Jump to content

Extremely low output from my 6581's


Recommended Posts

Hi guys, new to the forum...I bought a sammichSID kit from the last batch this summer and after assembling it, still have not gotten it to work properly. I'm certain I've built the synth itself properly as it boots up, display is functional, I was able to load patches into it, etc... however my SIDs are just not functioning right. I have four 6581's lying around here and they all output an extremely quiet and unusable signal when I install them into the sammichSID.

I've had people who know a lot more than I do about electronics take a look at the board and they think the chips are just dead, which of course I'm willing to accept. But all four of them? At least one of them was working properly in the C64 it was pulled out of. And they're not all completely dead; they output *something* as quiet as it is. They respond to MIDI input properly, but only one voice seems to work. (I thought the sammichSID was laid out as 6 voices, one per oscillator?) I hear a loud popping sound as I switch patches.

I am using the recommended 12V Jameco 1A power supply. I have installed the proper capacitors for 6581's on the board. I've checked and re-checked the jumper configuration on the header pins. Pin 28 on each SID reads 12.45v, and for whatever it's worth, pin 27 reads slightly over 4v (don't know what to make of that). Both SIDs warm up noticeably after powerup but not hot to the touch.

Very excited about getting this synth working, so I am grateful for any support re: my problem. Even if the answer is just to get some new SIDs. Are mine finished or could something else be the cause of my woes?

Link to comment
Share on other sites

Well, for starters, you have the two SID audio buffer transistors (looks like they're called T1L and T1R) inserted in opposite ways, and the board around the top one looks discolored...

To make things more confusing, I believe it is the case that transistors made in Europe have their pins arranged opposite from those in America. Check the datasheet for the transistors you're using and then insert the transistor according to the schematics for the SID module (or sammichSID board). I'm not absolutely sure, but from the traces here it looks like that would be the top hole of the three for each, which means the little symbol on the board corresponds to a European transistor. Since the top one looks like it has the board discoloration around it, my guess is that one's backwards, and therefore that you're using European transistors (that are supposed to correspond to the symbol on the board).

Link to comment
Share on other sites

T1L is definitely mounted wrong. That would explain left channel not working.

There is no issue with European vs. American transistors... T1L and T1R are specified as BC547, and that's what I put in the kit. They should be mounted with the flat side matching the silkscreen.

As for the other channel not working, it could be due to bad solder joints. For example, the pins of C3L,C3R,C4L,C4R.

I also don't know what that pale looking stuff is on both sides of the board... is it flux residue? Did you attack it with a heat gun and burn the solder mask?

FWIW nearly all issues people have with sammichSID are due to poor soldering (esp. ground plane pads), or killing transistors by heating them too much.

Link to comment
Share on other sites

thanks for your replies guys. the transistors gave me a lot of grief.

re: T1L, the reason it looks like it's installed backwards is because it's not a BC547, it's a PN2222. different pinout. i had totally forgotten about this until you guys pointed it out. the reason it's not the original transistor that shipped with the kit, i believe i installed the original backwards and i damaged it while desoldering. a PN2222 was what was on hand for replacement.

the white stuff on the board is probably solder flux from desoldering/resoldering, etc...

for what it's worth i may have burned out T1 due to some bad jumper placement... i could smell it when i had the jumpers in the wrong place once. i'm not really sure because before it happened, the board wasn't working properly anyway, so i have no idea.

is it worthwhile to test these transistors with my meter? i've never done it before but anyone can lay out how to do it, i'll report back here with the results.

or should i just replace all the transistors on this board and see what happens?

Edited by zoinknoise
Link to comment
Share on other sites

The transistors cost around 10cents each, so I´d desolder them and ask questions later :D

Cut them above the frontside PCB with a wire cutter, then suck through each pin with a vacuum desoldering pump - heating from the backside with your iron while sucking from the frontside :-D.

Then, rework the solder points that look a bit messy, make sure your soldering iron has the right temperature and do quick soldering, it should not take more than 2 seconds per solder joint.

Being this fast also makes sure, that you don´t accidentally burn your new transistors. What really helps, is a temperature controlled quality iron with a new tip, and good (not lead-free) quality solder.

Also, you should get rid of that solder flux, your gfs or co-workers nailpaint remover will help here - there may be micro solder particles hidden below, creating unwanted shorts.

Many greets,


Edited by Hawkeye
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Create New...