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Delco Radio CDM Troubleshooting and Component Identification

bellarmine

Jun 28, 2022
6
Joined
Jun 28, 2022
Messages
6
Wow, those are quite different voltages! I did first check the voltages quickly in the truck with the control head plugged in, then since there seemed no difference I checked them in detail on my workbench. I'll double check tomorrow plugged into the control head again, and let you know if they're different.

To confirm, with the pins I assume you are starting at the Left side 12V pin and working over to the Right, alternating top and bottom rows back and forth? (from Left: top 1, bot 2, top 3, bot 4, top 5 etc.......). Like this?
Mine Off :: 1-12.6, 2- 0, 3- 0.2, 4- 0.6, 5-3.2, 6- 0, 7- 0, 8-4.9, 9-11.9, 10-5.0, 11- 0
Yours Off: 1-12.5, 2-12.5, 3-12.5, 4-12.5, 5-7.3, 6-12.5, 7-12.5, 8-7.4, 9- 0.6, 10-7.4, 11-12.5
Yours On: 1-12.4, 2- 4.3, 3- 2.3, 4- 7.4, 5-7.2, 6-12.4, 7-12.4, 8-7.3, 9- 0.6, 10-7.3, 11- 7.3

You have a good point about boosting the truck / voltage transients. I probably boosted the truck at some point after finding my scrapyard CDM, I was always changing batteries, connecting other booster batteries, boosting other vehicles, so lots of nice sparks there. My Dad was saying the same thing as you, probably not designed well enough for voltage spikes. You would think the GM engineers would keep that in mind, but I guess this was 'new' in the 80s-90s, so not done well enough.........

Yes, my regulator also says 44222 on it. You've managed to find an equivalent of some sort? I can't find any specs on these. That would be great if you tried one of your similar regulators to see what happens.

Another idea. Do you have a pinout? My Dad was saying if I could figure what voltages are needed, I could just supply 5V to the board and see if it functions, then just replace the regulator IC with separate regulator chips for the different voltages.

Thanks once again, this is getting interesting. Bellarmine
 

H2814D

Nov 4, 2017
110
Joined
Nov 4, 2017
Messages
110
Wow, those are quite different voltages! I did first check the voltages quickly in the truck with the control head plugged in, then since there seemed no difference I checked them in detail on my workbench. I'll double check tomorrow plugged into the control head again, and let you know if they're different.

To confirm, with the pins I assume you are starting at the Left side 12V pin and working over to the Right, alternating top and bottom rows back and forth? (from Left: top 1, bot 2, top 3, bot 4, top 5 etc.......). Like this?
Mine Off :: 1-12.6, 2- 0, 3- 0.2, 4- 0.6, 5-3.2, 6- 0, 7- 0, 8-4.9, 9-11.9, 10-5.0, 11- 0
Yours Off: 1-12.5, 2-12.5, 3-12.5, 4-12.5, 5-7.3, 6-12.5, 7-12.5, 8-7.4, 9- 0.6, 10-7.4, 11-12.5
Yours On: 1-12.4, 2- 4.3, 3- 2.3, 4- 7.4, 5-7.2, 6-12.4, 7-12.4, 8-7.3, 9- 0.6, 10-7.3, 11- 7.3

You have a good point about boosting the truck / voltage transients. I probably boosted the truck at some point after finding my scrapyard CDM, I was always changing batteries, connecting other booster batteries, boosting other vehicles, so lots of nice sparks there. My Dad was saying the same thing as you, probably not designed well enough for voltage spikes. You would think the GM engineers would keep that in mind, but I guess this was 'new' in the 80s-90s, so not done well enough.........

Yes, my regulator also says 44222 on it. You've managed to find an equivalent of some sort? I can't find any specs on these. That would be great if you tried one of your similar regulators to see what happens.

Another idea. Do you have a pinout? My Dad was saying if I could figure what voltages are needed, I could just supply 5V to the board and see if it functions, then just replace the regulator IC with separate regulator chips for the different voltages.

Thanks once again, this is getting interesting. Bellarmine
When checking the pins, with the code numbering facing me and the component upright, the far left pin is number one. The next one over is 2, until the last one on the far right is number 11. So yes, top to bottom alternating 1 thru 11.

I will try and breadboard the new components I have sourced. I found some L2750's in Germany and bought them. I have them here now. They also have another number on them that makes me think they are the right ones, L88HA, which I have seen somewhere else while researching these before, possibly on another CDM. Others that I sourced in China were L294, and L6203. I'm not sure about those at all. I bought more of the L2750's from China at the same time, because something tells me that is probably the right one. I'll get these on the breadboard, apply some voltage, and see what the pins show. The only way for me to check if they work in the CDM would be to possibly sacrifice a working CDM with one of the replacements I have and if they are wrong, I may damage a completely working CDM. That's why I haven't tried it yet.

I don't have a pin-out for the original component because the numbers don't come up. GM/Delco was famous for putting their own numbers on the chips, to throw us off, I'm sure. :-(

I'll let you know what happens after I test these. It may take me a day or two though.
 

bellarmine

Jun 28, 2022
6
Joined
Jun 28, 2022
Messages
6
Sounds good, whenever you get to it will be great, thank you. I double checked my voltage measurements again in the truck with the control head plugged in and turned on. Almost no change, all the 0's are still there, I just get 0.4v vs 0.2v / 4.8v vs 3.2v / and I think 5.4v vs 4.9v. Otherwise identical. Definitely dead chip.

