Peavey DPM4 D/A converter

[Gtr_tech]

I was given 3 of these in various states of non-workingness. The best of the lot operates, but has *very* weak audio output until it warms for about 5 mins, then the output comes up along with a bunch of noise. Turn it off and back on and its back to little output for another 5 mins....leading me to believe its a digital problem. I don't have any service documentation on this unit, but I'd like to trace from the D/A convertor thru the analog stages. There is a D/A converter on the analog board, but its a single D/A. Since its stereo output I'd think there should be either 2 or a 2 channel D/A.

I've tried hitting everything with freeze spray, doesn't make the audio drop back out once it warms up. Only shutting it off resets the problem. Analog boards have been swapped with no difference, along with PSU boards. Cabling was been verified good end-to-end. I'm just going to give it away if I can get it running correctly. Anyone seen this problem?

[Enzo]

Don't count on another DA, simple enough to multiplex stereo out of one chip.

Call customer service down there, they'll send the schematics.

Is the battery good? Not worried about memory so much, but if there is any battery spooge on the board somewhere, it can raise havoc.


OK, I downloaded it, indeed stereo is multiplexed. My first thoughts are check the mute circuit, then maybe that 4053 or the op amp beside it.

DPM 3 or 4, same circuit

[bkahuna]

The batteries in these were famous (maybe infamous is better) for leaking and destroying the pcb. Make sure there is no corrosion around the battery. This can cause all sorts of problems. What you're describing sounds like it could be a mute circuit issue, as well.

As an aside: Peavey dealers used to have a form letter you could fill out for suggestions that went directly to Hartley Peavey. After seeing 3 or 4 of these pcbs destroyed by battery leakage, I sent a letter in, explaining what I'd seen and suggesting they use lithiums like the other manufacturers. I got a response from Hartley saying that " due to the high amount of memory used, lithiums didn't have the current capability to work properly, and btw, we're not aware of any damaged pcb issues." Total BS on both counts. If current was an issue, it was their choice of chips, rather than a deficiency in lithium batteries. All of their competitors successfully used lithiums, and I can't remember ever seeing a lithium leak...

[Gtr_tech]

2 out of the 3 had previously been in for service. I replaced the NiCd's with lithiums on those and disabled the charging circuit. No battery damage. And believe me, coming from the amusement machine industry I know all about that. Omega Race was a good example of a game that often got rendered useless due to the NiCd on the logic board that outgassed and ate up anything in its path. Unless its *very* minor, I won't touch battery damaged boards anymore.

[Enzo]

A couple times over the years I got a DPM with battery leakage, and I just sent the board to PV. The boards were ugly, but they came back clean as a whistle. At the factory they just depopulate the board, clean it and fill it back up. The result looked pristine, and worked fine, and cost darn little.


Oh lots of older Bally CPUs with corroded NiCads, and the whole bottom end of the board is corroded off. ANd the older original Gottlieb CPUs, the battery leaked and the whole row of Molex edgecons along the bottom edge to the driver card would fall apart.


In fairness to HArtley, those backup batteries will fail to function LONG before they spooge all over the board. Battery corrosion only occurs as a rule when the board has been sitting idle a long time. SO any keyboard in regular use will not get a corroded battery, a dead battery would have been replaced. Like a flashlight, a dead battery won't corrode a flashlight unless it sits in there for ages. If the battery dies while you are looking for the cat, the flashlight won't corrode before you get back to the kitchen. SO while there are tons of corroded flashlights, flashlights don;t have a corrosion problem, only neglected flashlights do.


ANyway, would love to hear what you find ultimately.

[Gtr_tech]

Do you really think they went through all that trouble to pull everything off the board to clean it and then re stuff it? I doubt that myself. It would be cheaper to just swap the pcb for a new one (or at least a used working one in good shape). The gas that comes from the NiCd batteries, if it doesn't eat off traces/pads/through plate vias completely, gets into the copper plating and makes it not want to take solder. Ever try to remove components from a battery damaged board? Its not easy since that gas altered the solder as well. Soldering back to the original pads usually is sketchy at best. If it takes solder after a scraping, great. If not, I'd relocate components to a place on the track that wasn't affected by the gas. Its nasty shit. Last time I attempted that was on a Korg Poly 61M. Got halfway through it and gave up. It was too far gone...

Its just not worth the time to piss with that kind of thing anymore. Yank (*RIP*) the battery off, toss the board in the parts board pile.

As far as the DPM here, I'll post back when I get a chance to get back into it. Since powering off and right back on brings the problem back after its already warmed, I'm thinking it could be the digital "go" line for the mute circuit. But we'll see.....

[Enzo]

If the copper had been corroded away, then no, I don;t expect they would try to solder to it. But if the corrosion had merely attacked the close pitch LSI legs in the area, and I didn;t fel like changing out a bunch of that crap, then yes, I expect they did exactly that. I believe I got back my same board in each case. I did read the repair bills. Doesn't seem likely to me they'd make up a component level story to cover a board swap. The choices are not just limited to A- 100% OK, and B- totally screwed. Boards can be in any condition in between those extremes. How many spare populated boards might they still have after 15 years?