you jumper the jacks from their hot lugs, this may not work depending on the switch type on the jack and that switches condition. You say the jacks are good, but how can you know that? Did you remove them from the circuit and test all contacts and switching function with and without a plug in the hole? Hmmmm?

Chuck

[Enzo]

Well, I am right up the road in Lansing, if you need someone to look at it.

COnsider a drive to Lansing some thursday evening - the day Elderly Instruments is open late until 9PM. Drop off the amp and visit that great old store across town.


Not that there are not plenty of competent people down where you are, I am sure there are. But if you need me, 517-882-2544. M-F AFTER 6:30PM.

[LaroldC]

Hey, try this page for schematics...

If you even still have this amp, that is! The string ended back in November!

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