I looked up your L2750 datasheet, yes it sure does seem like it should work. I like your reasoning, maybe between all those chips you'll find something, I mean Delco had to buy them from somewhere, they didn't make them themselves. Yes I love the way they re-number things, makes it real fun! I once had a piece of equipment where they potted the entire 8.5x11 board! What a mess.
https://www.digchip.com/datasheets/parts/datasheet/456/L2750.php

An idea, before you potentially 'blow-up' one of your good CDMs, why don't you try a chip on one of your non-working CDMs. That way you risk less, if it works great, and if it doesn't work you've lost nothing and can then consider trying a working CDM, having perhaps gained some information.

In the meantime I might consider taking the heatsink off my older unit and replacing those axial caps to save what's left of my power amp chips. Who knows, I might get 3 out of 4 (or better) (I'm an optimist...:eek:)

Did you hear about the BIG Internet and Cell outage we just had up here in Canada? Rogers Communications went down for 24 hours, no Internet, Cell phones, Gas pumps, Interac Debit, small run on the banks had to pay Cash for everything - mini-End of the World scenario for 24 hours, a little bit chilling....:eek:)

Do let me know how it goes when you have the chance, very much appreciate it! Best wishes and have a good Sunday!

Bellarmine
 

H2814D

Nov 4, 2017
110
Joined
Nov 4, 2017
Messages
110
Sounds good, whenever you get to it will be great, thank you. I double checked my voltage measurements again in the truck with the control head plugged in and turned on. Almost no change, all the 0's are still there, I just get 0.4v vs 0.2v / 4.8v vs 3.2v / and I think 5.4v vs 4.9v. Otherwise identical. Definitely dead chip.

I looked up your L2750 datasheet, yes it sure does seem like it should work. I like your reasoning, maybe between all those chips you'll find something, I mean Delco had to buy them from somewhere, they didn't make them themselves. Yes I love the way they re-number things, makes it real fun! I once had a piece of equipment where they potted the entire 8.5x11 board! What a mess.
https://www.digchip.com/datasheets/parts/datasheet/456/L2750.php

An idea, before you potentially 'blow-up' one of your good CDMs, why don't you try a chip on one of your non-working CDMs. That way you risk less, if it works great, and if it doesn't work you've lost nothing and can then consider trying a working CDM, having perhaps gained some information.

In the meantime I might consider taking the heatsink off my older unit and replacing those axial caps to save what's left of my power amp chips. Who knows, I might get 3 out of 4 (or better) (I'm an optimist...:eek:)

Did you hear about the BIG Internet and Cell outage we just had up here in Canada? Rogers Communications went down for 24 hours, no Internet, Cell phones, Gas pumps, Interac Debit, small run on the banks had to pay Cash for everything - mini-End of the World scenario for 24 hours, a little bit chilling....:eek:)

Do let me know how it goes when you have the chance, very much appreciate it! Best wishes and have a good Sunday!

Bellarmine
OK. So I put power to the L2750 out of a circuit. I'm sure it will not tell me much doing it this way, and I think the experts here have mentioned that before, in other posts, that it needs to be placed in a proper circuit for testing ( I know this anyway), but here is what I come up with:
Pin 1-Supply Voltage +12.5vdc, 2- 0, 3- 0, 4- 0, 5- 0, 6- Ground, 7- 0, 8- 0, 9- 11.5vdc, 10- 0, 11- 0.

With a complete working CDM and original component installed in it, but not hooked up to a Head Unit:
Pin 1- Supply Voltage +12.5vdc, 2- 0, 3- 0, 4- 0, 5- 4.9, 6- Ground, 7-0, 8- 5.0, 9- 12, 10- 5, 11- 0

This is my original component (M34AK) from the original CDM ^^^ I came to this forum for help with, and its readings. This one was done out of circuit. Oddly, quite a bit different:
Pin 1-Supply Voltage 12.0, 2- 8,75, 3- 8.69, 4- 3.98, 5- 7.9, 6- Ground, 7- 8.78, 9- 11.46, 10-8.33, 11- 8.75.

I installed the new L2750 into my original non-working CDM. I have the exact same problems as before. No display activity while using the volume controls, the clock or time set, and it didn't appear as if the frequency would change at all either to scan or pick up radio channels. So that didn't help. If you look at the datasheet you provided the link for, on page 4, it shows that component (L2750) in an audio circuit, even using two 470uF caps we have discussed earlier in the circuit, which we have in our CDM's. That gave me pretty high hopes when I saw that, but no luck after installing one in my original CDM.

Reference your half-working CDM. Note that the axial caps (I think they were 100uF) were not as important as the smaller 1uF green caps in between the amp chips. I read somewhere where those 1uF caps are what causes the amp chips to fail, and usually it's one or the other amp chip, but not both of them, which is probably why you are still getting some sound out of yours. If you can find them (the caps) it is just better to replace them all anyway. These units are 30+ years old.

I'm sure the "gurus" here are probably chuckling at our conversations, but I am an amateur at best with a few successes in several attempts with different electronics things, which is what drives me to continue, and they are pretty good and usually helpful at figuring things out for folks. And although I can glean some information off of a datasheet, my experiences with deciphering them is limited, so I can't really tell if the L2750 is a suitable replacement or not, without the datasheet for the original to compare it to.

I'm kind of stuck now, with the exception of pulling another working CDM power circuit component out and installing the L2750 in one. They are a pain to remove with all of those pins, but I've done it before. We will see.

Oh, nope. Didn't hear about your internet and phone issues down here. Let me know if you have any other ideas. Take care.
 
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